www.zemarc.com hydraulics pneumatics controled motions bottom

Hydraulic engineering is a sub-discipline of civil engineering concerned with the flow and conveyance of fluids, principally water. This area of engineering is intimately related to the design of bridges, dams, channels, canals, levees, elevators, and to both sanitary and environmental engineering.

Contents [hide]
1 Applications
2 History
3 See also
4 External links

[edit] Applications
Common topics of design for hydraulic engineers includes hydraulic structures, including dams and levees, water distribution networks, water collection networks, storm water management, sediment transport, and various other topics related to transportation engineering and geotechnical engineering. Equations developed from the principles of fluid dynamics are frequently utilized by traffic engineers.

Related branches include hydrology, hydraulic modeling, flood mapping, catchment flood management plans, shoreline management plans, estuarine strategies, coastal protection, and flood alleviation.

[edit] History
Hydraulic engineering had already been highly developed under the Roman Empire where it was especially applied to the construction and maintenance of aqueducts. They used hydraulic mining methods to prospect and extract alluvial gold deposits in a technique known as hushing, and applied the methods to other ores such as those of tin and lead.

The recent best-selling historical novel Pompeii has such a Roman hydraulic engineer ("aquarius" in Latin) as its main protagonist.

In ancient China, hydraulic engineering was highly developed, and engineers constructed massive canals with levees and dams to channel the flow of water for irrigation. Sunshu Ao is considered the first hydraulic engineer. Another important Hydraulic Engineer in China, Ximen Bao was credited of starting the practice of large scale canal irrigation during the Warring States Period (481 BC-221 BC), even today hydraulic engineers remain a respectable position in China. Before becoming President, Hu Jintao was a hydraulic engineer and holds an engineering degree from Qinghua University

Modern hydraulic engineering involves the use of computer software such as HEC-RAS to perform the calculations to accurately predict flow characteristics.

[edit] See also
Hydraulic mining
International Association of Hydraulic Engineering and Research
Sunshu Ao
Ximen Bao
Henri Pitot
Effect of Hurricane Katrina on New Orleans
Significant modern floods
HEC-RAS
For the mechanical technology, see hydraulic machinery and hydraulic cylinder
Hydraulics is a topic of science and engineering dealing with the mechanical properties of liquids. Hydraulics is part of the more general discipline of fluid power. Fluid mechanics provides the theoretical foundation for hydraulics, which focuses on the engineering uses of fluid properties. Hydraulic topics range through most science and engineering disciplines, and cover concepts such as pipe flow, dam design, fluidics and fluid control circuitry, pumps, turbines, hydropower, computational fluid dynamics, flow measurement, river channel behavior and erosion. However if used incorrectly, hydraulic instruments can result in weird occurrences because of the nature of high pressure fluids.

The word "hydraulics" originates from the Greek word ?d?a?????? (hydraulikos) which in turn originates from ?d?a???? (hydraulos) meaning water organ which in turn comes from ?d?? (hydor, Greek for water) and a???? (aulos, meaning pipe).

Contents [hide]
1 Ancient and medieval era
1.1 Hellenistic world
1.2 China
1.3 Sri Lanka
1.4 Roman Innovations
1.5 Muslim innovations
2 Modern era
2.1 Benedetto Castelli
2.2 Blaise Pascal
2.3 Jean Louis Marie Poiseuille
3 See also
4 References
5 External links

[edit] Ancient and medieval era

[edit] Hellenistic world
The earliest masters of hydraulics in the Greek-Hellenized West were Ctesibius (flourished c. 270 BC) and Hero of Alexandria (c. 10–80 AD). Hero describes a number of working machines using hydraulic power, such as the force pump, which is known from many Roman sites as having been used for raising water and in fire engines, for example.

[edit] China
In ancient China there was Sunshu Ao (6th century BC), Ximen Bao (5th century BC), Du Shi (circa 31 AD), Zhang Heng (78 - 139 AD), and Ma Jun (200 - 265 AD), while medieval China had Su Song (1020 - 1101 AD) and Shen Kuo (1031 - 1095). Du Shi employed a waterwheel to power the bellows of a blast furnace producing cast iron. Zhang Heng was the first to employ hydraulics to provide motive power in rotating an armillary sphere for astronomical observation.

[edit] Sri Lanka

Moat and gardens at Sigirya.In ancient Sri Lanka, the Sinhalese used hydraulics in many applications, in the ancient kingdoms of Anuradhapura and Polonnaruwa. The discovery of the principle of the valve tower, or valve pit, for regulating the escape of water is credited to Sinhalese ingenuity more than 2,000 years ago. By the first century A.D, several large-scale irrigation works had been completed. Macro- and micro-hydraulics to provide for domestic horticultural and agricultural needs, surface drainage and erosion control, ornamental and recreational water courses and retaining structures and also cooling systems were in place in Sigiriya, Sri Lanka. The citadel on the massive rock at the site includes cisterns for collecting water. Special note is made on the pioneer Hydraulic Engineer, King Pandukabhaya (474-407BC) and Parakramabahu the Great on the hydraulic history of Sri Lanka.

[edit] Roman Innovations

Aqueduct of SegoviaThe Romans developed many different hydraulic applications, including public water supplies, innumerable aqueducts, power using watermills and hydraulic mining. They were among the first to make use of the siphon to carry water across valleys, and used hushing on a large scale to prospect for and then extract metal ores. They used lead widely in plumbing systems for domestic and public supply, such as feeding thermae.

While there is great public awareness of their highly visible aqueducts, less is known about their use of hydropower, although extant remains suggest that it was much more widespread than appreciated. The use of hydraulic mining methods is at its most spectacular in the gold-fields of northern Spain, which was conquered by Augustus in 25 BC. The alluvial gold-mine of Las Medulas for example must be one of the largest of their mines and even today rivals modern mines in sheer size. It was worked by at least 7 long aqueducts, and the water streams were used to erode the soft deposits, and then wash the tailings for the valuable gold content.

[edit] Muslim innovations
See also: Inventions in the Islamic world and Muslim Agricultural Revolution

The double-action reciprocating suction piston pump with a valve and crankshaft-connecting rod mechanism, from a manuscript of Al-Jazari in 1206.In the medieval Islamic world, the advances in in fluid mechanics by Muslim physicists such as Abu Rayhan al-Biruni (973-1048)[1] and Al-Khazini (who invented the hydrostatic balance in 1121),[2] led to innovations in hydraulics by Arabic engineers and inventors. The Arab Empire had advanced domestic water systems such as water cleaning systems and advanced water transportation systems resulting in better agriculture, something that helped in issues related to Islamic hygienical jurisprudence.[3]

Muslim engineers made a number of innovative uses of watermills between the 8th and 13th centuries, including: the bridge mill, a unique type of mill that was built as part of the superstructure of a bridge;[4] geared gristmill[5] with trip hammers;[6] hydropowered forge and finery forge;[7] milling dam, used to provide additional power for milling;[8] paper mill;[9] shipmill, powered by water wheels mounted on the sides of large ships moored in midstream;[6] spiral scoop-wheel, a device which raises large quantities of water to ground level with a high degree of efficiency;[10] sugar refinery;[11] the situation of watermills in the underground irrigation tunnels of a qanat and on the main canals of valley-floor irrigation systems;[7] and the water turbine.[6] The first factory milling installations were also built by Muslim engineers throughout every city and urban community in the Islamic world. For example, the factory milling complex in 10th century Baghdad could produce 10 tonnes of flour every day.[12]

In the 9th century, the Banu Musa brothers introduced the use of differential pressures in their hydraulic devices.[13] They also invented "the earliest known mechanical musical instrument", in this case a hydropowered organ which played interchangeable cylinders automatically. According to Charles B. Fowler, this "cylinder with raised pins on the surface remained the basic device to produce and reproduce music mechanically until the second half of the nineteenth century."[14] They also invented an automatic water-powered flute player which appears to have been the first programmable machine.[15] Al-Jazari (1136-1206) created the first recorded designs of programmable humanoid robots, which were driven by hydraulics and were part of a boat with four automatic musicians that floated on a lake to entertain guests at royal drinking parties.[16] According to Charles B. Fowler, the automata were a "robot band" which performed "more than fifty facial and body actions during each musical selection."[17] He also invented a hand washing automaton incorporating a flush mechanism now used in modern flush toilets. It features a female humanoid automaton standing by a basin filled with water. When the user pulls the lever, the water drains and the female automaton refills the basin.[18] His "peacock fountain" was a more sophisticated hand washing device featuring humanoid automata as servants which offer soap and towels, dirven by advanced hydraulic-powered mechanisms.[19]

The mechanical flywheel, used to smooth out the delivery of power from a driving device to a driven machine, was invented by Ibn Bassal (fl. 1038-1075) of Islamic Spain for use in the chain pump (saqiya) and noria.[20] Al-Jazari invented a variety of machines for raising water in 1206,[21] as well as water mills and water wheels with cams on their axle used to operate automata in the late 12th century.[22] His invention of the crankshaft and connecting rod mechanism, which is central to modern machinery such as the internal combustion engine,[23] was first employed in his water-raising machines,[24] which included crank-driven and hydropowered saqiya chain pumps, and the first double-action suction piston pump with reciprocating motion.[25] The concept of minimizing intermittency is also first implied in one of al-Jazari's saqiya chain pumps.[26]

The monumental water clocks constructed by medieval Muslim engineers employed complex gear trains, arrays of automata, and weight-drives, while the escapement mechanism was present in the hydraulic controls they used to make heavy floats descend at a slow and steady rate.[27] The on/off switch, an important feedback control principle, was invented by Muslim engineers between the 9th and 12th centuries, and it was employed in a variety of water-powered automata and water clocks.[28] In 1206, Al-Jazari invented monumental water-powered astronomical clocks such as the "castle clock", a hydraulics-powered programmable analog computer, which could re-program the length of day and night every day,[29] display moving models of the Sun, Moon, and stars, and had a pointer which travelled across the top of a gateway and caused automatic doors to open every hour.[6] His hydraulics-powered elephant clock was the first to feature an automaton, flow regulator, and closed-loop system.[30] The float regulator was later employed in domestic water systems during the Industrial Revolution.[31]

[edit] Modern era

[edit] Benedetto Castelli
In 1619 Benedetto Castelli (1576 - 1578–1643), a student of Galileo Galilei, published the book Della Misura dell'Acque Correnti or "On the Measurement of Running Waters", one of the foundations of modern hydrodynamics. He served as a chief consultant to the Pope on hydraulic projects, i.e., management of rivers in the Papal States, beginning in 1626.[32]

[edit] Blaise Pascal
Blaise Pascal (1623–1662-1672) study of fluid hydrodynamics and hydrostatics centered on the principles of hydraulic fluids. His inventions include the hydraulic press, which multiplied a smaller force acting on a larger area into the application of a larger force totaled over a smaller area, transmitted through the same pressure (or same change of pressure) at both locations. Pascal's law or principle states that for an incompressible fluid at rest, the difference in pressure is proportional to the difference in height and this difference remains the same whether or not the overall pressure of the fluid is changed by applying an external force. This implies that by increasing the pressure at any point in a confined fluid, there is an equal increase at every other point in the container, i.e., any change in pressure applied at any point of the fluid is transmitted undiminished throughout the fluids.

[edit] Jean Louis Marie Poiseuille
A French physician, Poiseuille researched the flow of blood through the body and discovered an important law governing the rate of flow with the diameter of the tube in which flow occurred.

[edit] See also
Affinity laws
Hydraulic engineering
Hydraulic mining
Pneumatics
International Association of Hydraulic Engineering and Research

[hide]v • d • eHydraulics

Concepts Hydraulics · Hydraulic fluid · Fluid power · Hydraulic engineering

Technologies Machinery · Accumulator · Brake · Circuit · Cylinder · Drive system · Manifold · Motor · Power network · Press · Pump · Ram · Rescue tools

[edit] References
^ Mariam Rozhanskaya and I. S. Levinova (1996), "Statics", p. 642, in (Morelon & Rashed 1996, pp. 614-642):
"Using a whole body of mathematical methods (not only those inherited from the antique theory of ratios and infinitesimal techniques, but also the methods of the contemporary algebra and fine calculation techniques), Arabic scientists raised statics to a new, higher level. The classical results of Archimedes in the theory of the centre of gravity were generalized and applied to three-dimensional bodies, the theory of ponderable lever was founded and the 'science of gravity' was created and later further developed in medieval Europe. The phenomena of statics were studied by using the dynamic apporach so that two trends - statics and dynamics - turned out to be inter-related withina single science, mechanics. The combination of the dynamic apporach with Archimedean hydrostatics gave birth to a direction in science which may be called medieval hydrodynamics. [...] Numerous fine experimental methods were developed for determining the specific weight, which were based, in particular, on the theory of balances and weighing. The classical works of al-Biruni and al-Khazini can by right be considered as the beginning of the application of experimental methods in medieval science."

^ Robert E. Hall (1973). "Al-Khazini", Dictionary of Scientific Biography, Vol. VII, p. 346.
^ Islam: Empire of Faith, Part One, after the 50th minute.
^ Adam Lucas (2006), Wind, Water, Work: Ancient and Medieval Milling Technology, p. 62. BRILL, ISBN 9004146490.
^ Donald Routledge Hill (1996), "Engineering", p. 781, in (Rashed & Morelon 1996, pp. 751-95)
^ a b c d Donald Routledge Hill, "Mechanical Engineering in the Medieval Near East", Scientific American, May 1991, p. 64-69. (cf. Donald Routledge Hill, Mechanical Engineering)
^ a b Adam Lucas (2006), Wind, Water, Work: Ancient and Medieval Milling Technology, p. 65. BRILL, ISBN 9004146490.
^ Donald Routledge Hill (1996), "Engineering", p. 759, in (Rashed & Morelon 1996, pp. 751-95)
^ The Beginning of the Paper Industry, Foundation for Science Technology and Civilisation.
^ Donald Routledge Hill (1996), "Engineering", p. 774, in (Rashed & Morelon 1996, pp. 751-95)
^ Adam Robert Lucas (2005), "Industrial Milling in the Ancient and Medieval Worlds: A Survey of the Evidence for an Industrial Revolution in Medieval Europe", Technology and Culture 46 (1): 1-30 [10]
^ Donald Routledge Hill (1996), "Engineering", p. 783, in (Rashed & Morelon 1996, pp. 751-95)
^ Ancient Discoveries, Episode 12: Machines of the East, History Channel, http://www.youtube.com/watch?v=n6gdknoXww8, retrieved on 2008-09-06
^ Fowler, Charles B. (October 1967), "The Museum of Music: A History of Mechanical Instruments", Music Educators Journal 54 (2): 45-49
^ Teun Koetsier (2001). "On the prehistory of programmable machines: musical automata, looms, calculators", Mechanism and Machine theory 36, p. 590-591.
^ A 13th Century Programmable Robot. University of Sheffield.
^ Fowler, Charles B. (October 1967), "The Museum of Music: A History of Mechanical Instruments", Music Educators Journal 54 (2): 45-49
^ Rosheim, Mark E. (1994), Robot Evolution: The Development of Anthrobotics, Wiley-IEEE, pp. 9-10, ISBN 0471026220
^ Rosheim, Mark E. (1994), Robot Evolution: The Development of Anthrobotics, Wiley-IEEE, p. 9, ISBN 0471026220
^ Ahmad Y Hassan, Flywheel Effect for a Saqiya, History of Science and Technology in Islam.
^ Al-Jazari, The Book of Knowledge of Ingenious Mechanical Devices: Kitáb fí ma'rifat al-hiyal al-handasiyya, translated by P. Hill (1973). Springer.
^ Donald Routledge Hill (1996), A History of Engineering in Classical and Medieval Times, Routledge, p.224.
^ Donald Routledge Hill (1998). Studies in Medieval Islamic Technology II, p. 231-232.
^ Ahmad Y Hassan. The Crank-Connecting Rod System in a Continuously Rotating Machine, History of Science and Technology in Islam.
^ Ahmad Y Hassan, The Origin of the Suction Pump - Al-Jazari 1206 A.D., History of Science and Technology in Islam
^ Donald Routledge Hill, "Engineering", p. 776, in Roshdi Rashed, ed., Encyclopedia of the History of Arabic Science, Vol. 2, pp. 751-795, Routledge, London and New York
^ Donald Routledge Hill (1996), "Engineering", p. 794, in (Rashed & Morelon 1996, p. 751-95)
^ F. L. Lewis (1992), Applied Optimal Control and Estimation, Englewood Cliffs, Prentice-Hall, New Jersey.
^ Ancient Discoveries, Episode 11: Ancient Robots, History Channel, http://www.youtube.com/watch?v=rxjbaQl0ad8, retrieved on 2008-09-06
^ The Machines of Al-Jazari and Taqi Al-Din, Foundation for Science Technology and Civilization.
^ Ahmad Y Hassan, Transfer Of Islamic Technology To The West, Part II: Transmission Of Islamic Engineering, History of Science and Technology in Islam.
^ Benedetto Castelli (1576-1578-1643), The Galileo Project
This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (October 2007)

[edit] External links
International Association of Hydraulic Engineering and Research (IAHR)
National Fluid Power Association (NFPA)
Pascal's Principle and Hydraulics
The principle of hydraulics
IAHR media library Web resource of photos, animation & video
Wikibooks' [[wikibooks:|]] has more about this subject:
School science/Hydraulics demonstrationhello what up?

Retrieved from "http://en.wikipedia.org/wiki/Hydraulics"
Categories: Fluid mechanics | Hydraulics | Hydraulic engineering | Mechanical engineering | Environmental engineering | Greek loanwords
Hidden categories: Articles containing non-English language text | Articles needing additional references from October 2007From Wikipedia, the free encyclopedia
Jump to: navigation, search
Fluid power is the technology of exploiting the properties of fluids to generate, control, and transmit power as a result of the pressurization of fluids.

As the term fluid refers either to gases or to liquids, fluid power is also subdivided into the categories of hydraulics and pneumatics. The differences being that with hydraulics the medium used is a liquid (ie mineral oil or water) and for pneumatics it is a gas (ie air or another inert gas).

Contents [hide]
1 Practical use
1.1 Transport energy
2 Application
3 See also
4 References
5 External links

[edit] Practical use

[edit] Transport energy
A fluid power system starts with a pump driven by a prime mover (electric motor or IC engine) that converts mechanical energy in to fluid energy. This fluid flow is used to actuate a device specifically designed to operate from the flow provided. In general, these actuators fall into the following categories:

Cylinder (hydraulic or pneumatic): Provides force in a linear fashion
Motor (hydraulic or pneumatic): Provides continuous rotational motion
Rotary actuator: Provides rotational motion of less than 360 degrees.

[edit] Application
Hydraulics and pneumatics are similar in many ways, but there are clear reasons for using one over the other.

Cost: Pneumatics are considerably cheaper to build and operate. For one, air is used as the compressed medium, so no reservoir is needed to store fluid, nor is there any need to provide means to drain or recover fluid. With increasing working pressures, pneumatics require larger parts than hydraulics.
Precision: Unlike liquids, gases change volume significantly when pressurized making it difficult to achieve precision.
Safety: Gases tend to want to expand at high velocities when compressed, thus pneumatics are typically limited in utilities with a working pressure up to around 100 psi (7 bar).

[edit] See also
London Hydraulic Power Company
Pneumatics
Pneumatic circuit
Pneumatic actuator

[edit] References
Esposito, Anthony, Fluid Power with Applications, ISBN 0-13-010225-3
Hydraulic Power System Analysis, A. Akers, M. Gassman, & R. Smith, Taylor & Francis, New York, 2006, ISBN: 0-8247-9956-9

[edit] External links
Information about Fluid Power is also available on the National Fluid Power Association web-site nfpa.com
Using Equivalent Lengths of Valves and Fittings

This fluid dynamics-related article is a stub. You can help Wikipedia by expanding it.

Retrieved from "http://en.wikipedia.org/wiki/Fluid_power"
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This page was last modified on 9 January 2009, at 17:53. All text is available under the terms of the GNU Free Documentation License. (See Copyrights for details.)
Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a U.S. registered 501(c)(3) tax-deductible nonprofit charity.
Privacy policy About Wikipedia DisclaimersFrom Wikipedia, the free encyclopedia
Jump to: navigation, search
Fluid power is the technology of exploiting the properties of fluids to generate, control, and transmit power as a result of the pressurization of fluids.

Contents [hide]
1 Practical use
1.1 Transport energy
2 Application
3 See also
4 References
5 External links

[edit] Practical use

[edit] Application
Hydraulics and pneumatics are similar in many ways, but there are clear reasons for using one over the other.

[edit] See also
London Hydraulic Power Company
Pneumatics
Pneumatic circuit
Pneumatic actuator

[edit] External links
Information about Fluid Power is also available on the National Fluid Power Association web-site nfpa.com
Using Equivalent Lengths of Valves and Fittings

This fluid dynamics-related article is a stub. You can help Wikipedia by expanding it.

This page was last modified on 9 January 2009, at 17:53. All text is available under the terms of the GNU Free Documentation License. (See Copyrights for details.)
Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a U.S. registered 501(c)(3) tax-deductible nonprofit charity.
Privacy policy About Wikipedia Disclaimers From Wikipedia, the free encyclopedia
Jump to: navigation, search
Fluid power is the technology of exploiting the properties of fluids to generate, control, and transmit power as a result of the pressurization of fluids.

Contents [hide]
1 Practical use
1.1 Transport energy
2 Application
3 See also
4 References
5 External links

[edit] Practical use

[edit] Application
Hydraulics and pneumatics are similar in many ways, but there are clear reasons for using one over the other.

[edit] See also
London Hydraulic Power Company
Pneumatics
Pneumatic circuit
Pneumatic actuator

[edit] External links
Information about Fluid Power is also available on the National Fluid Power Association web-site nfpa.com
Using Equivalent Lengths of Valves and Fittings

This fluid dynamics-related article is a stub. You can help Wikipedia by expanding it.

This page was last modified on 9 January 2009, at 17:53. All text is available under the terms of the GNU Free Documentation License. (See Copyrights for details.)
Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a U.S. registered 501(c)(3) tax-deductible nonprofit charity.
Privacy policy About Wikipedia Disclaimers From Wikipedia, the free encyclopedia
Jump to: navigation, search
Fluid power is the technology of exploiting the properties of fluids to generate, control, and transmit power as a result of the pressurization of fluids.

Contents [hide]
1 Practical use
1.1 Transport energy
2 Application
3 See also
4 References
5 External links

[edit] Practical use

[edit] Application
Hydraulics and pneumatics are similar in many ways, but there are clear reasons for using one over the other.

[edit] See also
London Hydraulic Power Company
Pneumatics
Pneumatic circuit
Pneumatic actuator

[edit] External links
Information about Fluid Power is also available on the National Fluid Power Association web-site nfpa.com
Using Equivalent Lengths of Valves and Fittings

This fluid dynamics-related article is a stub. You can help Wikipedia by expanding it.

This page was last modified on 9 January 2009, at 17:53. All text is available under the terms of the GNU Free Documentation License. (See Copyrights for details.)
Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a U.S. registered 501(c)(3) tax-deductible nonprofit charity.
Privacy policy About Wikipedia Disclaimers From Wikipedia, the free encyclopedia
Jump to: navigation, search
Fluid power is the technology of exploiting the properties of fluids to generate, control, and transmit power as a result of the pressurization of fluids.

Contents [hide]
1 Practical use
1.1 Transport energy
2 Application
3 See also
4 References
5 External links

[edit] Practical use

[edit] Application
Hydraulics and pneumatics are similar in many ways, but there are clear reasons for using one over the other.

[edit] See also
London Hydraulic Power Company
Pneumatics
Pneumatic circuit
Pneumatic actuator

[edit] External links
Information about Fluid Power is also available on the National Fluid Power Association web-site nfpa.com
Using Equivalent Lengths of Valves and Fittings

This fluid dynamics-related article is a stub. You can help Wikipedia by expanding it.

This page was last modified on 9 January 2009, at 17:53. All text is available under the terms of the GNU Free Documentation License. (See Copyrights for details.)
Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a U.S. registered 501(c)(3) tax-deductible nonprofit charity.
Privacy policy About Wikipedia Disclaimers
Pneumatics
From Wikipedia, the free encyclopedia
Jump to: navigation, search
"Pneumatic" redirects here. For the highest order of humans in Gnosticism, see Pneumatic (Gnosticism).
Contents [hide]
1 Examples of pneumatic systems
2 Gases used in pneumatic systems
3 Comparison to hydraulics
3.1 Advantages of pneumatics
3.2 Advantages of hydraulics
4 Pneumatic Logic
5 See also

Pneumatics is the use of pressurized gas to affect mechanical motion.

Pneumatic power is used in industry, where factory machines are commonly plumbed for compressed air; other compressed inert gases can also be used. Pneumatics also has applications in dentistry, construction, mining, and other areas.

[edit] Examples of pneumatic systems
Pneumatic tools:
Pneumatic drill (jackhammer) used by road workers
Pneumatic nailgun
Pneumatic switches
Pneumatic actuator
Air compressors
Vacuum pump
Barostat systems used in Neurogastroenterology and for researching electricity
Cable jetting, a way to install cables in ducts
Pneumatic mail systems
Compressed-air engine and compressed-air vehicles
Air brakes on buses and trucks
Air brakes, on trains
Air engines for pneumatically powered vehicles
Lego pneumatics can be used to build pneumatic models
Pneumatic Launchers, a type of spud gun
Pneumatic air guns
Holman Projector, a pneumatic anti-aircraft weapon

[edit] Gases used in pneumatic systems
Pneumatic systems in fixed installations such as factories use compressed air because a sustainable supply can be made by compressing atmospheric air. The air usually has moisture removed and a small quantity of oil added at the compressor, to avoid corrosion of mechanical components and to lubricate them.

Factory-plumbed, pneumatic-power users need not worry about poisonous leakages as the gas is commonly just air. Smaller or stand-alone systems can use other compressed gases which are an asphyxiation hazard, such as nitrogen - often referred to as OFN (oxygen-free nitrogen), when supplied in cylinders.

Any compressed gas other than air is an asphyxiation hazard - including nitrogen, which makes up approximately 80% of air. Compressed oxygen (approx. 20% of air) would not asphyxiate, but it would be an extreme fire hazard, so is never used in pneumatically powered devices.

Portable pneumatic tools and small vehicles such as Robot Wars machines and other hobbyist applications are often powered by compressed carbon dioxide because containers designed to hold it such as soda stream canisters and fire extinguishers are readily available, and the phase change between liquid and gas makes it possible to obtain a larger volume of compressed gas from a lighter container than compressed air would allow. Carbon dioxide is both an asphyxiant and poisonous, and can also be a freezing hazard when vented.

[edit] Comparison to hydraulics
Both pneumatics and hydraulics are applications of fluid power. Pneumatics uses an easily compressible gas such as air or a suitable pure gas, while hydraulics uses relatively incompressible liquid media such as oil. Most industrial pneumatic applications use pressures of about 80 to 100 pounds per square inch (psi) (500 to 700 kilopascals). Hydraulics applications commonly use from 1,000 to 5,000 psi (7 to 35 MPa), but specialized applications may exceed 10,000 psi (70 MPa).

[edit] Advantages of pneumatics
Cleanliness

Simplicity of Design And Control
Machines are easily designed using standard cylinders & other components. Control is as easy as it is simple ON - OFF type control.
Reliability
Pneumatic systems tend to have long operating lives and require very little maintenance.
Because gas is compressible, the equipment is less likely to be damaged by shock. The gas in pneumatics absorbs excessive force, whereas the fluid of hydraulics directly transfers force.
Storage
Compressed Gas can be stored, allowing the use of machines when electrical power is lost.
Safety
Very small fire hazards (compared to hydraulic oil).
Machines can be designed to be overload safe.

[edit] Advantages of hydraulics
Fluid does not absorb any of the supplied energy.
Capable of moving much higher loads and providing much higher forces due to the incompressibility.
The hydraulic working fluid is basically incompressible, leading to a minimum of spring action. When hydraulic fluid flow is stopped, the slightest motion of the load releases the pressure on the load; there is no need to "bleed off" pressurised air to release the pressure on the load.

[edit] Pneumatic Logic
Main article: Fluidics
Pneumatic logic systems are often used to control industrial processes, consisting of primary logic units such as:

And Units
Or Units
'Relay or Booster' Units
Latching Units
'Timer' Units
Pneumatic logic is a reliable and functional control method for industrial processes. In recent years, these systems have largely been replaced by electrical control systems, due to the smaller size and lower cost of electrical components. Pneumatic devices are still used in processes where compressed air is the only energy source available or upgrade cost, safety, and other considerations outweigh the advantage of modern digital control.

[edit] See also
Fluidics
Hydraulics
Ozone cracking
Polymer degradation
Pneudraulics
Look up pneumatics in
Wiktionary, the free dictionary.
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This article is about the construction tool. For other uses, see Jackhammer (disambiguation).

A portable jackhammer being used to break up the road surface during roadworks. A pneumatic hose can be seen leading to the compressor on the back of the truck. The operator is using his body weight to increase the effectiveness of the device.
An excavator-mounted hydraulic jackhammer being used to break up the road surface during preparatory works for a new sewage line.A pneumatic drill or jackhammer is a portable percussive drill powered by compressed air (though the same type of equipment mounted to construction machinery can also be hydraulically powered). It is used to drill rock and break up pavement, among other applications. It works similar to a hammer and chisel, by jabbing with its bit, not rotating it. (A drill driven by compressed air, which rotates its cutting bit is called an air-drill or familiarly, a windy-drill or rotary hammer.) The word jackhammer is used in North American English and in Australia, and pneumatic drill is used colloquially elsewhere in the English speaking world, although (road) breaker is used in the trade.[1]

Contents [hide]
1 Overview
2 Air supply
3 Hydraulic operation
4 Electro-mechanical operation
5 Health
6 Bits
7 References
8 External links

[edit] Overview

Drilling a blast hole with a jackhammer, Douglas Dam on the French Broad River, Tennessee Valley Authority 1942.The portable pneumatic jackhammer is impractical for use on walls and steep slopes, as it relies on the inertia of the mass of its body to drive the bit into the work, and manipulating that mass when not supported by the work is difficult. Also, gravity is required to bring the mass back into contact with the work after each blow. Though it is unhealthy practice, the operator may lean on the tool to assist but is not really capable of overcoming the forces involved when not assisted by gravity. A technique developed by experienced laborers is the use of two man teams to overcome this obstacle of gravity. One laborer operates the hammer and the second assists by holding the hammer either on his shoulders or cradled in his arms. Both use their combined weight to push the bit into the workface. This method is commonly referred to as horizontal jackhammering. Another method is overhead jackhammering, requiring strength conditioning and endurance to hold a smaller jackhammer, called a rivet buster, over one's head.

Its pneumatic hose connections are designed so that any hose will connect with any other hose without attention to male and female hose-ends. see Gender of connectors and fasteners.

[edit] Air supply

Compressor for running a pneumatic drill / jackhammer.The air supply for a jackhammer usually comes from a portable compressor driven by a diesel engine. Reciprocating compressors were formerly used. The unit comprised a reciprocating compressor driven, through a centrifugal clutch, by a diesel engine. The engine's governor provided only two speeds:

idling, when the clutch was disengaged
maximum, when the clutch was engaged and the compressor was running
Modern versions use rotary compressors and have more sophisticated variable governors. The unit is usually mounted on a trailer and sometimes includes an electrical generator to supply lights or electric power tools. Makes of portable compressor sold in the UK include Atlas Copco, CompAir and Ingersoll Rand.

[edit] Hydraulic operation
A hydraulic jackhammer, much larger than portable ones, may be fitted to mechanical excavators or backhoes and is widely used for roadwork, quarrying and general demolition or construction groundwork. In mining, it is possible to use this against a vertical wall as the machine can be braced against the opposite wall of the gallery or some comparable device. Pneumatic tools are likely to be used in underground coal mines due to safety concerns.

Hydraulic breakers usually use a hydraulic motor driving a sealed pneumatic hammer system, as a hydraulic hammer would develop a low strike speed and transfer unacceptable shock loads to the pump system.

[edit] Electro-mechanical operation

Makita single phase demolition breaker.While the term "jackhammer" is occasionally used to mean "pneumatic drill", the electromechanical tool that performs the same function is normally the one called a "jackhammer" in Britain. This tool is useful where the work is light and inaccessible to compressor.

The Makita breaker pictured uses standard 25mm (1") points and chisels identical to the ones used in medium sized pneumatic tools. It uses 1300 Watts of power and weighs about 19 kg (about 42 pounds) with a point installed.

This type and size of machine is commonly rented by amateurs for renovation jobs.

[edit] Health

Pneumatic drill / jackhammer, with black silencer attachedThe sound of the hammer blows, combined with the explosive air exhaust, makes pneumatic jackhammers dangerously loud, emitting 100 decibels at two meters. Sound-blocking earmuffs must be worn by the operator to prevent a form of hearing damage of which tinnitus is the main symptom. Most pneumatic jackhammers now have a silencer around the barrel of the tool, which is the black item in the image.

Prolonged exposure to the pronounced vibration set up by the tool can lead to blood-circulation failures in the fingers, a condition known as white finger. Applying athletic tape is not effective in preventing white finger but seems to help alleviate some of its discomfort. Pneumatic drill usage can also lead to a predisposition for development of carpal tunnel syndrome.

[edit] Bits
Spade - provides flat finish for concrete or edging in asphalt or dirt
Flat tip - allows direction control or finer edge finish
Point - general breaking
Stake driver - drives concrete form stakes
Scrabbler - finishes surface smooth or for cleaning prior to bonding

[edit] References
^ How It Works - Horobin, Wendy; Marshall Cavendish Corporation, Third Edition, Page 1195
Pneumatic actuator
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A pneumatic actuator converts energy (in the form of compressed air, typically) into motion. The motion can be rotary or linear, depending on the type of actuator. Some types of pneumatic actuators include:

Tie rod cylinders
Rotary actuators
Grippers
Rodless actuators with magnetic linkage or rotary cyclinders
Rodless actuators with mechanical linkage
Pneumatic artificial muscles
Speciality actuators that combine rotary and linear motion--frequently used for clamping operations
Vacuum generators
A Pneumatic actuator mainly consists of a piston, a cylinder, and valves or ports. The piston is covered by a diaphragm, or seal, which keeps the air in the upper portion of the cylinder, allowing air pressure to force the diaphragm downard, moving the piston underneath, which in turn moves the valve stem, which is linked to the internal parts of the actuator. Pneumatic actuators may only have one spot for a signal input, top or bottom, depending on action required. Valves require little pressure to operate and usually double or triple the input force. The larger the size of the piston, the larger the output pressure can be. Having a larger piston can also be good if air supply is low, allowing the same forces with less input. These pressures are large enough to crush object in the pipe. On 100 kPa input, you could lift a small car (upwards 1,000 lbs) easily, and this is only a basic, small pneumatic valve. However, the resulting forces required of the stem would be too great and cause the valve stem to fail.

This pressure is transferred to the valve stem, which is hooked up to either the valve plug (see plug valve), butterfly valve etc. Larger forces are required in high pressure or high flow pipelines to allow the valve to overcome these forces, and allow it to move the valves moving parts to control the material flowing inside.

Valves input pressure is the "control signal." This can come from a variety of measuring devices, and each different pressure is a different set point for a valve. A typical standard signal is 20-100 kPa. For example, a valve could be controlling the pressure in a vessel which has a constant out-flow, and a varied in-flow (varied by the actuator and valve). A pressure transmitter will monitor the pressure in the vessel and transmit a signal from 20-100 kPa. 20 kPa means there is no pressure, 100 kPa means there is full range pressure (can be varied by the transmiters calibration points). As the pressure rises in the vessel, the output of the transmitter rises, this increase in pressure is sent to the valve, which causes the valve to stroke downard, and start closing the valve, decreasing flow into the vessel, reducing the pressure in the vessel as excess pressure is evacuated through the out flow. This is called a direct acting process.
Gas compressor
From Wikipedia, the free encyclopedia
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A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.

Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas. Liquids are relatively incompressible, so the main action of a pump is to transport liquids.

Contents [hide]
1 Types of compressors
1.1 Centrifugal compressors
1.2 Diagonal or mixed-flow compressors
1.3 Axial-flow compressors
1.4 Reciprocating compressors
1.5 Rotary screw compressors
1.6 Rotary vane compressors
1.7 Scroll compressors
1.8 Diaphragm compressors
2 Temperature
3 Staged compression
4 Prime movers
5 Applications
6 See also
7 References

[edit] Types of compressors
The main types of gas compressors are illustrated and discussed below:

[edit] Centrifugal compressors
Main article: Centrifugal compressor

Figure 1: A single stage centrifugal compressorCentrifugal compressors use a rotating disk or impeller in a shaped housing to force the gas to the rim of the impeller, increasing the velocity of the gas. A diffuser (divergent duct) section converts the velocity energy to pressure energy. They are primarily used for continuous, stationary service in industries such as oil refineries, chemical and petrochemical plants and natural gas processing plants.[1][2][3] Their application can be from 100 hp (75 kW) to thousands of horsepower. With multiple staging, they can achieve extremely high output pressures greater than 10,000 psi (69 MPa).

Many large snow-making operations (like ski resorts) use this type of compressor. They are also used in internal combustion engines as superchargers and turbochargers. Centrifugal compressors are used in small gas turbine engines or as the final compression stage of medium sized gas turbines.

[edit] Diagonal or mixed-flow compressors
Main article: Diagonal or mixed-flow compressor
Diagonal or mixed-flow compressors are similar to centrifugal compressors, but have a radial and axial velocity component at the exit from the rotor. The diffuser is often used to turn diagonal flow to the axial direction. The diagonal compressor has a lower diameter diffuser than the equivalent centrifugal compressor.

[edit] Axial-flow compressors
Main article: Axial-flow compressor

An animation of an axial compressor.Axial-flow compressors are dynamic rotating compressors that use arrays of fan-like aerofoils to progressively compress the working fluid. They are used where there is a requirement for a high flow rate or a compact design.

The arrays of aerofoils are set in rows, usually as pairs: one rotating and one stationary. The rotating aerofoils, also known as blades or rotors, accelerate the fluid. The stationary aerofoils, also known as a stators or vanes, turn and decelerate the fluid; preparing and redirecting the flow for the rotor blades of the next stage.[1] Axial compressors are almost always multi-staged, with the cross-sectional area of the gas passage diminishing along the compressor to maintain an optimum axial Mach number. Beyond about 5 stages or a 4:1 design pressure ratio, variable geometry is normally used to improve operation.

Axial compressors can have high efficiencies; around 90% polytropic at their design conditions. However, they are relatively expensive, requiring a large number of components, tight tolerances and high quality materials. Axial-flow compressors can be found in medium to large gas turbine engines, in natural gas pumping stations, and within certain chemical plants.

[edit] Reciprocating compressors

A motor-driven six-cylinder reciprocating compressor that can operate with two, four or six cylinders.Main article: Reciprocating compressor
Reciprocating compressors use pistons driven by a crankshaft. They can be either stationary or portable, can be single or multi-staged, and can be driven by electric motors or internal combustion engines.[1][4] [5] Small reciprocating compressors from 5 to 30 horsepower (hp) are commonly seen in automotive applications and are typically for intermittent duty. Larger reciprocating compressors well over 1,000 hp (750 kW) are still commonly found in large industrial and petroleum applications. Discharge pressures can range from low pressure to very high pressure (>6000 psi or 41.4 MPa). In certain applications, such as air compression, multi-stage double-acting compressors are said to be the most efficient compressors available, and are typically larger, noisier, and more costly than comparable rotary units.[6]

[edit] Rotary screw compressors

Diagram of a rotary screw compressorMain article: Rotary screw compressor
Rotary screw compressors use two meshed rotating positive-displacement helical screws to force the gas into a smaller space.[1][7][8] These are usually used for continuous operation in commercial and industrial applications and may be either stationary or portable. Their application can be from 3 hp (2.24 kW) to over 500 hp (375 kW) and from low pressure to very high pressure (>1200 psi or 8.3 MPa).

[edit] Rotary vane compressors
See also: Rotary vane pump
Rotary vane compressors consist of a rotor with a number of blades inserted in radial slots in the rotor. The rotor is mounted offset in a larger housing which can be circular or a more complex shape. As the rotor turns, blades slide in and out of the slots keeping contact with the outer wall of the housing.[1] Thus, a series of decreasing volumes is created by the rotating blades. Rotary Vane compressors are, with piston compressors one of the oldest of compressor technologies.

With suitable port connections, the devices may be either a compressor or a vacuum pump. They can be either stationary or portable, can be single or multi-staged, and can be driven by electric motors or internal combustion engines. Dry vane machines are used at relatively low pressures (e.g., 2 bar) for bulk material movement whilst oil-injected machines have the necessary volumetric efficiency to achieve pressures up to about 13 bar in a single stage. A rotary vane compressor is well suited to electric motor drive and is significantly quieter in operation than the equivalent piston compressor.

[edit] Scroll compressors
Main article: Scroll compressor

Mechanism of a scroll pumpA scroll compressor, also known as scroll pump and scroll vacuum pump, uses two interleaved spiral-like vanes to pump or compress fluids such as liquids and gases. The vane geometry may be involute, archimedean spiral, or hybrid curves.[9][10][11] They operate more smoothly, quietly, and reliably than other types of compressors in the lower volume range

Often, one of the scrolls is fixed, while the other orbits eccentrically without rotating, thereby trapping and pumping or compressing pockets of fluid or gas between the scrolls.

[edit] Diaphragm compressors
Main article: Diaphragm compressor
A diaphragm compressor (also known as a membrane compressor) is a variant of the conventional reciprocating compressor. The compression of gas occurs by the movement of a flexible membrane, instead of an intake element. The back and forth movement of the membrane is driven by a rod and a crankshaft mechanism. Only the membrane and the compressor box come in touch with the gas being compressed.[1]

Diaphragm compressors are used for hydrogen and compressed natural gas (CNG) as well as in a number of other applications.

A three-stage diaphragm compressorThe photograph included in this section depicts a three-stage diaphragm compressor used to compress hydrogen gas to 6,000 psi (41 MPa) for use in a prototype compressed hydrogen and compressed natural gas (CNG) fueling station built in downtown Phoenix, Arizona by the Arizona Public Service company (an electric utilities company). Reciprocating compressors were used to compress the natural gas.

The prototype alternative fueling station was built in compliance with all of the prevailing safety, environmental and building codes in Phoenix to demonstrate that such fueling stations could be built in urban areas.

[edit] Temperature
Main article: Gas laws
Compression of a gas naturally increases its temperature.

In an attempt to model the compression of gas, there are two theoretical relationships between temperature and pressure in a volume of gas undergoing compression. Although neither of them model the real world exactly, each can be useful for analysis. A third method measures real-world results:

Isothermal - This model assumes that the compressed gas remains at a constant temperature throughout the compression or expansion process. In this cycle, internal energy is removed from the system as heat at the same rate that it is added by the mechanical work of compression. Isothermal compression or expansion more closely models real life when the compressor has a large heat exchanging surface, a small gas volume, or a long time scale (i.e., a small power level). Compressors that utilize inter-stage cooling between compression stages come closest to achieving perfect isothermal compression. However, with practical devices perfect isothermal compression is not attainable. For example, unless you have an infinite number of compression stages with corresponding intercoolers, you will never achieve perfect isothermal compression.
Adiabatic - This model assumes that no energy (heat) is transferred to or from the gas during the compression, and all supplied work is added to the internal energy of the gas, resulting in increases of temperature and pressure. Theoretical temperature rise is T2 = T1·Rc(k-1)/k, with T1 and T2 in degrees Rankine or kelvins, and k = ratio of specific heats (approximately 1.4 for air). R is the compression ratio; being the absolute outlet pressure divided by the absolute inlet pressure. The rise in air and temperature ratio means compression does not follow a simple pressure to volume ratio. This is less efficient, but quick. Adiabatic compression or expansion more closely model real life when a compressor has good insulation, a large gas volume, or a short time scale (i.e., a high power level). In practice there will always be a certain amount of heat flow out of the compressed gas. Thus, making a perfect adiabatic compressor would require perfect heat insulation of all parts of the machine. For example, even a bicycle tire pump's metal tube becomes hot as you compress the air to fill a tire.
Polytropic - This model takes into account both a rise in temperature in the gas as well as some loss of energy (heat) to the compressor's components. This assumes that heat may enter or leave the system, and that input shaft work can appear as both increased pressure (usually useful work) and increased temperature above adiabatic (usually losses due to cycle efficiency). Compression efficiency is then the ratio of temperature rise at theoretical 100 percent (adiabatic) vs. actual (polytropic).
In the case of the fire piston and the heat pump, people desire temperature change, and compressing gas is only a means to that end.

[edit] Staged compression
In the case of centrifugal compressors, commercial designs currently do not exceed a compression ratio of more than a 3.5 to 1 in any one stage. Since compression generates heat, the compressed gas is to be cooled between stages making the compression less adiabatic and more isothermal. The inter-stage coolers typically result in some partial condensation that is removed in vapor-liquid separators.

In the case of small reciprocating compressors, the compressor flywheel may drive a cooling fan that directs ambient air across the intercooler of a two or more stage compressor.

Because rotary screw compressors can make use of cooling lubricant to remove the heat of compression, they very often exceed a 9 to 1 compression ratio. For instance, in a typical diving compressor the air is compressed in three stages. If each stage has a compression ratio of 7 to 1, the compressor can output 343 times atmospheric pressure (7 x 7 x 7 = 343 atmospheres).

[edit] Prime movers
There are many options for the "prime mover" or motor which powers the compressor:

gas turbines power the axial and centrifugal flow compressors that are part of jet engines
steam turbines or water turbines are possible for large compressors
electric motors are cheap and quiet for static compressors. Small motors suitable for domestic electrical supplies use single phase alternating current. Larger motors can only be used where an industrial electrical three phase alternating current supply is available.
diesel engines or petrol engines are suitable for portable compressors and support compressors used as superchargers from their own crankshaft power. They use exhaust gas energy to power turbochargers

[edit] Applications
Gas compressors are used in various applications where either higher pressures or lower volumes of gas are needed:

in pipeline transport of purified natural gas to move the gas from the production site to the consumer.
in petroleum refineries, natural gas processing plants, petrochemical and chemical plants, and similar large industrial plants for compressing intermediate and end product gases.
in refrigeration and air conditioner equipment to move heat from one place to another in refrigerant cycles: see Vapor-compression refrigeration.
in gas turbine systems to compress the intake combustion air
in storing purified or manufactured gases in a small volume, high pressure cylinders for medical, welding and other uses.
in many various industrial, manufacturing and building processes to power all types of pneumatic tools.
as a medium for transferring energy, such as to power pneumatic equipment.
in pressurised aircraft to provide a breathable atmosphere of higher than ambient pressure.
in some types of jet engines (such as turbojets and turbofans) to provide the air required for combustion of the engine fuel. The power to drive the combustion air compressor comes from the jet's own turbines.
in SCUBA diving, hyperbaric oxygen therapy and other life support devices to store breathing gas in a small volume such as in diving cylinders.
in submarines, to store air for later use in displacing water from buoyancy chambers, for adjustment of depth.
in turbochargers and superchargers to increase the performance of internal combustion engines by increasing mass flow.
in rail and heavy road transport to provide compressed air for operation of rail vehicle brakes or road vehicle brakes and various other systems (doors, windscreen wipers, engine/gearbox control, etc).
in miscellaneous uses such as providing compressed air for filling pneumatic tires.

[edit] See also
Cabin pressurization
Centrifugal fan
Compressed air
Variable speed air compressor
Gas compression heat pump
Fire piston
Hydrogen compressor
Liquid ring compressor
Roots blower (a lobe-type compressor)
Pneumatic cylinder
Pneumatic tube
Pressurization
Vapor-compression refrigeration

[edit] References
^ a b c d e f Perry, R.H. and Green, D.W. (Editors) (2007). Perry's Chemical Engineers' Handbook (8th Edition ed.). McGraw Hill. ISBN 0-07-142294-3.
^ Dixon S.L. (1978). Fluid Mechanics, Thermodynamics of Turbomachinery (Third Edition ed.). Pergamon Press. ISBN 0-08-022722-8.
^ Aungier, Ronald H. (2000). Centrifugal Compressors A Strategy for Aerodynamic design and Analysis. ASME Press. ISBN 0-7918-0093-8.
^ Bloch, H.P. and Hoefner, J.J. (1996). Reciprocating Compressors, Operation and Maintenance. Gulf Professional Publishing. ISBN 0-88415-525-0.
^ Reciprocating Compressor Basics Adam Davis, Noria Corporation, Machinery Lubrication, July 2005
^ Introduction to Industrial Compressed Air Systems
^ Screw Compressor Describes how screw compressors work and include photographs.
^ Technical Centre Discusses oil-flooded screw compressors including a complete system flow diagram
^ Tischer, J., Utter, R: “Scroll Machine Using Discharge Pressure For Axial Sealing,” U.S. Patent 4522575, 1985.
^ Caillat, J., Weatherston, R., Bush, J: “Scroll-Type Machine With Axially Compliant Mounting,” U.S. Patent 4767293, 1988.

Types
Pumps can be broadly categorized according to three techniques:[1]

Positive displacement pumps use a mechanism to repeatedly expand a cavity, allow gases to flow in from the chamber, seal off the cavity, and exhaust it to the atmosphere.
Momentum transfer pumps, also called molecular pumps, use high speed jets of dense fluid or high speed rotating blades to knock gaseous molecules out of the chamber.
Entrapment pumps capture gases in a solid or absorbed state. This includes cryopumps, getters, and ion pumps.
Positive displacement pumps are the most effective for low vacuums. Momentum transfer pumps in conjunction with one or two positive displacement pumps are the most common configuration used to achieve high vacuums. In this configuration the positive displacement pump serves two purposes. First it obtains a rough vacuum in the vessel being evacuated before the momentum transfer pump can be used to obtain the high vacuum, as momentum transfer pumps cannot start pumping at atmospheric pressures. Second the positive displacement pump backs up the momentum transfer pump by evacuating to low vacuum the accumulation of displaced molecules in the high vacuum pump. Entrapment pumps can be added to reach ultrahigh vacuums, but they require periodic regeneration of the surfaces that trap air molecules or ions. Due to this requirement their available operational time can be unacceptably short in low and high vacuums, thus limiting their use to ultrahigh vacuums. Pumps also differ in details like manufacturing tolerances, sealing material, pressure, flow, admission or no admission of oil vapor, service intervals, reliability, tolerance to dust, tolerance to chemicals, tolerance to liquids and vibration.

[edit] Performance measures
Pumping speed refers to the volume flow rate of a pump at its inlet, often measured in volume per unit of time. Momentum transfer and entrapment pumps are more effective on some gases than others, so the pumping rate can be different for each of the gases being pumped, and the average volume flow rate of the pump will vary depending on the chemical composition of the gases remaining in the chamber.
Throughput refers to the pumping speed multiplied by the gas pressure at the inlet, and is measured in units of pressure·volume/unit time. At a constant temperature, throughput is proportional to the number of molecules being pumped per unit time, and therefore to the mass flow rate of the pump. When discussing a leak in the system or backstreaming through the pump, throughput refers to the volume leak rate multiplied by the pressure at the vacuum side of the leak, so the leak throughput can be compared to the pump throughput.
Positive displacement and momentum transfer pumps have a constant volume flow rate, (pumping speed,) but as the chamber's pressure drops, this volume contains less and less mass. So although the pumping speed remains constant, the throughput and mass flow rate drop exponentially. Meanwhile, the leakage, evaporation, sublimation and backstreaming rates continue to produce a constant throughput into the system.

[edit] Positive displacement

The manual water pump draws water up from a well by creating a vacuum that water rushes in to fill. In a sense, it acts to evacuate the well, although the high leakage rate of dirt prevents a high quality vacuum from being maintained for any length of time.
Mechanism of a scroll pumpFluids cannot be pulled, so it is technically impossible to create a vacuum by suction. Suction is the movement of fluids into a vacuum under the effect of a higher external pressure, but the vacuum has to be created first. The easiest way to create an artificial vacuum is to expand the volume of a container. For example, the diaphragm muscle expands the chest cavity, which causes the volume of the lungs to increase. This expansion reduces the pressure and creates a partial vacuum, which is soon filled by air pushed in by atmospheric pressure

To continue evacuating a chamber indefinitely without requiring infinite growth, a compartment of the vacuum can be repeatedly closed off, exhausted, and expanded again. This is the principle behind positive displacement pumps, like the manual water pump for example. Inside the pump, a mechanism expands a small sealed cavity to create a deep vacuum. Because of the pressure differential, some fluid from the chamber (or the well, in our example) is pushed into the pump's small cavity. The pump's cavity is then sealed from the chamber, opened to the atmosphere, and squeezed back to a minute size.

More sophisticated systems are used for most industrial applications, but the basic principle of cyclic volume removal is the same:

Rotary vane pump, the most common
Diaphragm pump, zero oil contamination
Liquid ring pump
Piston pump, cheapest
Scroll pump, highest speed dry pump
Screw pump (10 Pa)
Wankel pump
External vane pump
Roots blower, also called a booster pump, has highest pumping speeds but low compression ratio
Multistage Roots pump that combine several stages providing high pumping speed with better compression ratio
Toepler pump
The base pressure of a rubber- and plastic-sealed piston pump system is typically 1 to 50 kPa, while a scroll pump might reach 10 Pa (when new) and a rotary vane oil pump with a clean and empty metallic chamber can easily achieve 0.1 Pa.

A positive displacement vacuum pump moves the same volume of gas with each cycle, so its pumping speed is constant unless it is overcome by backstreaming.

[edit] Momentum transfer

A cutaway view of a turbomolecular high vacuum pumpIn a momentum transfer pump, gas molecules are accelerated from the vacuum side to the exhaust side (which is usually maintained at a reduced pressure by a positive displacement pump). Momentum transfer pumping is only possible below pressures of about 1 kPa. Matter flows differently at different pressures based on the laws of fluid dynamics. At atmospheric pressure and mild vacuums, molecules interact with each other and push on their neighboring molecules in what is known as viscous flow. When the distance between the molecules increases, the molecules interact with the walls of the chamber more often than the other molecules, and molecular pumping becomes more effective than positive displacement pumping. This regime is generally called high vacuum.

Molecular pumps sweep out a larger area than mechanical pumps, and do so more frequently, making them capable of much higher pumping speeds. They do this at the expense of the seal between the vacuum and their exhaust. Since there is no seal, a small pressure at the exhaust can easily cause backstreaming through the pump; this is called stall. In high vacuum, however, pressure gradients have little effect on fluid flows, and molecular pumps can attain their full potential.

The two main types of molecular pumps are the diffusion pump and the turbomolecular pump. Both types of pumps blow out gas molecules that diffuse into the pump by imparting momentum to the gas molecules. Diffusion pumps blow out gas molecules with jets of oil or mercury, while turbomolecular pumps use high speed fans to push the gas. Both of these pumps will stall and fail to pump if exhausted directly to atmospheric pressure, so they must be exhausted to a lower grade vacuum created by a mechanical pump.

As with positive displacement pumps, the base pressure will be reached when leakage, outgassing, and backstreaming equal the pump speed, but now minimizing leakage and outgassing to a level comparable to backstreaming becomes much more difficult.

Diffusion pump
Turbomolecular pump

[edit] Entrapment
Entrapment pumps may be cryopumps, which use cold temperatures to condense gases to a solid or adsorbed state, chemical pumps, which react with gases to produce a solid residue, or ionization pumps, which use strong electrical fields to ionize gases and propel the ions into a solid substrate. A cryomodule uses cryopumping.

Ion pump
Cryopump
Sorption pump
Non-evaporative getter

[edit] Other pump types
Venturi vacuum pump (aspirator) (10 to 30 kPa)
Steam ejector (vacuum depends on the number of stages, but can be very low)

[edit] Techniques
Vacuum pumps are combined with chambers and operational procedures into a wide variety of vacuum systems. Sometimes more than one pump will be used (in series or in parallel) in a single application. A partial vacuum, or rough vacuum, can be created using a positive displacement pump that transports a gas load from an inlet port to an outlet (exhaust) port. Because of their mechanical limitations, such pumps can only achieve a low vacuum. To achieve a higher vacuum, other techniques must then be used, typically in series (usually following an initial fast pump down with a positive displacement pump). Some examples might be use of an oil sealed rotary vane pump (the most common positive displacement pump) backing a diffusion pump, or a dry scroll pump backing a turbomolecular pump. There are other combinations depending on the level of vacuum being sought.

Achieving high vacuum is difficult because all of the materials exposed to the vacuum must be carefully evaluated for their outgassing and vapor pressure properties. For example, oils, and greases, and rubber, or plastic gaskets used as seals for the vacuum chamber must not boil off when exposed to the vacuum, or the gases they produce would prevent the creation of the desired degree of vacuum. Often, all of the surfaces exposed to the vacuum must be baked at high temperature to drive off adsorbed gases.

Outgassing can also be reduced simply by desiccation prior to vacuum pumping. High vacuum systems generally require metal chambers with metal O-ring seals such as Klein flanges or ISO flanges, rather than the rubber o-rings more common in low vacuum chamber seals. The system must be clean and free of organic matter to minimize outgassing. All materials, solid or liquid, have a small vapour pressure, and their outgassing becomes important when the vacuum pressure falls below this vapour pressure. As a result, many materials that work well in low vacuums, such as epoxy, will become a source of outgassing at higher vacuums. With these standard precautions, vacuums of 1 mPa are easily achieved with an assortment of molecular pumps. With careful design and operation, 1 µPa is possible.

Several types of pumps may be used in sequence or in parallel. In a typical pumpdown sequence, a positive displacement pump would be used to remove most of the gas from a chamber, starting from atmosphere (760 Torr, 101 kPa) to 25 Torr (3 kPa). Then a sorption pump would be used to bring the pressure down to 10-4 Torr (10 mPa). A cryopump or turbomolecular pump would be used to bring the pressure further down to 10-8 Torr (1 µPa). An additional ion pump can be started below 10-6 Torr to remove gases which are not adequately handled by a cryopump or turbo pump, such as helium or hydrogen.

Ultra high vacuum generally requires custom-built equipment, strict operational procedures, and a fair amount of trial-and-error. Ultra-high vacuum systems are usually made of stainless steel with metal-gasketed conflat flanges. The system is usually baked, preferably under vacuum, to temporarily raise the vapour pressure of all outgassing materials in the system and boil them off. If necessary, this outgassing of the system can also be performed at room temperature, but this takes much more time. Once the bulk of the outgassing materials are boiled off and evacuated, the system may be cooled to lower vapour pressures to minimize residual outgassing during actual operation. Some systems are cooled well below room temperature by liquid nitrogen to shut down residual outgassing and simultaneously cryopump the system.

In ultra-high vacuum systems, some very odd leakage paths and outgassing sources must be considered. The water absorption of aluminium and palladium becomes an unacceptable source of outgassing, and even the absorptivity of hard metals such as stainless steel or titanium must be considered. Some oils and greases will boil off in extreme vacuums. The porosity of the metallic chamber walls may have to be considered, and the grain direction of the metallic flanges should be parallel to the flange face.

The impact of molecular size must be considered. Smaller molecules can leak in more easily and are more easily absorbed by certain materials, and molecular pumps are less effective at pumping gases with lower molecular weights. A system may be able to evacuate nitrogen (the main component of air) to the desired vacuum, but the chamber could still be full of residual atmospheric hydrogen and helium. Vessels lined with a highly gas-permeable material such as palladium (which is a high-capacity hydrogen sponge) create special outgassing problems.
Pneumatic tubes (or capsule pipelines; Lamson tubes) are systems in which cylindrical containers are propelled through a network of tubes by compressed air or by vacuum. They are used for transporting physical objects, solid objects, compared to the more generic pipelines which transport gases or fluids.

Pneumatic tube networks gained great prominence in the late 19th and early 20th century for businesses or administrations that needed to transport small but urgent packages (such as mail or money) over relatively short distances (within a building, or, at most, within a city). Some of these systems grew to great complexity, but they were eventually superseded by more modern methods of communication and courier transport, and are now much rarer than before.

A small number of pneumatic transportation systems were also built for larger cargo, to compete with more standard train and subway systems. However, these never really took off as practical systems.

Contents [hide]
1 History
2 For postal service
2.1 Historical use
3 For transportation
4 Current usage
5 In fiction
6 See also
7 References
8 External links

[edit] History
Pneumatics can be traced back to Hero of Alexandria in the 1st century AD, though there was apparently no thought of using them to move objects through pipes.

Pneumatic capsule transportation was originally invented by Phineas Balk in 1806.[citation needed] Though a marvel of the time, and a successful sideshow, it was considered little more than a novelty until the invention of the capsule in 1836.[citation needed] The Victorians were the first to use capsule pipelines to transmit telegraph messages, or telegrams, to nearby buildings from telegraph stations.

While they are commonly used for small parcels and documents — now most often used at banks or supermarkets[1] — they were originally proposed in the early 1800s for transport of heavy freight. It was once envisioned that networks of these massive tubes might be used to transport people.

[edit] For postal service

Pneumatic tube letter from Berlin, Germany, 1902
Italian pneumatic post stamp, 1945Pneumatic post or pneumatic mail is a system to deliver letters through pressurized air tubes. It was invented by the Scottish engineer William Murdoch in the 1800s and was later developed by the London Pneumatic Dispatch Company. Pneumatic post systems were used in several large cities starting in the second half of the 19th century (including an 1866 London system powerful enough to transport humans)[2], but were largely abandoned during the 20th century.

It was also speculated that a system of tubes might deliver mail to every home in the US. A major network of tubes in Paris was in use until 1984, when it was finally abandoned in favor of computers and fax machines. In Prague, in the Czech Republic, a network of tubes extending approximately 60 kilometres in length still exists for delivering mail and parcels. Following the 2002 European floods and damage sustained, operation of the Prague system was mothballed indefinitely.

Typical current applications are in banks and hospitals. Many large retailers use pneumatic tubes to transport cheques or other documents from cashiers to the accounting office. One system lists a speed of 10 meters per second. [1]

Pneumatic post stations usually connected post offices, stock exchanges, banks and ministries. Italy was the only country to issue postage stamps (between 1913 and 1966) specifically for pneumatic post. Austria, France, and Germany issued postal stationery for pneumatic use.

[edit] Historical use
1853: linking the London Stock Exchange to the city's main telegraph station (a distance of 220 yards)
1865: in Berlin (until 1976), the Rohrpost, a system 400 kilometers in total length at its peak in 1940
1866: in Paris (until 1984, 467 kilometers in total length from 1934)
1875: in Vienna (until 1956)
1887: in Prague (until 2002 due to flooding), the Prague pneumatic post, [2]
1897: in New York City (until 1953)
other cities: Munich, Rio de Janeiro, Buenos Aires, Hamburg, Rome, Naples, Milan, Marseilles, Melbourne, Boston, Philadelphia, Chicago, St. Louis

[edit] For transportation
(Pneumatic Transportation here in general refers to the transporting of people inside pneumatic tubes.)

In 1812, George Medhurst first proposed, but never implemented, blowing passenger carriages through a tunnel.

Atmospheric railways, on which the tube was laid between the rails, with a piston running in it suspended from the train through a sealable slot in the top of the tube, were operated as follows:[3]

1844-54: Dublin and Kingstown Railway's Dalkey Atmospheric Railway between Kingstown (Dún Laoghaire) and Dalkey, Ireland (1.75 mi (3 km))
1846-47: London and Croydon Railway between Croydon and New Cross, London, England (7.5 mi (12 km))
1847-48: Isambard Kingdom Brunel's South Devon Railway between Exeter and Newton Abbot, England (20 mi (32 km))
1847-60: Paris–Saint-Germain railway between Bois de Vésinet and Saint-Germain-en-Laye, France (2 km (1 mi))
In 1861, the Pneumatic Despatch Company built a system large enough to move a person, although it was intended for parcels. The October 10, 1865 inauguration of the new Holborn Station was marked by having the Duke of Buckingham, the chairman, and some of the directors of the company blown through the tube to Euston (a five minute trip).

The 550-meter Crystal Palace pneumatic railway was exhibited at the Crystal Palace in 1864. This was a prototype for a proposed Whitehall Pneumatic Railway that would have run under the River Thames linking Waterloo and Charing Cross. Digging commenced in 1865 but was halted in 1868 due to financial problems.

Alfred Ely Beach's experimental pneumatic elevated subway on display in 1867In 1867 at the American Institute exhibition in New York, Alfred Ely Beach demonstrated a 32.6 m long, 1.8 m diameter pipe that was capable of moving 12 passengers plus a conductor. In 1869, the Beach Pneumatic Transit Company of New York constructed in secret a 95 m long, 2.7 m diameter pneumatic subway line under Broadway. The line only operated for a few months, closing after Beach was unsuccessful in getting permission to extend it.

In the 1960s, Lockheed and MIT with the United States Department of Commerce conducted feasibility studies on a vactrain system powered by ambient atmospheric pressure and "gravitational pendulum assist" to connect cities on the East Coast of the US. They calculated that the run between Philadelphia and New York City would average 174 meters per second, that is 626 km/h (388 mph).

When those plans were abandoned as too expensive, Lockheed engineer L.K. Edwards founded Tube Transit, Inc. to develop technology based on "gravity-vacuum transportation". In 1967 he proposed a Bay Area Gravity-Vacuum Transit for California that would run alongside the then-under construction BART system. It was never built.

[edit] Current usage
The technology is still used on a smaller scale. In North America, a large number of drive-up banks use pneumatic tubes to transport cash and documents between cars and tellers. Most hospitals have a computer-controlled pneumatic tube system to deliver drugs, documents and specimens to and from laboratories and nurses' stations. Many factories use them to deliver parts quickly across large campuses. Many larger stores use systems to securely transport excess cash from checkout stands to back offices, and to send change back to cashiers. NASA's original Mission Control Center in Houston, Texas had pneumatic tubes connecting controller consoles with staff support rooms. Denver International Airport is noteworthy for the large number of pneumatic tube systems, including a 25 cm diameter system for moving aircraft parts to remote concourses, a 10 cm system for United Airlines ticketing, and a robust system in the parking toll collection system with an outlet at every booth.

In Britain, the House of Commons telephone and computer exchange also has a pneumatic tube system in place.

[edit] In fiction

The pneumatic tube train from Albert Robida's The Twentieth Century.When pneumatic tubes first came into use in the 19th century, they symbolized technological progress and it was imagined that they would be common in the future. Jules Verne's Paris in the 20th Century (1863) includes suspended pneumatic tube trains that stretch across the oceans. Albert Robida's The Twentieth Century (1882) describes a 1950s Paris where tube trains have replaced railways, pneumatic mail is ubiquitous, and catering companies compete to deliver meals on tap to people's homes through pneumatic tubes. Edward Bellamy's Looking Backward (1888) envisions the world of 2000 as interlinked with tubes for delivering goods. Michel Verne's An Express of the Future (1888) questions the sensibility of a transatlantic pneumatic subway. In Michel & Jules Verne's The Day of an American Journalist in 2889 (1889) submarine tubes carry people faster than aero-trains and the Society for Supplying Food to the Home allows subscribers to receive meals pneumatically.

Later, because of their use by governments and large businesses, tubes began to symbolize bureaucracy. In George Orwell's Nineteen Eighty-Four, pneumatic tubes in the Ministry of Truth deliver newspapers to Winston's desk containing articles to be "rectified". (In the same year of writing as Orwell's book (1949) Robert Heinlein's novella Gulf offered a more neutral view of their use in general postal delivery.)

In 1985, the movie Brazil, which has similar themes to Nineteen Eighty-Four, also used tubes (as well as other anachronistic-seeming technologies) to evoke the stagnation of bureaucracy. At the start of each episode of the 1998 television series Fantasy Island, a darker version of the original, bookings for would-be visitors to the Island were sent to the devilish Mr. Roarke via a pneumatic tube from a dusty old travel agency, making the tube seem not so much bureaucratic as sinister.

The failure of pneumatic tubes to live up to their potential as envisioned in previous centuries has placed them in the company of flying cars and dirigibles as ripe for ironic retro-futurism. The 1960s cartoon series The Jetsons featured pneumatic tubes that people could step into and be sucked up and swiftly spit out at their destination. In the animated television series Futurama, set in the 31st century, large pneumatic tubes are used in cities for transporting people, whilst smaller ones are used to transport mail. The tubes in Futurama are also used to depict the endless confusion of bureaucracy: an immense network of pneumatic tubes connects all offices in New New York City to the "Central Bureaucracy", with all the capsules being deposited directly into a huge pile in the main filing room, with no sorting or organization.

In Kurt Vonnegut's Slaughterhouse-Five pneumatic tubes are used as a way to transport information from one place to the next when covering news articles.

[edit] See alsoA compressed-air vehicle is powered by an air engine, using compressed air, which is stored in a tank. Instead of mixing fuel with air and burning it in the engine to drive pistons with hot expanding gases, compressed air vehicles (CAV) use the expansion of compressed air to drive their pistons. One manufacturer claims to have designed an engine that is 90 percent efficient.[1]

Compressed air propulsion may also be incorporated in hybrid systems, e.g., battery electric propulsion and fuel tanks to recharge the batteries. This kind of system is called a hybrid-pneumatic electric propulsion. Additionally, regenerative braking can also be used in conjunction with this system.

Contents [hide]
1 Technology
1.1 Engine
1.2 Tanks
1.3 Compressed air
1.4 Emission output
2 History
3 Advantages
4 Disadvantages
5 Possible improvements
6 Vehicles
6.1 Mopeds
6.2 Cars
6.3 Buses
6.4 Locomotives
6.5 Trams
6.6 Watercraft and aircraft
7 See also
8 External links
9 References

[edit] Technology

[edit] Engine
Main article: Compressed air engine
One can buy the vehicle with the engine or buy an engine to be installed in the vehicle. Typical air engines use one or more expander pistons. In some applications it is advantageous to heat the air, or the engine, to increase the range or power.

[edit] Tanks
Main article: Compressed air tank
The tanks must be designed to safety standards appropriate for a pressure vessel, such as ISO 11439.[2]

The storage tank may be made of:

steel,
aluminium,
carbon fiber,
Kevlar,
other materials, or combinations of the above.
The fiber materials are considerably lighter than metals but generally more expensive. Metal tanks can withstand a large number of pressure cycles, but must be checked for corrosion periodically.

One company stores air in tanks at 4,500 pounds per square inch (about 30 MPa) and hold nearly 3,200 cubic feet(around 90 cubic metres) of air.[3]

The tanks may be refilled at a service station equipped with heat exchangers, or in a few hours at home or in parking lots, plugging the car into the electric grid via an on-board compressor. The cost of driving such a car is typically projected to be around €0.75 per 100 km, with a complete refill at the "tank-station" at about US$3.

[edit] Compressed air
Main article: Compressed air
Compressed air has a low energy density. In 300 bar containers, about 0.1 MJ/L and 0.1 MJ/kg is achievable, comparable to the values of electrochemical lead-acid batteries. While batteries can somewhat maintain their voltage throughout their discharge and chemical fuel tanks provide the same power densities from the first to the last litre, the pressure of compressed air tanks falls as air is drawn off. A consumer-automobile of conventional size and shape typically consumes 0.3-0.5 kWh (1.1-1.8 MJ) at the drive shaft[4] per mile of use, though unconventional sizes may perform with significantly less.

[edit] Emission output
Like other non-combustion energy storage technologies, an air vehicle displaces the emission source from the vehicle's tail pipe to the central electrical generating plant. Where emissions-free sources are available, net production of pollutants can be reduced. Emission control measures at a central generating plant may be more effective and less costly than treating the emissions of widely-dispersed vehicles.

Since the compressed air is filtered to protect the compressor machinery, the air discharged has less suspended dust in it, though there may be carry-over of lubricants used in the engine.

[edit] History
Compressed air has been used since the 19th century to power mine locomotives and trams in cities such as Paris (via a central, city-level, compressed air energy distribution system), and was previously the basis of naval torpedo propulsion.

In 1863, Jules Verne wrote a novel called Paris in the 20th Century about a world of glass skyscrapers, high-speed trains, and air-powered automobiles.

In 1903, the Liquid Air Company located in London England manufactured a number of compressed air and liquified air cars. The major problem with these cars and all compressed air cars is the lack of torque produced by the "engines" and the cost of compressing the air. Reference: http://www.didik.com/ev_hist.htm

Recently several companies have started to develop compressed air cars, although none have been released to the public, or have been tested by third parties.

[edit] Advantages
The advantages are well publicised since the developers need to make their machines attractive to investors. Compressed-air vehicles are comparable in many ways to electric vehicles, but use compressed air to store the energy instead of batteries. Their potential advantages over other vehicles include:

Much like electrical vehicles, air powered vehicles would ultimately be powered through the electrical grid. Which makes it easier to focus on reducing pollution from one source, as opposed to the millions of vehicles on the road.
Transportation of the fuel would not be required due to drawing power off the electrical grid. This presents significant cost benefits. Pollution created during fuel transportation would be eliminated.
Compressed air technology reduces the cost of vehicle production by about 20%, because there is no need to build a cooling system, fuel tank, spark plugs or silencers.[5]
Air, on its own, is non-flammable.
High torque for minimum volume.
The mechanical design of the engine is simple and robust.
Low manufacture and maintenance costs as well as easy maintenance.
Compressed-air tanks can be disposed of or recycled with less pollution than batteries.
Compressed-air vehicles are unconstrained by the degradation problems associated with current battery systems.[3]
The tank may be able to be refilled more often and in less time than batteries can be recharged, with re-fueling rates comparable to liquid fuels.
Lighter vehicles would mean less abuse on roads. Resulting in longer lasting roads.
The price of fueling air powered vehicles will be significantly cheaper than current fuels.

[edit] Disadvantages
Disadvantages of compressed-air vehicles are less well known, since the vehicles are currently at the pre-production stage and have not been extensively tested by independent observers.

Some Disadvantages could include:

Compressed air vehicles likely will be less robust than typical vehicles of today. Which poses a danger to users of compressed air vehicles sharing the road with larger, heavier and more rigid vehicles.
When the air is expanded in the engine, it will cool down via adiabatic cooling and lose pressure thus its ability to do work at colder temperatures. It is difficult to maintain or restore the air temperature by simply using a heat exchanger with ambient heat at the high flow rates used in a vehicle, thus the ideal isothermic energy capacity of the tank will not be realised. Cold temperatures will also encourage the engine to ice up.

[edit] Possible improvements
Compressed-air vehicles operate to a thermodynamic process as air cools down when expanding and heats up when being compressed. As it is not possible in practice to use a theoretically ideal process, losses occur and improvements may involve reducing these, e.g., by using large heat exchangers in order to use heat from the ambient air and at the same time provide air cooling in the passenger compartment. At the other end, the heat produced during compression can be stored in water systems, physical or chemical systems and reused later.

[edit] Vehicles

[edit] Mopeds[edit] Compressed Air Brake System
A "Compress Air Brake System" is a different air brake used for trucks, consisting of a standard disc or drum brake arrangement using compressed air in place of hydraulic fluid. Most types of truck air brakes are drum units, though there is an increasing trend towards the use of disc brakes in this application. The compressed air brakes system works by drawing filtered air from the atmosphere, compressing it, and holding it in high-pressure reservoirs at around 120 PSI. When needed for braking, this high pressure air is routed to the operating cylinders on the brakes, which actuate the braking hardware and slow the vehicle. Air brakes use compressed air to maximise braking forces.

[edit] Design and Function
A compressed air brake system is divided into a supply system and a control system. The supply system compresses, stores and supplies high-pressure air to the control system as well as to additional air operated auxiliary truck systems (gearbox shift control, clutch pedal air assistance servo, etc.).

[edit] Supply system

" Over simplified" air brake diagram on a commercial road vehicle (does not show all air reservoirs and all applicable air valves).The air compressor is driven off of the engine either by crankshaft pulley via a belt or directly off of the engine timing gears. It is lubricated and cooled by the engine lubrication and cooling systems. Compressed air is first routed through a cooling coil and into an air dryer the dryer device which removes m
oisture and oil impurities and also may include a pressure regulator ,safety valve and a smaller purge reservoir. As an alternative
to the air dryer, the supply system can be equipped with an anti freeze device and oil separator. The compressed air is then stored
in a reservoir (also called a primary tank) from which it is then distributed via a four way protection valve into the front and rear brake circuit air reservoir, a parking brake reservoir and an auxiliary air supply distribution point. The system also includes various check, pressure limiting, drain and safety valves.

[edit] Control system
The control system is further divided into two service brake circuits: the parking brake circuit and the trailer brake circuit. This dual brake circuit is further split into front and rear wheel circuits which receive compressed air from their individual reservoirs for added safety in case of an air leak. The service brakes are applied by means of a brake pedal air valve which regulates both circuits. The parking brake is the air operated spring brake type where its applied by spring force in the spring brake cylinder and released by compressed air via hand control valve. The trailer brake consists of a direct two line system: the supply line (marked red) and the separate control or service line (marked blue). The supply line receives air from the prime mover park brake air tank via a park brake relay valve and the control line is regulated via the trailer brake relay valve. The operating signals for the relay are provided by the prime mover brake pedal air valve, trailer service brake hand control (subject to a country's relevant heavy vehicle legislation) and the prime mover park brake hand control.

Park brake valve
Spring brake cylinder
Air brake foot valve
Trailer brake relay valve

Truck air compressor
Air dryer
Air brake relay valve
Four way protection valve

[edit] Aerodynamic Occlusion as Vehicle Air Brake
This example of the air brake consists of a physical structure on the exterior of a vehicle that will increase the vehicle's drag coefficient, and therefore slow it down. Air brakes of this sort are ineffective at normal road vehicle speeds, and therefore are reserved for vehicles which need to quickly decelerate from high speeds, such as race and high performance sports cars.

The Bugatti Veyron features a rear spoiler which is able to automatically move from the standard wing angle to nearly 70 degrees under high speed braking. Top Fuel Dragsters use this same concept of aerodynamic occlusion via a parachute.

[edit] See also
Air brake
Knorr-Bremse
Ozone cracking
Polymer degradation
Railway air brake

Tools
Impact wrenches, drills, die grinders, dental drills and other pneumatic tools use a variety of air engines or motors. These include vane type pumps, turbines and pistons.

[edit] Torpedoes
Most successful early forms of self propelled torpedoes used high pressure compressed air, although this was superseded by internal or external combustion engines, steam engines, or electric motors.

[edit] Railways
Compressed air engines were used in trams and shunters, and eventually found a successful niche in mining locomotives, although eventually they were replaced by electric trains, underground[1]. Over the years designs increased in complexity, resulting in a triple expansion engine with air to air reheaters between each stage [2].

[edit] Aircraft
Transport category airplanes, such as commercial airliners, use compressed air starters to start the main engines. The air is supplied by the load compressor of the aircraft's auxiliary power unit, or by ground equipment.

[edit] Automotive
Main article: Compressed air vehicle
There is currently some interest in developing air cars. Several engines have been proposed for these, although none have demonstrated the performance and long life needed for personal transport.

[edit] Energine
The Energine Corporation is a South Korean company that delivers fully-assembled cars running on a hybrid compressed air and electric engine. The compressed-air engine is used to activate an alternator, which extends the autonomous operating capacity of the car.

[edit] EngineAir
EngineAir, an Australian company, is making a rotary engine powered by compressed air, called The Di Pietro motor. The Di Pietro motor concept is based on a rotary piston. Different from existing rotary engines, the Di Pietro motor uses a simple cylindrical rotary piston (shaft driver) which rolls, with little friction, inside the cylindrical stator. [3]

It can be used in boat, cars, carriers and other vehicles. Only 1 psi (˜ 6,8 kPa) of pressure is needed to overcome the friction. [4] [5]

[edit] K'Airmobiles
K'Airmobiles vehicles use a compressed-air engine known as the K'Air, developed in France by a small group of researchers

These engines have a consumption of compressed air of less than 120 L/min., although developing a dynamic push able to reach 4kN.

The technical concept of the K'Air pneumatic engines returns to direct conversion of what makes the fundamental characteristic of compressed air, namely:

the pushing force of compressed air is exclusively exploited for conversion into kinetic energy of translation,
itself is simultaneously converted into induced power of rotation of the axis and
thus gives to the engine a particularly imposing torque while needing only a very low “fuel” consumption.
To simplify, one can compare the principle to that of the rotary jacks:

the energy of the fluid (compressed air) is directly transformed into rotational movement;
the double-acting jacks involve a pinion-toothed rack system;
the cyclic angle of rotation can vary between 90 and 360°;
it supports hydraulic supercharging systems.

[edit] MDI
Main article: Motor Development International
In the original Nègre air engine, one piston compresses air from the atmosphere to mix with the stored compressed air (which will cool drastically as it expands). This mixture drives the second piston, providing the actual engine power. MDI's engine works with constant torque, and the only way to change the torque to the wheels is to use a pulley transmission of constant variation, losing some efficiency. When vehicle is stopped, MDI's engine had to be on and working, losing energy. In 2001-2004 MDI switched to a design similar to that described in Regusci's patents (see below), which date back to 1990[6].

[edit] Quasiturbine
Main article: Quasiturbine
The Pneumatic Quasiturbine engine is a compressed air pistonless rotary engine using a rhomboidal-shaped rotor whose sides are hinged at the vertices.

The Quasiturbine has demonstrated as a pneumatic engine using stored compressed air [7].

It can also take advantage of the energy amplification possible from using available external heat, such as solar energy. [8]

The Quasiturbine rotates from pressure as low as 0.1 atm.

Since the Quasiturbine is a pure expansion engine (which the Wankel is not, nor are most other rotary engines), it is well suitable as compressed fluid engine - Air engine or air motor. [8]

[edit] Regusci
Armando Regusci's version[9] of the air engine couples the transmission system directly to the wheel, and has variable torque from zero to the maximum, enhancing efficiency. Regusci's patents date back to 1990[6],

[edit] Team Psycho-Active
Psycho-Active is developing a multi-fuel/air-hybrid chassis which is intended to serve as the foundation for a line of automobiles. Claimed performance is 50 hp/litre [10]

[edit] Karts
At least one Kart has been powered by a quasiturbine.[11]

[edit] Efficient air engines
One could make the compressed air engines much more efficient than they are now (15%) by for example:

Using the heat energy from the compressor (ALL energy used to run the compressor is converted to heat due to friction),
shut down the air after a while ("cutoff"),
Expand the air in several various stages and heat the air again between the expansions by ordinary air (in a heat exchanger),

[edit] See also
Angelo Di Pietro (inventor)
Compressed air energy storage
Compressor
Kit car
Pump
From Wikipedia, the free encyclopedia
Jump to: navigation, search
This article is about a mechanical device. For other uses, see Pump (disambiguation).
For information on Wikipedia project-related discussions, see Wikipedia:Village pump.

A small, electrically powered pump
A large, electrically driven pump (electropump) for waterworks near the Hengsteysee, Germany.A pump is a device used to move fluids, such as gases, liquids or slurries. A pump displaces a volume by physical or mechanical action. One common misconception about pumps is the thought that they create pressure. Pumps alone do not create pressure they only displace fluid causing a flow. Adding resistance to flow causes pressure.

The earliest type of pump was the Archimedes' screw, first used by Sennacherib, King of Assyria, for the water systems at the Hanging Gardens of Babylon and Nineveh in the 7th century BC, and later described in more detail by Archimedes in the 3rd century BC.[1] In the 13th century AD, al-Jazari described and illustrated different types of pumps, including a reciprocating pump, double-action pump, suction pump, and piston pump.[2][3]

In Indian mythology, Lord Krishna playfully splashed colors on Gopees using a "Pichkaaree", which was, and is even now, a reciprocating hand pump. Hence historically "Pichkaaree" should be recognized as the first pump, ever devised.

Contents [hide]
1 Types
1.1 Positive displacement pumps
1.1.1 Roots-type pumps
1.1.2 Reciprocating-type pumps
1.1.3 Compressed-air-powered double-diaphragm pumps
1.2 Kinetic Pumps
2 Application
3 Specifications
4 Pumps as public water supplies
5 See also
6 Gallery
7 References
8 Further reading

[edit] Types
Pumps fall into two major groups: positive displacement pumps and rotodynamic pumps . Their names describe the method for moving a fluid.

[edit] Positive displacement pumps

A lobe pump
Hand-operated, reciprocating, positive displacement, water pump in Košice-Tahanovce, Slovakia (walking beam pump).
Mechanism of a scroll pumpA positive displacement pump causes a fluid to move by trapping a fixed amount of it then forcing (displacing) that trapped volume into the discharge pipe. A positive displacement pump can be further classified as either

a rotary-type, for example, the lobe, external gear, internal gear, screw, shuttle block, flexible vane or sliding vane pumps,
the Wendelkolben pump or the helical twisted Roots pump.
the liquid ring vacuum pump

[edit] Roots-type pumps
The low pulsation rate and gentle performance of this Roots-type positive displacement pump is achieved due to a combination of its two 90° helical twisted rotors, and a triangular shaped sealing line configuration, both at the point of suction and at the point of discharge. This design produces a continuous and non-vorticuless flow with equal volume. High capacity industrial "air compressors" have been designed to employ this principle as well as most "superchargers" used on internal combustion engines.

[edit] Reciprocating-type pumps
Reciprocating-type pumps use a piston and cylinder arrangement with suction and discharge valves integrated into the pump. Pumps in this category range from having "simplex" one cylinder, to in some cases "quad" four cylinders or more. Most reciprocating-type pumps are "duplex" (two) or "triplex" (three) cylinder. Furthermore, they are either "single acting" independent suction and discharge strokes or "double acting" suction and discharge in both directions. The pumps can be powered by air, steam or through a belt drive from an engine or motor. This type of pump was used extensively in the early days of steam propulsion (19th century) as boiler feed water pumps. Though still used today, reciprocating pumps are typically used for pumping highly viscous fluids including concrete and heavy oils.

[edit] Compressed-air-powered double-diaphragm pumps
Another modern application of positive displacement pumps are compressed-air-powered double-diaphragm pumps. Run on compressed air these pumps are intrinsically safe by design, although all manufacturers offer ATEX certified models to comply with industry regulation. Commonly seen in all areas of industry from shipping to process, SandPiper, Wilden Pumps or ARO are generally the larger of the brands. They are relatively inexpensive and can be used for almost any duty from pumping water out of bunds, to pumping hydrochloric acid from secure storage (dependant on how the pump is manufactured - elastomers / body construction). Suction is normally limited to roughly 6m although heads can be almost unlimited.

[edit] Kinetic Pumps
This section may require cleanup to meet Wikipedia's quality standards. Please improve this section if you can. (September 2008)

Continuous energy
Conversion of added energy to increase in kinetic energy (increase in velocity)
Conversion of increased velocity to increase in pressure
Conversion of Kinetic head to Pressure Head.
Meet all heads like Kinetic , Potential, and Pressure

[edit] Application

Metering pump for gasoline and additivesPumps are used throughout society for a variety of purposes. Early applications includes the use of the windmill or watermill to pump water. Today, the pump is used for irrigation, water supply, gasoline supply, air conditioning systems, refrigeration (usually called a compressor), chemical movement, sewage movement, flood control, marine services, etc.

Because of the wide variety of applications, pumps have a plethora of shapes and sizes: from very large to very small, from handling gas to handling liquid, from high pressure to low pressure, and from high volume to low volume.

Liquid and slurry pumps can lose prime and this will require you to prime the pump by adding liquid to the pump and inlet pipes to get the pump started. Loss of "prime" is usually due to ingestion of air into the pump. The clearances and displacement ratios in pumps used for liquids and other more viscus fluids cannot displace the air due to its lower density.

[edit] Specifications
Pumps are commonly rated by horsepower, flow rate, outlet pressure in feet of head, inlet suction in suction head in feet. Feet is the number of feet the pump can raise or lower a column of water at atmospheric pressure.

[edit] Pumps as public water supplies
One sort of pump once common worldwide was a hand-powered water pump over a water well where people could work it to extract water, before most houses had individual water supplies.

From this came the expression "parish pump" for "the sort of matter chattered about by people when they meet when they go to get water", "matter of only local interest". However water from pitcher pumps are more prone to contamination since it is drawn directly from the soil and does not undergo filtration, this might cause gastrointestinal related diseases.

Today, hand operated village pumps are considered the most sustainable low cost option for safe water supply in resource poor settings, often in rural areas in developing countries. A hand pump opens access to deeper groundwater that is often not polluted and also improves the safety of a well by protecting the water source from contaminated buckets. Pumps like the Afridev pump are designed to be cheap to build and install, and easy to maintain with simple parts. However, scarcity of spare parts for these type of pumps in some regions of Africa has diminished their utility for these areas.[citation needed]

[edit] See also
Affinity laws
Airlift pump
Archimedes' screw
Balancing machine
Axial flow pump
Beam pump and walking beam pump
Bicycle pump
Boiler feedwater pump
Breast pump
Centrifugal pump
Chain pumps
Circulator pump
Concrete pump
Condensate pump
Cyclic pump
Diving pump
Diaphragm pump
Eductor-jet pump
Electroosmotic pump
Fire pump and Jockey pump
Gas compressors
Gear pump
Gerotor
Hand pump
Hydraulic ram
Metering pump
Oil pump
Peristaltic pump
Progressive cavity pump (also known as; progressing cavity, eccentric screw or Mono pump)
Pumping station
Pumpjack (oil pump)
Rope pump
Roundabout PlayPump
Scroll pump, most used in scroll compressors
Tesla turbine
Treadle pump
Turbopump
Vacuum pump
Well water pump
Wind pump
History
Water wheels have been used for thousands of years for industrial power. Their main shortcoming is size, which limits the flow rate and head that can be harnessed. The migration from water wheels to modern turbines took about one hundred years. Development occurred during the Industrial revolution, using scientific principles and methods. They also made extensive use of new materials and manufacturing methods developed at the time.

[edit] Swirl
The word turbine was coined by the French engineer Claude Bourdin in the early 19th century and is derived from the Latin word for "whirling" or a "vortex". The main difference between early water turbines and water wheels is a swirl component of the water which passes energy to a spinning rotor. This additional component of motion allowed the turbine to be smaller than a water wheel of the same power. They could process more water by spinning faster and could harness much greater heads. (Later, impulse turbines were developed which didn't use swirl).

[edit] Time line

A Francis turbine runner, rated at nearly one million hp (750 MW), being installed at the Grand Coulee Dam
A propeller-type runner rated 28,000 hp (21 MW)As early as the 1st century BC, the ancient Greeks and Romans used the waterwheel, an ancestor of water turbines,to grind grain.[1]

A primitive water turbine, which had water wheels with curved blades onto which water flow was directed axially, for use in a watermill, was first described in an Arabic text written in the 9th century, during the Arab Agricultural Revolution.[2]

Ján Andrej Segner developed a reactive water turbine in the mid-1700s. It had a horizontal axis and was a precursor to modern water turbines. It is a very simple machine that is still produced today for use in small hydro sites. Segner worked with Euler on some of the early mathematical theories of turbine design.

In 1820, Jean-Victor Poncelet developed an inward-flow turbine.

In 1826 Benoit Fourneyron developed an outward-flow turbine. This was an efficient machine (~80%) that sent water through a runner with blades curved in one dimension. The stationary outlet also had curved guides.

In 1844 Uriah A. Boyden developed an outward flow turbine that improved on the performance of the Fourneyron turbine. Its runner shape was similar to that of a Francis turbine.

In 1849, James B. Francis improved the inward flow reaction turbine to over 90% efficiency. He also conducted sophisticated tests and developed engineering methods for water turbine design. The Francis turbine, named for him, is the first modern water turbine. It is still the most widely used water turbine in the world today.The Francis turbine is also called as Radial flow Turbine.In which water flows from outercircumference towards the centre of runner.

Inward flow water turbines have a better mechanical arrangement and all modern reaction water turbines are of this design. As the water swirls inward, it accelerates, and transfers energy to the runner. Water pressure decreases to atmospheric, or in some cases subatmospheric, as the water passes through the turbine blades and loses energy.

Around 1890, the modern fluid bearing was invented, now universally used to support heavy water turbine spindles. As of 2002, fluid bearings appear to have a mean time between failures of more than 1300 years.

Around 1913, Viktor Kaplan created the Kaplan turbine, a propeller-type machine. It was an evolution of the Francis turbine but revolutionized the ability to develop low-head hydro sites.

[edit] A new concept

Figure from Pelton's original patent (October 1880)Main article: Pelton wheel
All common water machines until the late 19th century (including water wheels) were reaction machines; water pressure head acted on the machine and produced work. A reaction turbine needs to fully contain the water during energy transfer.

In 1866, California millwright Samuel Knight invented a machine that worked off a completely different concept[3][4]. Inspired by the high pressure jet systems used in hydraulic mining in the gold fields, Knight developed a bucketed wheel which captured the energy of a free jet, which had converted a high head (hundreds of vertical feet in a pipe or penstock) of water to kinetic energy. This is called an impulse or tangential turbine. The water's velocity, roughly twice the velocity of the bucket periphery, does a u-turn in the bucket and drops out of the runner at low velocity.

In 1879, Lester Pelton(1829-1908), experimenting with a Knight Wheel, developed a double bucket design, which exhausted the water to the side, eliminating some energy loss of the Knight wheel which exhausted some water back against the center of the wheel. In about 1895, William Doble improved on Pelton's half-cylindrical bucket form with an elliptical bucket that included a cut in it to allow the jet a cleaner bucket entry. This is the modern form of the Pelton turbine which today achieves up to 92% efficiency. Pelton had been quite an effective promoter of his design and although Doble took over the Pelton company he did not change the name to Doble because it had brand name recognition.

Turgo and Crossflow turbines were later impulse designs.

[edit] Theory of operation
Flowing water is directed on to the blades of a turbine runner, creating a force on the blades. Since the runner is spinning, the force acts through a distance (force acting through a distance is the definition of work). In this way, energy is transferred from the water flow to the turbine.

Water turbines are divided into two groups; reaction turbines and impulse turbines.

The precise shape of water turbine blades is a function of the supply pressure of water, and the type of impeller selected.

[edit] Reaction turbines
Reaction turbines are acted on by water, which changes pressure as it moves through the turbine and gives up its energy. They must be encased to contain the water pressure (or suction), or they must be fully submerged in the water flow.

Newton's third law describes the transfer of energy for reaction turbines.

Most water turbines in use are reaction turbines. They are used in low and medium head applications.

[edit] Impulse turbines
Impulse turbines change the velocity of a water jet. The jet impinges on the turbine's curved blades which change the direction of the flow. The resulting change in momentum (impulse) causes a force on the turbine blades. Since the turbine is spinning, the force acts through a distance (work) and the diverted water flow is left with diminished energy.

Prior to hitting the turbine blades, the water's pressure (potential energy) is converted to kinetic energy by a nozzle and focused on the turbine. No pressure change occurs at the turbine blades, and the turbine doesn't require a housing for operation.

Newton's second law describes the transfer of energy for impulse turbines.

Impulse turbines are most often used in very high head applications.

[edit] Power
The power available in a stream of water is;

where:

P = power (J/s or watts)
? = turbine efficiency
? = density of water (kg/m³)
g = acceleration of gravity (9.81 m/s²)
h = head (m). For still water, this is the difference in height between the inlet and outlet surfaces. Moving water has an additional component added to account for the kinetic energy of the flow. The total head equals the pressure head plus velocity head.
= flow rate (m³/s)

[edit] Pumped storage
Some water turbines are designed for pumped storage hydroelectricity. They can reverse flow and operate as a pump to fill a high reservoir during off-peak electrical hours, and then revert to a turbine for power generation during peak electrical demand. This type of turbine is usually a Deriaz or Francis in design.

[edit] Efficiency
Large modern water turbines operate at mechanical efficiencies greater than 90% (not to be confused with thermodynamic efficiency).

[edit] Types of water turbines
Reaction turbines:

Francis
Kaplan, Propeller, Bulb, Tube, Straflo
Tyson
Water wheel
Archimedean screw turbine
Impulse turbines:

Pelton
Turgo
Michell-Banki (also known as the Crossflow or Ossberger turbine)

[edit] Design and application
Turbine selection is based mostly on the available water head, and less so on the available flow rate. In general, impulse turbines are used for high head sites, and reaction turbines are used for low head sites. Kaplan turbines with adjustable blade pitch are well-adapted to wide ranges of flow or head conditions, since their peak efficiency can be achieved over a wide range of flow conditions.

Small turbines (mostly under 10 MW) may have horizontal shafts, and even fairly large bulb-type turbines up to 100 MW or so may be horizontal. Very large Francis and Kaplan machines usually have vertical shafts because this makes best use of the available head, and makes installation of a generator more economical. Pelton wheels may be either vertical or horizontal shaft machines because the size of the machine is so much less than the available head. Some impulse turbines use multiple water jets per runner to increase specific speed and balance shaft thrust.

[edit] Typical range of heads
Hydraulic wheel turbine 0.2 < H < 4 (H = head in m)
Archimedes' screw turbine 1 < H < 10
Kaplan 2 < H < 40
Francis 10 < H < 350
Pelton 50 < H < 1300
Turgo 50 < H < 250

[edit] Specific speed
Main article: Specific speed
The specific speed ns of a turbine characterizes the turbine's shape in a way that is not related to its size. This allows a new turbine design to be scaled from an existing design of known performance. The specific speed is also the main criteria for matching a specific hydro site with the correct turbine type.

[edit] Affinity laws
Affinity Laws allow the output of a turbine to be predicted based on model tests. A miniature replica of a proposed design, about one foot (0.3 m) in diameter, can be tested and the laboratory measurements applied to the final application with high confidence. Affinity laws are derived by requiring similitude between the test model and the application.

Flow through the turbine is controlled either by a large valve or by wicket gates arranged around the outside of the turbine runner. Differential head and flow can be plotted for a number of different values of gate opening, producing a hill diagram used to show the efficiency of the turbine at varying conditions.

[edit] Runaway speed
The runaway speed of a water turbine is its speed at full flow, and no shaft load. The turbine will be designed to survive the mechanical forces of this speed. The manufacturer will supply the runaway speed rating.

[edit] Maintenance

A Francis turbine at the end of its life showing cavitation pitting, fatigue cracking and a catastrophic failure. Earlier repair jobs that used stainless steel weld rods are visible.Turbines are designed to run for decades with very little maintenance of the main elements; overhaul intervals are on the order of several years. Maintenance of the runners and parts exposed to water include removal, inspection, and repair of worn parts.

Normal wear and tear includes pitting from cavitation, fatigue cracking, and abrasion from suspended solids in the water. Steel elements are repaired by welding, usually with stainless steel rod. Damaged areas are cut or ground out, then welded back up to their original or an improved profile. Old turbine runners may have a significant amount of stainless steel added this way by the end of their lifetime. Elaborate welding procedures may be used to achieve the highest quality repairs.[5]

Other elements requiring inspection and repair during overhauls include bearings, packing box and shaft sleeves, servomotors, cooling systems for the bearings and generator coils, seal rings, wicket gate linkage elements and all surfaces. [6]

[edit] Environmental impact
Water turbines are generally considered a clean power producer, as the turbine causes essentially no change to the water. They use a renewable energy source and are designed to operate for decades. They produce significant amounts of the world's electrical supply.

Historically there have also been negative consequences, mostly associated with the dams normally required for power production. Dams alter the natural ecology of rivers, potentially killing fish, stopping migrations, and disrupting peoples' livelihoods. For example, American Indian tribes in the Pacific Northwest had livelihoods built around salmon fishing, but aggressive dam-building destroyed their way of life. Dams also cause less obvious, but potentially serious consequences, including increased evaporation of water (especially in arid regions), build up of silt behind the dam, and changes to water temperature and flow patterns. Some people[who?] believe that it is possible to construct hydropower systems that divert fish and other organisms away from turbine intakes without significant damage or loss of power; historical performance of diversion structures has been poor. In the United States, it is now illegal to block the migration of fish so fish ladders must be provided by dam builders. The actual performance of fish ladders is often poor.[citation needed]

[edit] See also
Sustainable development portal
Banki turbine
Gorlov helical turbine
Hydroelectricity
Hydropower
Turbine
Water Wheel

[edit] References
^ Reynolds, Terry S. (2002). Stronger Than a Hundred Men: A History of the Vertical Water Wheel. Baltimore MD: Johns Hopkins University Press. pp. 16. ISBN 0801872480.
^ Donald Routledge Hill, "Mechanical Engineering in the Medieval Near East", Scientific American, May 1991, p. 64-69. (cf. Donald Routledge Hill, Mechanical Engineering)
^ W. A. Doble, The Tangential Water Wheel, Transactions of the American Institute of Mining Engineers, Vol. XXIX, 1899.
^ W. F. Durrand, The Pelton Water Wheel, Stanford University, Mechanical Engineering, 1939.
^ Cline, Roger:Mechanical Overhaul Procedures for Hydroelectric Units (Facilities Instructions, Standards, and Techniques, Volume 2-7); United States Department of the Interior Bureau of Reclamation, Denver, Colorado, July 1994 (800KB pdf).
^ United States Department of the Interior Bureau of Reclamation; Duncan, William (revised April 1989): Turbine Repair (Facilities Instructions, Standards & Techniques, Volume 2-5) (1.5 MB pdf).

[edit] External links
Introductory turbine math
European Union publication, Layman's hydropower handbook,12 MB pdf
"Selecting Hydraulic Reaction Turbines", US Bureau of Reclamation publication, 48 MB pdf
"Laboratory for hydraulique machines", Lausanne (Switzerland)
DoradoVista, Small Hydro Power Information
Retrieved from "http://en.wikipedia.org/wiki/Water_turbine"
Category: Water turbines
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Accumulator (energy)
From Wikipedia, the free encyclopedia
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An accumulator is an apparatus by means of which energy can be stored, such as a rechargeable battery or a hydraulic accumulator. Such devices may be electrical, fluidic or mechanical and are sometimes used to convert a small continuous power source into a short surge of energy or vice versa. Other examples of accumulators include capacitors, compulsators, steam accumulator, wave energy machines, pumped-storage hydroelectric plants.

A hydraulic accumulator is an energy storage device. It is a pressure storage reservoir in which a non-compressible hydraulic fluid is held under pressure by an external source. That external source can be a spring, a raised weight, or a compressed gas. The main reasons that an accumulator is used in a hydraulic system are so that the pump doesn't need to be so large to cope with extremes of demand, so that the supply circuit can respond more quickly to any temporary demand and to smooth pulsations.

Compressed gas accumulators are by far the most common type. These are also called hydro-pneumatic accumulators.

Contents [hide]
1 Types of accumulator
1.1 Raised weight
1.2 Compressed gas (or gas-charged) accumulator
1.3 Spring type
1.4 Metal bellows type
2 Functioning of an accumulator
3 References
4 See also
5 External links

[edit] Types of accumulator
An accumulator is basically an energy storage device.

[edit] Raised weight

Hydraulic engine house, Bristol HarbourA raised weight accumulator consists of a vertical cylinder containing fluid connected to the hydraulic line. The cylinder is closed by a piston on which a series of weights are placed that exert a downward force on the piston and thereby energizes the fluid in the cylinder. In contrast to compressed gas and spring accumulators, this type delivers a nearly constant pressure, regardless of the volume of fluid in the cylinder, until it is empty. (The pressure will decline somewhat as the cylinder is emptied due to the decline in weight of the remaining fluid.)

A working example of this type of accumulator may be found at the hydraulic engine house, Bristol Harbour.[1] The external accumulator was added around 1920. The water is pumped from the harbour into a header tank and then fed by gravity to the pumps. The working pressure is 750 psi (5.2 MPa) which is used to power the cranes, bridges and locks of Bristol Harbour.

The original operating mechanism of Tower Bridge, London, also used this type of accumulator. Although no longer in use, the accumulators may still be seen in situ in the bridge's museum.

London had an extensive public hydraulic power system from the mid-nineteenth century finally closing in the 1970s with 5 hydraulic power stations, operated by the London Hydraulic Power Company. Railway goods yards and docks often had their own separate system, a particularly delightful example of an early accumulator, dating from 1869 being at the Regent's Canal Dock of the Regent's Canal Company at Limehouse, London. The artifact has been converted into a visitor attraction which is open yearly during London Open House weekend, usually the third weekend in September.

[edit] Compressed gas (or gas-charged) accumulator
A compressed gas accumulator consists of a cylinder with two chambers that are separated by an elastic diaphragm, a totally enclosed bladder, or a floating piston. One chamber contains hydraulic fluid and is connected to the hydraulic line. The other chamber contains an inert gas under pressure (typically nitrogen) that provides the compressive force on the hydraulic fluid. Inert gas is used because oxygen and oil can form an explosive mixture when combined under high pressure. As the volume of the compressed gas changes the pressure of the gas, and the pressure on the fluid, changes inversely.

[edit] Spring type
A spring type accumulator is similar in operation to the gas-charged accumulator above, except that a heavy spring (or springs) is used to provide the compressive force. According to Hooke's law the magnitude of the force exerted by a spring is linearly proportional to its extension. Therefore as the spring compresses, the force it exerts on the fluid is increased.

[edit] Metal bellows type
The metal bellows accumulators function similarly to the compressed gas type, except the elastic diaphragm or floating piston is replaced by a hermetically sealed welded metal bellows. Fluid may be internal or external to the bellows. The advantages to the metal bellows type include exceptionally low spring rate, allowing the gas charge to do all the work with little change in pressure from full to empty, and a long stroke relative to solid (empty) height, which gives maximum storage volume for a given container size. The welded metal bellows accumulator provides an exceptionally high level of accumulator performance, and can be produced with a broad spectrum of alloys resulting in a broad range of fluid compatibility. Another advantage to this type is that it does not face issues with high pressure operation, thus allowing more energy storage capacity.

[edit] Functioning of an accumulator
In modern, often mobile, hydraulic systems the preferred item is a gas charged accumulator, but simple systems may be spring-loaded. There may be more than one accumulator in a system. The exact type and placement of each may be a compromise due to its effects and the costs of manufacture.

An accumulator is placed close to the pump with a non-return valve preventing flow back to it. In the case of piston-type pumps this accumulator is placed in the best place to absorb pulsations of energy from the multi-piston pump. It also helps protect the system from fluid hammer. This protects system components, particularly pipework, from both potentially destructive forces.

An additional benefit is the additional energy that can be stored while the pump is subject to low demand. The designer can use a smaller-capacity pump. The large excursions of system components, such as landing gear on a large aircraft, that require a considerable volume of fluid can also benefit from one or more accumulators. These are often placed close to the demand to help overcome restrictions and drag from long pipework runs. The outflow of energy from a discharging accumulator is much greater, for a short time, than even large pumps could generate.

An accumulator can maintain the pressure in a system for periods when there are slight leaks without the pump being cycled on and off constantly. When temperature changes cause pressure excursions the accumulator helps absorb them. Its size helps absorb fluid that might otherwise be locked in a small fixed system with no room for expansion due to valve arrangement.

The gas precharge in an accumulator is set so that the separating bladder, diaphragm or piston does not reach or strike either end of the operating cylinder. The design precharge normally ensures that the moving parts do not foul the ends or block fluid passages. Poor maintenance of precharge can destroy an operating accumulator. A properly designed and maintained accumulator should operate trouble-free for years.

[edit] References
^ "hydraulic engine house". Images of England. http://www.imagesofengland.org.uk/search/details.aspx?id=380746. Retrieved on 2006-08-18.
For a hammer powered by water, see Trip hammer.
Water hammer (or, more generally, fluid hammer) is a pressure surge or wave resulting when a fluid in motion is forced to stop or change direction suddenly (momentum change). Water hammer commonly occurs when a valve is closed suddenly at an end of a pipeline system, and a pressure wave propagates in the pipe.

Contents [hide]
1 The magnitude of the pulse
2 Effects and mitigation
3 Dynamic Equations
4 Possible causes
5 Software
6 Mitigating measures
7 Applications
8 See also
9 References
10 External links

[edit] The magnitude of the pulse
Water hammer can be analyzed by two different approaches, rigid column theory which ignores compressibility of the fluid and elasticity of the walls of the pipe, or by a full analysis including elasticity. When the time it takes a valve to close is long compared to the propagation time for a pressure wave to travel the length of the pipe, then rigid column theory is appropriate; otherwise considering elasticity may be necessary[1]. Below are two approximations for the peak pressure, one that considers elasticity, but assumes the valve closes instantaneously, and a second that neglects elasticity but includes a finite time for the valve to close.

The maximum magnitude of the water hammer pulse, assuming a valve that closes instaneously, can be estimated from the Joukowsky equation [2]

?P = ?a?C

where ?P is the magnitude of the pressure wave (Pa), ? is the density of the fluid (kgm-3), a is the speed of sound in the fluid (ms-1), and ?C is the change in the fluid's velocity (ms-1). The pulse comes about due to Newton's laws of motion and the continuity equation applied to the deceleration of a fluid element [3].

As the speed of sound in a fluid is the , the peak pressure will depend on the fluid compressibility if the valve is closed abruptly.

When the valve is closed slowly compared to the transit time for a pressure wave to travel the length of the pipe, the elasticity can be neglected, and the phenomenon can be described in terms of intertance or rigid column theory. For this case, one approximation to the maximum pressure (using Imperial units), P, produced in a water filled line is:

P = 0.07VL / t + P1

where P1 is the inlet pressure, V is the flow velocity in ft/sec, t is the valve closing time in seconds and L is the upstream pipe length in feet [4]

To keep water hammer low, pipe-sizing charts for some applications recommend flow velocity at or below 5 ft/s (1.5 m/s).

[edit] Effects and mitigation
If the pipe is suddenly closed at the outlet (downstream), the mass of water before the closure is still moving forward with some velocity, building up a high pressure and shock waves. In domestic plumbing this is experienced as a loud bang resembling a hammering noise. Water hammer can cause pipelines to break if the pressure is high enough. Air traps or stand pipes (open at the top) are sometimes added as dampers to water systems to provide a cushion to absorb the force of moving water in order to prevent damage to the system. (At some hydroelectric generating stations what appears to be a water tower is actually one of these devices.)

On the other hand, when a valve in a pipe is closed, the water downstream of the valve will attempt to continue flowing, creating a vacuum that may cause the pipe to collapse or implode. This problem can be particularly acute if the pipe is on a downhill slope. To prevent this, air and vacuum relief valves, or air vents, are installed just downstream of the valve to allow air to enter the line and prevent this vacuum from occurring[citation needed].

In the home water hammer often occurs when a dishwasher, washing machine, or toilet shuts off water flow, resulting in a loud bang or banging sound. A hydropneumatic device similar in principle to a shock absorber called a 'Water Hammer Arrestor' can be installed between the water pipe and the machine which will absorb the shock and stop the banging.

Expansion joints on a steam line that have been destroyed by steam hammerSteam distribution systems may also be vulnerable to a situation similar to water hammer, known as steam hammer. In a steam system, water hammer most often occurs when some of the steam condenses into water in a horizontal section of the steam piping. Subsequently, steam picks up the water, forms a "slug" and hurls it at high velocity into a pipe fitting, creating a loud hammering noise and greatly stressing the pipe. This condition is usually caused by a poor condensate drainage strategy.

Where air filled traps are used, these eventually become depleted of their trapped air over a long period of time through absorption into the water. This can be cured by shutting off the supply and draining the system by opening taps at the highest and lowest locations, which restores the air to the traps and then closing the taps and opening the supply.

Hydroelectric power plants must be carefully designed and maintained because the water hammer can cause water pipes to fail catastrophically. One of the first to successfully investigate the water hammer problem was the Italian engineer Lorenzo Allievi.

[edit] Dynamic Equations
The water hammer effect can be simulated by solving the following partial differential equations.

where V is the fluid velocity inside pipe, ? is the fluid density and Bm is the equivalent bulk modulus, f is the friction factor.

[edit] Possible causes
Sudden valve closure
Pump failure
Check valve slam (due to sudden deceleration, a check valve may slam shut rapidly, depending on the dynamic characteristic of the check valve and the mass of the water between a check valve and tank).

[edit] Software
Most water hammer software packages use the method of characteristics [3] to solve the differential equations involved. This method works well if the wave speed does not vary in time due to either air or gas entrainment in a pipeline. Many commercial and non commercial packages exist today.

Software packages vary in complexity, dependent on the processes modeled. The more sophisticated packages may have any of the following features:

Multiphase flow capabilities
An algorithm for cavitation growth and collapse
Unsteady friction - the pressure waves will dampen as turbulence is generated and due to variations in the flow velocity distribution
Varying bulk modulus for higher pressures (water will become less compressible)
Fluid structure interaction - the pipeline will react on the varying pressures and will cause pressure waves itself

[edit] Mitigating measures
Water hammer has caused accidents and fatalities, but is usually less threatening. In many cases damage is limited to breakage of pipes or appendages. An engineer should always assess (at least qualitatively) risk of a pipeline burst. Pipelines with hazardous goods should always receive special attention and should be thoroughly investigated.

The following characteristics may reduce or eliminate water hammer:

Low fluid velocities.
Slowly closing valves. Toilet flush valves are available in a quiet flush type that closes quietly.
High pipeline pressure rating (expensive).
Good pipeline control (start-up and shut-down procedures).
Water towers (used in many drinking water systems) help maintain steady flow rates and trap large pressure fluctuations.
Air vessels work in much the same way as water towers, but are pressurized. They typically have an air cushion above the fluid level in the vessel, which may be regulated or separated by a bladder. Sizes of air vessels may be up to hundreds of cubic meters on large pipelines. They come in many shapes, sizes and configurations. Such vessels often are called accumulators.
Air valves are often used to remediate low pressures at high points in the pipeline. Though effective, sometimes large numbers of air valves need be installed. These valves also allow air into the system, which is often unwanted.
Shorter branch pipe lengths.
Shorter lengths of straight pipe, i.e. add elbows, expansion loops. Water hammer is related to the speed of sound in the fluid, and elbows reduce the influences of pressure waves.
Arranging the larger piping in loops that supply shorter smaller run-out pipe branches. With looped piping, lower velocity flows from both sides of a loop can serve a branch.
UPS (uninterruptible power supply) is sometimes installed to dampen the initial pressure wave by keeping the system running for some time after a power trip.[citation needed]
Flywheel on pump.
Pumping station bypass.

[edit] Applications
The water hammer principle can be used to create a simple water pump called a hydraulic ram.
Leaks can sometimes be detected using water hammer.
Enclosed air pockets can be detected in pipelines.
A fluid is defined as a substance that continually deforms (flows) under an applied shear stress. All liquids and all gases are fluids. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids.

In common usage, "fluid" is often used as a synonym for "liquid", with no implication that gas could also be present. For example, "brake fluid" is hydraulic oil and will not perform its required function if there is gas in it. This colloquial usage of the term is also common in medicine ("take plenty of fluids"), and in nutrition.

Liquids form a free surface (that is, a surface not created by the container) while gases do not. The distinction between solids and fluid is not entirely obvious. The distinction is made by evaluating the viscosity of the substance. Silly Putty can be considered to behave like a solid or a fluid, depending on the time period over which it is observed. It is best described as a viscoelastic fluid.

Fluids display such properties as:

not resisting deformation, or resisting it only lightly (viscosity), and
the ability to flow (also described as the ability to take on the shape of the container).
These properties are typically a function of their inability to support a shear stress in static equilibrium.

Solids can be subjected to shear stresses, and to normal stresses - both compressive and tensile. In contrast, ideal fluids can only be subjected to normal, compressive stress which is called pressure. Real fluids display viscosity and so are capable of being subjected to low levels of shear stress.

In a solid, shear stress is a function of strain, but in a fluid, shear stress is a function of rate of strain. A consequence of this behavior is Pascal's law which describes the role of pressure in characterizing a fluid's state.

Depending on the relationship between shear stress, and the rate of strain and its derivatives, fluids can be characterized as:

Newtonian fluids : where stress is directly proportional to rate of strain, and
Non-Newtonian fluids : where stress is proportional to rate of strain, its higher powers and derivatives.
The behavior of fluids can be described by the Navier-Stokes equations—a set of partial differential equations which are based on:

continuity (conservation of mass),
conservation of linear momentum
conservation of angular momentum
conservation of energy.
The study of fluids is fluid mechanics, which is subdivided into fluid dynamics and fluid statics depending on whether the fluid is in motion.

(Paramore song). For Under Pressure, see Under Pressure (disambiguation).
Pressure (symbol: p or sometimes P) is the force per unit area applied to an object in a direction perpendicular to the surface. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.

Contents [hide]
1 Definition
1.1 Formula
1.2 Units
1.3 Examples
1.4 Scalar nature
2 Types
2.1 Explosion or deflagration pressures
2.2 Negative pressures
2.3 Stagnation pressure
2.4 Surface pressure
2.5 Pressure of an ideal gas
3 See also
4 Notes
5 External links

[edit] Definition
Pressure is an effect which occurs when a force is applied on a surface. The symbol of pressure is p (lower case). The upper case P is normally reserved for power.

[edit] Formula
Conjugate variables
of thermodynamics
Pressure Volume
(Stress) (Strain)
Temperature Entropy
Chem. potential Particle no.
Mathematically:

where:

p is the pressure,
F is the normal force,
A is the area.
Pressure is a scalar quantity, and has SI units of pascals; 1 Pa = 1 N/m2, and has EES units of psi; 1 psi = 1 lb/in2.

Pressure is transmitted to solid boundaries or across arbitrary sections of fluid normal to these boundaries or sections at every point. It is a fundamental parameter in thermodynamics and it is conjugate to volume.

[edit] Units

Mercury columnThe SI unit for pressure is the pascal (Pa), equal to one newton per square metre (N·m-2 or kg·m-1·s-2). This special name for the unit was added in 1971; before that, pressure in SI was expressed simply as N/m2.

Non-SI measures such as pound per square inch (psi) and bar are used in parts of the world. The cgs unit of pressure is the barye (ba), equal to 1 dyn·cm-2. Pressure is sometimes expressed in grams-force/cm2, or as kg/cm2 and the like without properly identifying the force units. But using the names kilogram, gram, kilogram-force, or gram-force (or their symbols) as units of force is expressly forbidden in SI. The technical atmosphere (symbol: at) is 1 kgf/cm2. In US Customary units, it is 14.696 psi.

Some meteorologists prefer the hectopascal (hPa) for atmospheric air pressure, which is equivalent to the older unit millibar (mbar). Similar pressures are given in kilopascals (kPa) in most other fields, where the hecto prefix is rarely used. The unit inch of mercury (inHg, see below) is still used in the United States. Oceanographers usually measure underwater pressure in decibars (dbar) because an increase in pressure of 1 dbar is approximately equal to an increase in depth of 1 meter. Scuba divers often use a manometric rule of thumb: the pressure exerted by ten metres depth of water is approximately equal to one atmosphere.

The standard atmosphere (atm) is an established constant. It is approximately equal to typical air pressure at earth mean sea level and is defined as follows:

standard atmosphere = 101325 Pa = 101.325 kPa = 1013.25 hPa.
Because pressure is commonly measured by its ability to displace a column of liquid in a manometer, pressures are often expressed as a depth of a particular fluid (e.g., inches of water). The most common choices are mercury (Hg) and water; water is nontoxic and readily available, while mercury's high density allows for a shorter column (and so a smaller manometer) to measure a given pressure. The pressure exerted by a column of liquid of height h and density ? is given by the hydrostatic pressure equation p = ?gh. Fluid density and local gravity can vary from one reading to another depending on local factors, so the height of a fluid column does not define pressure precisely. When millimeters of mercury or inches of mercury are quoted today, these units are not based on a physical column of mercury; rather, they have been given precise definitions that can be expressed in terms of SI units. The water-based units still depend on the density of water, a measured, rather than defined, quantity. These manometric units are still encountered in many fields. Blood pressure is measured in millimeters of mercury in most of the world, and lung pressures in centimeters of water are still common.

Gauge pressure is often given in units with 'g' appended, eg 'kPag' or 'psig', and units for measurements of absolute pressure are sometimes given a suffix of 'a', to avoid confusion, for example 'kPaa', 'psia'.

Presently or formerly popular pressure units include the following:

atmosphere (atm)
manometric units:
centimeter, inch, and millimeter of mercury (torr)
millimeter, centimeter, meter, inch, and foot of water
customary units:
kip, ton-force (short), ton-force (long), pound-force, ounce-force, and poundal per square inch
pound-force, ton-force (short), and ton-force (long)
non-SI metric units:
bar, decibar, millibar
kilogram-force, or kilopond, per square centimetre (technical atmosphere)
gram-force and tonne-force (metric ton-force) per square centimetre
barye (dyne per square centimetre)
kilogram-force and tonne-force per square metre
sthene per square metre (pieze)
Pressure Units
pascal
(Pa)
bar
(bar) technical atmosphere
(at)
atmosphere
(atm)
torr
(Torr) pound-force per
square inch
(psi)
1 Pa = 1 N/m2 10-5 1.0197×10-5 9.8692×10-6 7.5006×10-3 145.04×10-6
1 bar 100,000 = 106 dyn/cm2 1.0197 0.98692 750.06 14.5037744
1 at 98,066.5 0.980665 = 1 kgf/cm2 0.96784 735.56 14.223
1 atm 101,325 1.01325 1.0332 = 1 atm 760 14.696
1 torr 133.322 1.3332×10-3 1.3595×10-3 1.3158×10-3 = 1 Torr; ˜ 1 mmHg 19.337×10-3
1 psi 6,894.76 68.948×10-3 70.307×10-3 68.046×10-3 51.715 = 1 lbf/in2

Example reading: 1 Pa = 1 N/m2 = 10-5 bar = 10.197×10-6 at = 9.8692×10-6 atm, etc.

[edit] Examples
As an example of varying pressures, a finger can be pressed against a wall without making any lasting impression; however, the same finger pushing a thumbtack can easily damage the wall. Although the force applied to the surface is the same, the thumbtack applies more pressure because the point concentrates that force into a smaller area. Pressure is transmitted to solid boundaries or across arbitrary sections of fluid normal to these boundaries or sections at every point. Unlike stress, pressure is defined as a scalar quantity.

Another example is of a common knife. If we try and cut a fruit with the flat side it obviously won't cut. But if we take the thin side, it will cut smoothly. The reason is, the flat side has a greater surface area(less pressure) and so it does not cut the fruit. When we take the thin side, the surface area is reduced and so it cuts the fruit easily and quickly. This is one example of a practical application of Pressure.

The gradient of pressure is called the force density. For gases, pressure is sometimes measured not as an absolute pressure, but relative to atmospheric pressure; such measurements are called gauge pressure (also sometimes spelled gage pressure).[1] An example of this is the air pressure in an automobile tire, which might be said to be "220 kPa/32psi", but is actually 220 kPa/32 psi above atmospheric pressure. Since atmospheric pressure at sea level is about 100 kPa/14.7 psi, the absolute pressure in the tire is therefore about 320 kPa/46.7 psi. In technical work, this is written "a gauge pressure of 220 kPa/32 psi". Where space is limited, such as on pressure gauges, name plates, graph labels, and table headings, the use of a modifier in parentheses, such as "kPa (gauge)" or "kPa (absolute)", is permitted. In non-SI technical work, a gauge pressure of 32 psi is sometimes written as "32 psig" and an absolute pressure as "32 psia", though the other methods explained above that avoid attaching characters to the unit of pressure are preferred.[2]

Gauge pressure is the relevant measure of pressure wherever one is interested in the stress on storage vessels and the plumbing components of fluidics systems. However, whenever equation-of-state properties, such as densities or changes in densities, must be calculated, pressures must be expressed in terms of their absolute values. For instance, if the atmospheric pressure is 100 kPa, a gas (such as helium) at 200 kPa (gauge) (300 kPa [absolute]) is 50 % denser than the same gas at 100 kPa (gauge) (200 kPa [absolute]). Focusing on gauge values, one might erroneously conclude the first sample had twice the density of the second one.

[edit] Scalar nature
In a static gas, the gas as a whole does not appear to move. The individual molecules of the gas, however, are in constant random motion. Because we are dealing with an extremely large number of molecules and because the motion of the individual molecules is random in every direction, we do not detect any motion. If we enclose the gas within a container, we detect a pressure in the gas from the molecules colliding with the walls of our container. We can put the walls of our container anywhere inside the gas, and the force per unit area (the pressure) is the same. We can shrink the size of our "container" down to an infinitely small point, and the pressure has a single value at that point. Therefore, pressure is a scalar quantity, not a vector quantity. It has magnitude but no direction sense associated with it. Pressure acts in all directions at a point inside a gas. At the surface of a gas, the pressure force acts perpendicular (at right angle) to the surface.

A closely related quantity is the stress tensor s, which relates the vector force F to the vector area A via

This tensor may be divided up into a scalar part (pressure) and a traceless tensor part shear. The shear tensor gives the force in directions parallel to the surface, usually due to viscous or frictional forces. The stress tensor is sometimes called the pressure tensor, but in the following, the term "pressure" will refer only to the scalar pressure.

[edit] Types

[edit] Explosion or deflagration pressures
Explosion or deflagration pressures are the result of the ignition of explosive gases, mists, dust/air suspensions, in unconfined and confined spaces.

[edit] Negative pressures
While pressures are generally positive, there are several situations in which negative pressures may be encountered:

When dealing in relative (gauge) pressures. For instance, an absolute pressure of 80 kPa may be described as a gauge pressure of -21 kPa (i.e., 21 kPa below an atmospheric pressure of 101 kPa).
When attractive forces (e.g., Van der Waals forces) between the particles of a fluid exceed repulsive forces. Such scenarios are generally unstable since the particles will move closer together until repulsive forces balance attractive forces. Negative pressure exists in the transpiration pull of plants.
The Casimir effect can create a small attractive force due to interactions with vacuum energy; this force is sometimes termed 'vacuum pressure' (not to be confused with the negative gauge pressure of a vacuum).
Depending on how the orientation of a surface is chosen, the same distribution of forces may be described either as a positive pressure along one surface normal, or as a negative pressure acting along the opposite surface normal.
In the cosmological constant.

[edit] Stagnation pressure
Stagnation pressure is the pressure a fluid exerts when it is forced to stop moving. Consequently, although a fluid moving at higher speed will have a lower static pressure, it may have a higher stagnation pressure when forced to a standstill. Static pressure and stagnation pressure are related by the Mach number of the fluid. In addition, there can be differences in pressure due to differences in the elevation (height) of the fluid. See Bernoulli's equation (note: Bernoulli's equation only applies for incompressible flow).

The pressure of a moving fluid can be measured using a Pitot tube, or one of its variations such as a Kiel probe or Cobra probe, connected to a manometer. Depending on where the inlet holes are located on the probe, it can measure static pressure or stagnation pressure.

[edit] Surface pressure
There is a two-dimensional analog of pressure – the lateral force per unit length applied on a line perpendicular to the force.

Surface pressure is denoted by p and shares many similar properties with three-dimensional pressure. Properties of surface chemicals can be investigated by measuring pressure/area isotherms, as the two-dimensional analog of Boyle's law, pA = k, at constant temperature.

[edit] Pressure of an ideal gas
In an ideal gas, molecules have no volume and do not interact. Pressure varies linearly with temperature, volume, and quantity according to the ideal gas law,

where:

p is the absolute pressure of the gas
n is the amount of substance (in mole)
T is the temperature (in kelvin)
V is the volume
R is the ideal gas constant.

Real gases exhibit a more complex dependence on the variables of state.[3]

[edit] See also
Atmospheric pressure
Blood pressure
Boyle's Law
Combined gas law
Conversion of units
Dynamic pressure
Ideal gas law
Kinetic theory
Microphone
Orders of magnitude (pressure)
Partial pressure
Pressure measurement
Sound pressure
Timeline of temperature and pressure measurement technology
Units conversion by factor-label
Vacuum
Vacuum pump
Vapor pressure

[edit] Notes
^ The preferred spelling varies by country and even by industry. Further, both spellings are often used within a particular industry or country. Industries in British English-speaking countries typically use the "gauge" spelling. Many of the largest American manufacturers of pressure transducers and instrumentation use the spelling "gage pressure" in their most formal documentation (Honeywell-Sensotec’s FAQ page and Fluke Corporation’s product search page).
^ NIST, Rules and Style Conventions for Expressing Values of Quantities, Sect. 7.4.
^ P. Atkins, J. de Paula “Elements of Physical Chemistry” 4TH Ed, W.H. Freeman, 2006. ISBN 0-7167-7329-5.

[edit] External links
Pressure calculator
A free and downloadable Java pressure simulation applet
Thermodynamics - A chapter from an online textbook
Introduction to Fluid Statics and Dynamics on Project PHYSNET
An exercise in air pressure
Pressure being a scalar quantity
Online pressure converter for 52 different pressure units
Retrieved from "http://en.wikipedia.org/wiki/Pressure"

The US Navy is conducting field trials for mine clearing using water hammer.

[edit] See also
Blood hammer
Cavitation
Fluid dynamics
Water hammer pulse
Flow control valve
From Wikipedia, the free encyclopedia
Jump to: navigation, search
A flow control valve regulates the flow or pressure of a fluid. Control valves normally respond to signals generated by independent devices such as flow meters or temperature gauges.

Globe control valve with the pneumatic actuator and smart positionerControl valves are normally fitted with actuators and positioners. Pneumatically-actuated globe valves are widely used for control purposes in many industries, although quarter-turn types such as (modified) ball and butterfly valves are also used.

Control valves can also work with hydraulic actuators (also known as hydraulic pilots). These types of valves are also known as Automatic Control Valves. The hydraulic actuators will respond to changes of pressure or flow and will open/close the valve. Automatic Control Valves do not require an external power source, meaning that the fluid pressure is enough to open and close the valve. Automatic control valves include: pressure reducing valves, flow control valves, back-pressure sustaining valves, altitude valves, and relief valves. An altitude valve controls the level of a tank. The altitude valve will remain open while the tank is not full and it will close when the tanks reaches its maximum level. The opening and closing of the valve requires no external power source (electric, pneumatic, or man power), it is done automatically, hence its name.

[edit] Control valve cavitation
Cavitation damage is characterised by a rough cinder like appearance of the eroded surface.[1] Cavitation can be treated by several means. The first is to eliminate the cavitation by managing the pressure drop. Specialist control valve trims can be used for this purpose. A second method is to minimse the damage by isolating the cavitation away from valve surfaces and by hardening the surfaces it does impact, the third way is to modify the process.

[edit] References
^ Control Valve Handbook, 4th edition, Fisher Controls International, 2005, pp. 138, http://www.documentation.emersonprocess.com/groups/public/documents/book/cvh99.pdf
Flow measurement
From Wikipedia, the free encyclopedia
(Redirected from Flow meter)
Jump to: navigation, search
Flow measurement is the quantification of bulk fluid movement. It can be measured in a variety of ways.

Contents [hide]
1 Units of measurement
1.1 Gas
1.2 Liquid
2 Mechanical flow meters
2.1 Bucket-and-stopwatch
2.2 Piston meter
2.3 Woltmann meter
2.4 Multi-jet meter
2.5 Venturi meter
2.5.1 Dall tube
2.6 Orifice plate
2.7 Pitot tube
2.8 Multi-hole pressure probe
2.9 Paddle wheel
2.10 Pelton wheel
2.11 Oval gear meter
3 Optical flow meters
4 Turbine flow meter
5 Open channel flow measurement
5.1 Level to flow
5.2 Area / velocity
5.3 Dye testing
6 Thermal mass flow meters
7 Vortex flowmeters
8 Electromagnetic, ultrasonic and coriolis flow meters
8.1 Magnetic flow meters
8.2 Ultrasonic (Doppler, transit time) flow meters
8.3 Coriolis flow meters
9 Laser Doppler flow measurement
10 See also
11 External links

[edit] Units of measurement
Both gas and liquid flow can be measured in volumetric or mass flow rates (such as litres per second or kg/s). These measurements can be converted between one another if the materials density is known. The density for a liquid is almost independent of the liquids conditions, however this is not the case for a gas, whose density highly depends upon pressure, temperature and to a lesser extent, the gas composition.

When gases or liquids are transferred for their energy content (such as the sale of Natural Gas) the flow rate my also be expressed in terms of energy flow, such as GJ/hour or BTU/day. The energy flow rate is the volume flow rate multiplied by the energy content per unit volume or mass flow rate multiplied by the energy content per unit mass. Where accurate energy flow rate is desired, most flow meters will be used to calculate the volume or mass flow rate which is then adjusted to the energy flow rate by the use of a flow computer.

In engineering contexts, the volumetric flow rate is usually given the symbol Q and the mass flow rate the symbol .

[edit] Gas
Gases are compressible and change volume when placed under pressure or are heated or cooled. A volume of gas under one set of conditions (pressure and temperature) is not equivalent to the same gas under different conditions. References will be made to "actual" flow rate through a meter and "standard" or "base" flow rate through a meter with units such as acm/h, (actual cubic meters per hour) Kscm/h (Kilo standard cubic meters per hour) or MSCFD (thousands of standard cubic feet per day) . The actual flow rate is the volume flow per time that the meter measured at the pressure and temperature conditions in the meter. The standard flow rate is the volume flow per time that the measured gas would take up if it was under a standard set of conditions. Converting back to a standard allows two measured samples to be compared, even if they were measured under different conditions. The conversion between different pressure conditions is via variations to the Ideal Gas Law and are usually performed by a flow computer.

The change in volume is only a physical change, so the mass of the gas does not change. Meters that measure mass flow do not need a conversion to compare two samples.

Gas mass flow rate can be directly measured, independent of pressure and temperature effects with Thermal Mass Flow Meter; Coriolis mass flow meter; Mass Flow Controller technology.

[edit] Liquid
For liquids, other units are used depending upon the application and industry but might include gallons (U.S. liquid or imperial) per minute, liters per second, bushels per minute and, when describing river flows, cumecs (cubic metres per second) or acre-feet per day.

[edit] Mechanical flow meters
There are several types of mechanical flow meter

[edit] Bucket-and-stopwatch
Perhaps the simplest way to measure volumetric flow is to measure how long it takes to fill a container. A simple example would be using a bucket of known volume, filled by a hose. The stopwatch is started when the flow starts, and stopped when the bucket overflows. The volume divided by the time gives the flow. The bucket-and-stopwatch method is an off-line method.

[edit] Piston meter
Because they are used for domestic water measurement, piston meters, also known as rotary piston or semi-positive displacement meters, are the most common flow measurement devices in the UK and are used for almost all meter sizes up to and including 40 mm (1 1/2"). The piston meter operates on the principle of a piston rotating within a chamber of known volume. For each rotation, an amount of water passes through the piston chamber. Through a gear mechanism and, sometimes, a magnetic drive, a needle dial and odometer type display is advanced.

[edit] Woltmann meter
Woltman meters, commonly referred to as Helix meters are popular at larger sizes. Jet meters (single or Multi-Jet) are increasing in popularity in the UK at larger sizes and are common place in the EU.

[edit] Multi-jet meter
A multi-jet meter is a velocity type meter which has an impeller which rotates horizontally on a vertical shaft. The impeller element is in a housing in which multiple inlet ports direct the fluid flow at the impeller causing it to rotate in a specific direction in proportion to the flow velocity. This meter works mechanically much like a paddle wheel meter except that the ports direct the flow at the impeller equally from several points around the circumference of the element, where a paddle wheel normally only receives flow from one offset flow stream.

[edit] Venturi meter
Another method of measurement, known as a venturi meter, is to constrict the flow in some fashion, and measure the differential pressure (using a pressure sensor) that results across the constriction. This method is widely used to measure flow rate in the transmission of gas through pipelines, and has been used since Roman Empire times.

[edit] Dall tube
The Dall tube is a shortened version of a Venturi meter with a lower pressure drop than an orifice plate. Both flow meters the flow rate of Dall tube is determined by measuring the pressure drop caused by restriction in the conduit. The pressure differential is measured using diaphragm pressure transducers with digital read out. Since these meters have significantly lower permanent pressure losses than the orifice meters, the Dall tubes have widely been used for measuring the flow rate of large pipeworks.

[edit] Orifice plate
Another simple method of measurement uses an orifice plate, which is basically a plate with a hole through it. It is placed in the flow and constricts the flow. It uses the same principle as the venturi meter in that the differential pressure relates to the velocity of the fluid flow (Bernoulli's principle).

The use of orifice plates for the measurement of flow of natural gas is covered by American Gas Association Report Number 3.

[edit] Pitot tube
A Pitot tube is a pressure measuring instrument used to measure fluid flow velocity by determining the stagnation pressure. Bernoulli's equation is used to calculate the dynamic pressure and hence fluid velocity.

[edit] Multi-hole pressure probe
Multi-hole pressure probes (also called impact probes) extend the theory of pitot tube to more than one dimension. A typical impact probe consists of three or more holes (depending on the type of probe) on the measuring tip arranged in a specific pattern. More holes allow the instrument to measure the direction of the flow velocity in addition to its magnitude (after appropriate calibration). Three-holes arranged in a line allow the pressure probes to measure the velocity vector in two dimensions. Introduction of more holes e.g., five holes arranged in a 'plus' formation allow measurement of the three-dimensional velocity vector.

[edit] Paddle wheel
The paddle wheel translates the mechanical action of paddles rotating in the liquid flow around an axle into a user-readable rate of flow (gallon per minute, litre per minute, etc.). The paddle tends to be inserted into the flow.

[edit] Pelton wheel
The Pelton wheel turbine (better described as a radial turbine) translates the mechanical action of the Pelton wheel rotating in the liquid flow around an axis into a user-readable rate of flow (gpm, lpm, etc.). The Pelton wheel tends to have all the flow traveling around it with the inlet flow focused on the blades by a jet. The original Pelton wheels were used for the generation of power and consisted of a radial flow turbine with "reaction cups" which not only move with the force of the water on the face but return the flow in opposite direction using this change of fluid direction to further increase the efficiency of the turbine.

[edit] Oval gear meter
An oval gear meter is a positive displacement meter that uses two or more oblong gears configured to rotate at right angles to one another, forming a tee shape. Such a meter has two sides, which can be called A and B. No fluid passes through the center of the meter, where the teeth of the two gears always mesh. On one side of the meter (A), the teeth of the gears close off the fluid flow because the elongated gear on side A is protruding into the measurement chamber, while on the other side of the meter (B), a cavity holds a fixed volume of fluid in a measurement chamber. As the fluid pushes the gears, it rotates them, allowing the fluid in the measurement chamber on side B to be released into the outlet port. Meanwhile, fluid entering the inlet port will be driven into the measurement chamber of side A, which is now open. The teeth on side B will now close off the fluid from entering side B. This cycle continues as the gears rotate and fluid is metered through alternating measurement chambers. Permanent magnets in the rotating gears can transmit a signal to an electric reed switch or current transducer for flow measurement.

[edit] Optical flow meters
Optical flow meters use light to determine flow rate. Small particles which accompany natural and industrial gases pass through two laser beams focused in a pipe by illuminating optics. Laser light is scattered when a particle crosses the first beam. The detecting optics collects scattered light on a photodetector, which then generates a pulse signal. If the same particle crosses the second beam, the detecting optics collect scattered light on a second photodetector, which converts the incoming light into a second electrical pulse. By measuring the time interval between these pulses, the gas velocity is calculated as V=D/T where D is the distance between the laser beams and T is the time interval.

Laser-based optical flow meters measure the actual speed of particles, a property which is not dependent on thermal conductivity of gases, variations in gas flow or composition of gases. The different operating principle enables optical laser technology to deliver highly accurate flow data, even in challenging environments which may include high temperature, low flow rates, high pressure, high humidity, pipe vibration and acoustic noise.

Optical flow meters are very stable with no moving parts and deliver a highly repeatable measurement over the life of the product. Because distance between the two laser sheets does not change, optical flow meters do not require periodic calibration after its initial commissioning. Optical flow meters require only one installation point, instead of the two installation points typically required by other types of meters. A single installation point is simpler, requires less maintenance and is less prone to errors.

Optical flow meters are capable of measuring flow from 0.1 m/s to faster than 100 m/s (1000:1 turn down ratio) and have been demonstrated to be effective for the measurement of flare gases, a major global contributor to the emissions associated with climate change.[1]...

[edit] Turbine flow meter
The turbine flow meter (better described as an axial turbine) translates the mechanical action of the turbine rotating in the liquid flow around an axis into a user-readable rate of flow (gpm, lpm, etc.). The turbine tends to have all the flow traveling around it.

The turbine wheel is set in the path of a fluid stream. The flowing fluid impinges on the turbine blades, imparting a force to the blade surface and setting the rotor in motion. when a steady rotation speed has been reached, the speed is proportional to fluid velocity.

The use of turbine flow meters for the measurement of natural gas flow is covered by the American Gas Association Report Number 7.

[edit] Open channel flow measurement

[edit] Level to flow
The level of the water is measured at a designated point behind a hydraulic structure (a weir or flume) using various means (bubblers, ultrasonic, float, and differential pressure are common methods). This depth is converted to a flow rate according to a theoretical formula of the form Q=KHX where Q is the flow rate, K is a constant, H is the water level and X is an exponent which varies with the device used, or it is converted according to empirically derived level/flow data points (a 'flow curve'). The flow rate can then integrated over time into volumetric flow.

[edit] Area / velocity
The cross-sectional area of the flow is calculated from a depth measurement and the average velocity of the flow is measured directly (Doppler and propeller methods are common). Velocity times the cross-sectional area yields a flow rate which can be integrated into volumetric flow.

[edit] Dye testing
A known amount of dye (or salt) per unit time is added to a flow stream. After complete mixing, the concentration is measured. The dilution rate equals the flow rate.

[edit] Thermal mass flow meters
Thermal mass flow meters generally use combinations of heated elements and temperature sensors to measure the difference between static and flowing heat transfer to a fluid and infer its flow with a knowledge of the fluid's specific heat and density. The fluid temperature is also measured and compensated for. If the density and specific heat characteristics of the fluid are constant, the meter can provide a direct mass flow readout, and does not need any additional pressure temperature compensation over their specified range.

Technological progress allows today to manufacture thermal mass flow meters on a microscopic scale as MEMS sensors, these flow devices can be used to measure flow rates in the range of nano litres or micro litres per minute.

Thermal mass flow meter technology is used for compressed air, nitrogen, helium, argon, oxygen, natural gas. In fact, most gases can be measured as long as they are fairly clean and non-corrosive.

Temperature at the sensors varies depending upon the mass flow

[edit] Vortex flowmeters
Another method of flow measurement involves placing a bluff body (called a shedder bar) in the path of the fluid. As the fluid passes this bar, disturbances in the flow called vortices are created. The vortices trail behind the cylinder, alternatively from each side of the bluff body. This vortex trail is called the Von Kármán vortex street after von Karman's 1912 mathematical description of the phenomenon. The frequency at which these vortices alternate sides is essentially proportional to the flow rate of the fluid. Inside, atop, or downstream of the shedder bar is a sensor for measuring the frequency of the vortex shedding. This sensor is often a piezoelectric crystal, which produces a small, but measurable, voltage pulse every time a vortex is created. Since the frequency of such a voltage pulse is also proportional to the fluid velocity, a volumetric flow rate is calculated using the cross sectional area of the flow meter. The frequency is measured and the flow rate is calculated by the flowmeter electronics.

With f= SV/L where,

f = the frequency of the vortices
L = the characteristic length of the bluff body
V = the velocity of the flow over the bluff body
S = Strouhal number, which is essentially a constant for a given body shape within its operating limits

[edit] Electromagnetic, ultrasonic and coriolis flow meters
Modern innovations in the measurement of flow rate incorporate electronic devices that can correct for varying pressure and temperature (i.e. density) conditions, non-linearities, and for the characteristics of the fluid.

[edit] Magnetic flow meters

Industrial magnetic flowmeterThe most common flow meter apart from the mechanical flow meters, is the magnetic flow meter, commonly referred to as a "mag meter" or an "electromag". A magnetic field is applied to the metering tube, which results in a potential difference proportional to the flow velocity perpendicular to the flux lines. The physical principle at work is Faraday's law of electromagnetic induction. The magnetic flow meter requires a conducting fluid, e.g. water, and an electrical insulating pipe surface, e.g. a rubber lined non magnetic steel tube.

[edit] Ultrasonic (Doppler, transit time) flow meters
Ultrasonic flow meters measure the difference of the transit time of ultrasonic pulses propagating in and against flow direction. This time difference is a measure for the average velocity of the fluid along the path of the ultrasonic beam. By using the absolute transit times both the averaged fluid velocity and the speed of sound can be calculated. Using the two transit times tup and tdown and the distance between receiving and transmitting transducers L and the inclination angle a one can write the equations:

and

where v is the average velocity of the fluid along the sound path and c is the speed of sound.

The use of Ultrasonic flow meters for the measurement of natural gas flow is covered by the American Gas Association Report Number 9. There are also calculations in the American Gas Association Report Number 10 to determine the expected speed of sound for a given sample of gas. This can be compared to the speed of sound empirically measured by an Ultrasonic flow meter and for the purposes of monitoring the quality of the flow meters measurements. A drop in quality is in indication that the meter needs servicing.

Schematic view of a flow sensor.Measurement of the Doppler shift resulting in reflecting an ultrasonic beam off the flowing fluid is another recent innovation made possible by electronics. By passing an ultrasonic beam through the tissues, bouncing it off of a reflective plate then reversing the direction of the beam and repeating the measurement the volume of blood flow can be estimated. The speed of transmission is affected by the movement of blood in the vessel and by comparing the time taken to complete the cycle upstream versus downstream the flow of blood through the vessel can be measured. The difference between the two speeds is a measure of true volume flow. A wide-beam sensor can also be used to measure flow independent of the cross-sectional area of the blood vessel.

For the Doppler principle to work in a flowmeter it is mandatory that the flow stream contains sonically reflective materials, such as solid particles or entrained air bubbles.

[edit] Coriolis flow meters
Using the Coriolis effect that causes a laterally vibrating tube to distort, a direct measurement of mass flow can be obtained in a coriolis flow meter. Furthermore a direct measure of the density of the fluid is obtained. Coriolis measurement can be very accurate irrespective of the type of gas or liquid that is measured; the same measurement tube can be used for hydrogen gas and bitumen without recalibration.

The use of Coriolis flow meters for the measurement of natural gas flow is covered by the American Gas Association Report Number 11.

[edit] Laser Doppler flow measurement

Laser-doppler flow meter.Blood flow can be measured through the use of a monochromatic laser diode. The laser probe is inserted into a tissue and turned on, where the light scatters and a small portion is reflected back to the probe. The signal is then processed to calculate flow within the tissues. There are limitations to the use of a laser Doppler probe; flow within a tissue is dependent on volume illuminated, which is often assumed rather than measured and varies with the optical properties of the tissue. In addition, variations in the type and placement of the probe within identical tissues and individuals result in variations in reading. The laser Doppler has the advantage of sampling a small volume of tissue, allowing for great precision, but does not necessarily represent the flow within an entire organ. The flow meter is much more useful for relative rather than absolute measurements.

[edit] See also
Mass flow rate
Volumetric flow rate
Gas meter
Water Meter
Orifice plate
Automatic Meter Reading
Airspeed indicator
Air flow meter
mass flow meter
Laser Doppler velocimetry
Ford viscosity cup

[edit] External links
A pneumatic actuator converts energy (in the form of compressed air, typically) into motion. The motion can be rotary or linear, depending on the type of actuator. Some types of pneumatic actuators include:

This article includes a list of references or external links, but its sources remain unclear because it lacks inline citations. Please improve this article by introducing more precise citations where appropriate. (March 2008)

Electric actuator on a valve in a power plantActuators are used for the automation of industrial valves and can be found in all kinds of technical process plants: they are used in wastewater treatment plants, power plants and even refineries. This is where they play a major part in automating process control. The valves to be automated vary both in design and dimension. The diameters of the valves range from a few inches to a few metres.

Depending on their type of supply, the actuators may be classified as pneumatic, hydraulic, or electric actuators.

Contents [hide]
1 Classification of actuators according to their movement
1.1 Multi-turn actuators
1.2 Part-turn actuators
1.3 Linear actuators
2 Design
2.1 Motor (1)
2.2 Limit and torque sensors (2)
2.3 Gearing (3)
2.4 Valve attachment (4)
2.5 Manual operation (5)
2.6 Actuator controls (6)
2.7 Electrical connection (7)
2.8 Fieldbus connection (8)
3 Functions
3.1 Automatic switching off in the end positions
3.2 Safety functions
3.3 Process control functions
3.4 Diagnosis
4 Duty types
4.1 Open-close duty
4.2 Positioning duty
4.3 Modulating duty
5 Service conditions
5.1 Enclosure protection
5.2 Ambient temperatures
5.3 Explosion protection
6 Additional uses

[edit] Classification of actuators according to their movement
Travel means the distance the closing element within the valve has to cover to completely open or close that valve. Typical closing elements include butterfly, globe or gate valve discs. These three closing elements stand for the three basic movements required for covering the travel. The butterfly valve disc is operated by a 90° swivel movement from end position OPEN to CLOSED, the globe valve disc is operated by a rather short linear movement (stroke) while the gate valve disc movement covers the full diameter of the valve. Each movement type requires a specific actuator type.

Electric multi-turn actuator on a gate valve
[edit] Multi-turn actuators
Multi-turn actuators are required for the automation of multi-turn valves. One of the major representatives of this type is the gate valve. The basic requirements on multi-turn actuators are described in the standard EN ISO 5210 as follows:

"A multi-turn actuator is an actuator which transmits to the valve a torque for at least one full revolution. It is capable of withstanding thrust."

A valve stem is mounted to the gate valve disc. The multi-turn actuator moves the gate valve disc from OPEN to CLOSED and vice versa via a stem nut. To cover the complete valve travel, the so-called valve stroke, the actuator has to perform – depending on the valve – a few or several hundred rotations. Due to their design, the stroke of electric actuators, contrary to that of their pneumatic counterparts, has no limits. Therefore, gate valves are exclusively automated by means of electric multi-turn actuators.

The multi-turn actuator has to be able to withstand the weight of the gate valve disc by means of the valve attachment, the interface to the valve. This is expressed in the second sentence of the definition.

Gate valves may have a diameter of approx. 4 inches to several meters. The torque requirement for multi-turn solutions ranges from approx. 10 N m to 30,000 N m.

Electric part-turn actuator on a butterfly valve
[edit] Part-turn actuators
Part-turn actuators are required for the automation of part-turn valves. Major representatives of this type are butterfly valves and ball valves. The basic requirements on part-turn actuators are described in the standard EN ISO 5211 as follows:

"A part-turn actuator is an actuator which transmits a torque to the valve for less than one full revolution. It need not be capable of withstanding thrust."

Less than one full revolution usually means a swivel movement of 90°; however, there are some valve types requiring a different swing angle, such as two-way valves. The closing elements in part-turn actuators are always supported by the valve housing, i.e. the weight of the closing element does not act upon the part-turn actuator. This is expressed in the second sentence of the definition.

Part-turn valves diameters range from a few inches to several metres. The torque requirement for operating the closing element has a comparable range from approximately 10 N m to several 100,000 N m. Electric actuators are unrivalled for large-diameter valves with high torque requirements,.

[edit] Linear actuators
Currently there is no international standard describing linear actuators or linear thrust units. A typical representative of the valves to be automated is the control valve. Just like the plug in the bathtub is pressed into the drain, the plug is pressed into the plug seat by a stroke movement. The pressure of the medium acts upon the plug while the thrust unit has to provide the same amount of thrust to be able to hold and move the plug against this pressure.

Most of the linear actuators used are pneumatic diaphragm actuators. They are characterised by a simple design principle and are therefore cost-effective. A compressed air supply is a prerequisite for their use. In case this is not possible, the use of thrust units is recommended which can easily be supplied with power.

[edit] Design

Electric multi-turn actuator with controls
[edit] Motor (1)
Robust asynchronous 3-phase AC motors are mostly used as electric motors, for some applications also 1-phase AC or DC motors are used. The motors are specially adapted for valve automation requirements. Due to their design, they provide higher torques from standstill than comparable conventional motors. This feature is required to be able to unseat sticky valves. Electric actuators are used under extreme ambient conditions. Fan motors do not provide sufficient enclosure protection and can therefore not be used. Actuators can generally not be used for continuous operation since the motors have to cool down after a certain operating time. This suits the application since valves are not continuously operated.

[edit] Limit and torque sensors (2)
The limit switching measures the travel and signals when an end position has been reached, the torque switching measures the torque present in the valve. When exceeding a set limit, this is signalled in the same way. Actuators are often equipped with a remote position transmitter which indicates the valve position as continuous current or voltage signal.

[edit] Gearing (3)
Often a worm gearing is used to reduce the high output speed of the electric motor. This enables a high reduction ratio within the gear stage, leading to a low efficiency which is desired for the actuators. The gearing is therefore self-locking i.e. it prevents accidental and undesired changes of the valve position by acting upon the valve’s closing element. This is of major importance for multi-turn actuators which are axially loaded with the weight of the gate valve disc.

[edit] Valve attachment (4)
The valve attachment consists of two elements. First: The flange used to firmly connect the actuator to the counterpart on the valve side. The higher the torque to be transmitted, the larger the flange required.

Second: The output drive type used to transmit the torque or the thrust from the actuator to the valve shaft. Just like there is a multitude of valves there is also a multitude of valve attachments.

Dimensions and design of valve mounting flange and valve attachments are stipulated in the standards EN ISO 5210 for multi-turn actuators or EN ISO 5211 for part-turn actuators. The design of valve attachments for linear actuators is generally based on DIN 3358.

[edit] Manual operation (5)
In their basic version most electric actuators are equipped with a handwheel for operating the actuators during commissioning or power failure. The handwheel does not move during motor operation.

[edit] Actuator controls (6)
Both actuator signals and operation commands of the DCS are processed within the actuator controls. This task can in principle be assumed by external controls, e.g. a PLC. Modern actuators include integral controls which process signals locally without any delay. The controls also include the switchgear required to control the electric motor. This can either be reversing contactors or thyristors which, being an electric component, are not subject to mechanic wear. Controls use the switchgear to switch the electric motor on or off depending on the signals or commands present. Another task of the actuator controls is to provide the DCS with feedback signals, e.g. when reaching a valve end position.

[edit] Electrical connection (7)
The supply cables of the motor and the signal cables for transmitting the commands to the actuator and sending feedback signals on the actuator status are connected to the electrical connection. The electrical connection is ideally designed as plug/socket connector. For maintenance purposes, the wiring can easily be disconnected and reconnected.

[edit] Fieldbus connection (8)
Fieldbus technology is increasingly used for data transmission in process automation applications. Electric actuators can therefore be equipped with all common fieldbus interfaces used in process automation. Special connections are required for the connection of fieldbus data cables.

[edit] Functions

[edit] Automatic switching off in the end positions
After receiving an operation command, the actuator moves the valve in direction OPEN or CLOSE. When reaching the end position, an automatic switch-off procedure is started. Two fundamentally different switch-off mechanisms can be used. The controls switch off the actuator as soon as the set tripping point has been reached. This is called limit seating. However there are valve types for which the closing element has to be moved in the end position at a defined force or a defined torque to ensure that the valve seals tightly. This is called torque seating. The controls are programmed as to ensure that the actuator is switched off when exceeding the set torque limit. The end position signal of the limit switching is used for signalling the end position.

[edit] Safety functions
The torque switching is not only used for torque seating in the end position, but it also serves as overload protection over the whole travel and protects the valve against excessive torque. If excessive torque acts upon the closing element in an intermediate position, e.g. due to a trapped object, the torque switching will trip when reaching the set tripping torque. In this situation the end position is not signalled by the limit switching. The controls can therefore distinguish between normal operation torque switch tripping in one of the end positions and switching off in an intermediate position due to excessive torque.

Temperature sensors are required to protect the motor against overheating. For some applications by other manufacturers, the increase of the motor current is also monitored. Thermoswitches or PTC thermistors which are embedded in the motor windings mostly reliably fulfil this task. They trip when the temperature limit has been exceeded and the controls switch off the motor.

The positioner [1] is supplied with a setpoint [2] and an actual value [3]. The motor is controlled until the actual value is identical to the setpoint. The DCS generally needs a feedback signal [4]
[edit] Process control functions
Due to increasing decentralisation in automation technology and the introduction of micro processors, more and more functions have been transferred from the DCS to the field devices. The data volume to be transmitted was reduced accordingly, in particular by the introduction of fieldbus technology. Electric actuators whose functions have been considerably expanded are also affected by this development. The simplest example is the position control. Modern positioners are equipped with self-adaptation i.e. the positioning behaviour is monitored and continuously optimised via controller parameters.

Meanwhile, electric actuators are equipped with fully-fledged process controllers (PID controllers). Especially for remote installations, e.g. the flow control to an elevated tank, the actuator can assume the tasks of a PLC which otherwise would have to be additionally installed.

[edit] Diagnosis
The diagnostic function covers two aspects. Modern actuators have extensive diagnostic functions which help to identify the cause of a failure. The second function is the logging of operating data. The evaluation of the data allows to draw conclusions on the previous course of operation. Working on this basis, the operation can be optimised by changing the parameters and the wear of both actuator and valve be reduced.

[edit] Duty types

Typical time period in open-close duty. t1 is the operating time and may not exceed the maximum permissible running time
Typical time period in modulating duty.
[edit] Open-close duty
If valves are used as shut-off valves, the valve is either opened or closed. Intermediate positions are not approached. The valve is rarely operated, the interval between operations may be a few minutes or even several months.

The 'Short-time duty S2’ operation mode of the electric motor in accordance with the IEC 34-1 standard indicates that the actuator is suitable for this kind of applications. Another characteristic of this duty type is the maximum permissible running time without interruption. A typical time for actuators is 15 min.

[edit] Positioning duty
Defined intermediate positions are approached for setting a static flow through a pipeline. The same running time limits as in open-close duty apply.

[edit] Modulating duty
The most distinctive feature of a closed-loop application is that changing conditions require frequent adjustment of the MOV e.g. to set a certain flow rate. Sensitive closed-loop applications require adjustments within intervals of a few seconds. The demands on the actuator are higher than in open-close or positioning duty. Both mechanics and motor have to be designed as to be able to withstand the high number of starts without any deterioration in control accuracy.

The duty type of the electric motors suitable for this application is called intermittent duty S4 or intermittent duty S5. The running time is limited by the relative on-time; for modulating actuators this is usually 25 %.

Actuators are used in Siberia...
...and also in the Sahara
[edit] Service conditions
Electric actuators are used worldwide, in all climate zones, in all kinds of industrial plants under special local ambient conditions. The applications are often safety related, therefore the plant operators put high demands on the reliability of the devices. Failure of an actuator may cause accidents in process-controlled plants and toxic substances may leak into the environment.

Process-controlled plants are often operated for several decades which justifies the higher demands put on the lifetime of the devices.

For this reason, actuators are always designed in high enclosure protection. The manufacturers put a lot of work and knowledge into corrosion protection.

[edit] Enclosure protection
The enclosure protection types are defined according to the so-called IP codes of EN 60529. The basic version of most electric actuators is already designed in the second highest enclosure protection IP 67. This means they are protected against the ingress of dust and water during immersion (30 min at a max. head of water of 1 m). Most actuator manufacturers also supply devices in enclosure protection IP 68 which provide protection against submersion up to a max. head of water of 6 m.

[edit] Ambient temperatures
In Siberia, temperatures up to – 60 °C may occur, in technical process plants, + 100 °C may be exceeded. Using the proper lubricant is crucial for full operability under these conditions. Greases which may be used at room temperature will become too solid at low temperatures so that the actuator cannot overcome the resistance within the device. At high temperatures, these greases will liquify and lose their lubricating power. When sizing the actuator, the ambient temperature and the selection of the correct lubricant are of major importance.

[edit] Explosion protection
Electric actuators are used in applications where potentially explosive atmospheres may occur. This includes among others refineries, pipelines, oil and gas exploration or even mining. In case potentially explosive gas-air-mixtures or gas-dust-mixtures occur, the actuator may not act as ignition source. Basically, hot surfaces on the actuator as well as ignition sparks created by the actuator have to be avoided. This can be achieved by a flameproof enclosure, for example; i.e. the housing is designed as to prevent ignition sparks from leaving the housing even in case of an explosion inside.

Actuators designed for these applications, being explosion-proof devices, have to be qualified by a test authority (notified body). There is no such thing as a worldwide uniform standard: depending on the country where the actuators are used, different directives and regulations have to be observed. Within the European Union, ATEX 94/9/EC applies, in US, the NEC (approval by FM) or the CEC in Canada (approval by the CSA). Explosion-proof actuators have to meet the design requirements of these directives and regulations.

[edit] Additional uses
Small electric actuators can be used in a wide variety of assembly, packaging and testing applications. Such actuators can be linear, rotary, or a combination of the two, and can be combined to perform work in three dimensions. Such actuators are often used to replace pneumatic cylinders.

Hydraulic cylinder
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The hydraulic cylinders on this excavator control the machine's linkages.A Hydraulic cylinder (also called a linear hydraulic motor) is a mechanical actuator that is used to give a linear force through a linear stroke. It has many applications, notably in engineering vehicles.

Contents [hide]
1 Operation
2 Parts of a hydraulic cylinder
2.1 Cylinder barrel
2.2 Cylinder Bottom or Cap
2.3 Cylinder Head
2.4 Piston
2.5 Piston Rod
2.6 Rod Gland
2.7 Other parts
3 Hydraulic Cylinder Designs
3.1 Tie Rod Cylinders
3.2 Welded Body Cylinders
4 Piston Rod construction
4.1 Metallic coatings
4.2 Ceramic coatings
4.3 Lengths
5 Special hydraulic cylinders
5.1 Telescopic cylinder
5.2 Plunger cylinder
5.3 Differential cylinder
6 References
7 See also

[edit] Operation
Hydraulic cylinders get their power from pressurized hydraulic fluid, which is typically oil. The hydraulic cylinder consists of a cylinder barrel, in which a piston connected to a piston rod moves back and forth. The barrel is closed on each end by the cylinder bottom (also called the cap end) and by the cylinder head where the piston rod comes out of the cylinder. The piston has sliding rings and seals. The piston divides the inside of the cylinder in two chambers, the bottom chamber (cap end) and the piston rod side chamber (rod end). The hydraulic pressure acts on the piston to do linear work and motion. Flanges, trunnions, and/or clevisses are mounted to the cylinder body. The piston rod also has mounting attachments to connect the cylinder to the object or machine component that it is pushing.

A hydraulic cylinder is the actuator or "motor" side of this system. The "generator" side of the hydraulic system is the hydraulic pump which brings in a fixed or regulated flow of oil to the bottom side of the hydraulic cylinder, to move the piston rod upwards. The piston pushes the oil in the other chamber back to the reservoir. If we assume that the oil pressure in the piston rod chamber is approximately zero, the force on the piston rod equals the pressure in the cylinder times the piston area (F=PA).

The piston moves instead downwards if oil is pumped into the piston rod side chamber and the oil from the piston area flows back to the reservoir without pressure. The pressure in the piston rod area chamber is (Pull Force) / (piston area - piston rod area).

[edit] Parts of a hydraulic cylinder
A hydraulic cylinder consists of the following parts:

[edit] Cylinder barrel
The cylinder barrel is mostly a seamless thick walled forged pipe that must be machined internally. The cylinder barrel is ground and/or honed internally.

[edit] Cylinder Bottom or Cap
In most hydraulic cylinders, the barrel and the bottom are welded together. This can damage the inside of the barrel if done poorly. Therefore some cylinder designs have a screwed or flanged connection from the cylinder end cap to the barrel. (See "Tie Rod Cylinders" below) In this type the barrel can be disassembled and repaired in future.

[edit] Cylinder Head
The cylinder head is sometimes connected to the barrel with a sort of a simple lock (for simple cylinders). In general however the connection is screwed or flanged. Flange connections are the best, but also the most expensive. A flange has to be welded to the pipe before machining. The advantage is that the connection is bolted and always simple to remove. For larger cylinder sizes, the disconnection of a screw with a diameter of 300 to 600 mm is a huge problem as well as the alignment during mounting.

[edit] Piston
The piston is a short, cylinder-shaped metal component that separates the two sides of the cylinder barrel internally. The piston is usually machined with grooves to fit elastomeric or metal seals. These seals are often O-rings, U-cups or cast iron rings. They prevent the pressurized hydraulic oil from passing by the piston to the chamber on the opposite side. This difference in pressure between the two sides of the piston causes the cylinder to extend and retract. Piston seals vary in design and material according to the pressure and temperature requirements that the cylinder will see in service. Generally speaking, elastomeric seals made from nitrile rubber or other materials are best in lower temperature environments while seals made of Viton are better for higher temperatures. The best seals for high temperature are cast iron piston rings.

[edit] Piston Rod
The piston rod is typically a hard, chrome-plated piece of cold-rolled steel which attaches to the piston and extends from the cylinder through the rod-end head. In double rod-end cylinders, the actuator has a rod extending from both sides of the piston and out both ends of the barrel. The piston rod connects the hydraulic actuator to the machine component doing the work. This connection can be in the form of a machine thread or a mounting attachment such as a rod-clevis or rod-eye. These mounting attachments can be threaded or welded to the piston rod or, in some cases, they are a machined part of the rod-end.

[edit] Rod Gland
The cylinder head is fitted with seals to prevent the pressurized oil from leaking past the interface between the rod and the head. This area is called the rod gland. It often has another seal called a rod wiper which prevents contaminants from entering the cylinder when the extended rod retracts back into the cylinder. The rod gland also has a rod bearing. This bearing supports the weight of the piston rod and guides it as it passes back and forth through the rod gland. In some cases, especially in small hydraulic cylinders, the rod gland and the rod bearing are made from a single integral machined part.[1]

[edit] Other parts
Cylinder bottom connection
Seals
Cushions
A hydraulic cylinder should be used for pushing and pulling only. No bending moments or side loads should be transmitted to the piston rod or the cylinder. For this reason, the ideal connection of a hydraulic cylinder is a single clevis with a spherical ball bearing. This allows the hydraulic actuator to move and allow for any misalignment between the actuator and the load it is pushing.

[edit] Hydraulic Cylinder Designs
There are primarily two styles of hydraulic cylinder construction used in industry: tie rod style cylinders and welded body style cylinders.

[edit] Tie Rod Cylinders
Tie rod style hydraulic cylinders use high strength threaded steel rods to hold the two end caps to the cylinder barrel. This method of construction is most often seen in industrial factory applications. Small bore cylinders usually have 4 tie rods, while large bore cylinders may require as many as 16 or 20 tie rods in order to retain the end caps under the tremendous forces produced. Tie rod style cylinders can be completely disassembled for service and repair.[2]

The National Fluid Power Association (NFPA) has standardized the dimensions of hydraulic tie rod cylinders. This enables cylinders from different manufacturers to interchange within the same mountings.

[edit] Welded Body Cylinders
Welded body cylinders have no tie rods. The barrel is welded directly to the end caps. The ports are welded to the barrel. The front rod gland is usually threaded into or bolted to the cylinder barrel. This allows the piston rod assembly and the rod seals to be removed for service.

A Cut Away of a Welded Body Hydraulic Cylinder showing the internal components
Welded body cylinders have a number of advantages over tie rod style cylinders. Welded cylinders have a narrower body and often a shorter overall length enabling them to fit better into the tight confines of machinery. Welded cylinders do not suffer from failure due to tie rod stretch at high pressures and long strokes. The welded design also lends itself to customization. Special features are easily added to the cylinder body. These may include special ports, custom mounts, valve manifolds, and so on.[2]

The smooth outer body of welded cylinders also enables the design of multi-stage telescopic cylinders.

Welded body hydraulic cylinders dominate the mobile hydraulic equipment market such as construction equipment (excavators, bull dozers, and road graders) and material handling equipment (fork lift trucks, telehandlers, and lift gates). They are also used in heavy industry such as cranes, oil rigs, and above ground mining.

[edit] Piston Rod construction
The piston rod of a hydraulic cylinder operates both inside and outside the barrel, and consequently both in and out of the hydraulic fluid and surrounding atmosphere.

[edit] Metallic coatings
Smooth and hard surfaces are desirable on the outer diameter of the piston rod and slide rings for proper sealing. Corrosion resistance is also advantageous. A chromium layer may often be applied on the outer surfaces of these parts. However, chromium layers may be porous, thereby attracting moisture and eventually causing oxidation. In harsh marine environments, the steel is often treated with both a nickel layer and a chromium layer. Often 40 to 150 micrometer thick layers are applied. Sometimes solid stainless steel rods are used. High quality stainless steel such as AISI 316 may be used for low stress applications. Other stainless steels such as AISI 431 may also be used where there are higher stresses, but lower corrosion concerns.

[edit] Ceramic coatings
Due to shortcomings of metallic materials, ceramic coatings were developed. Initially ceramic protection schemes seemed ideal, but porosity was higher than projected. Recently the corrosion resistant semi ceramic Lunac 2+ coatings were introduced. These hard coatings are non porous and do not suffer from high brittleness.

[edit] Lengths
Piston rods are generally available in lengths which are cut to suit the application. As the common rods have a soft or mild steel core, their ends can be welded or machined for a screw thread.

[edit] Special hydraulic cylinders

[edit] Telescopic cylinder

Telescopic cylinder (ISO 1219 symbol)The length of a hydraulic cylinder is the total of the stroke, the thickness of the piston, the thickness of bottom and head and the length of the connections. Often this length does not fit in the machine. In that case the piston rod is also used as a piston barrel and a second piston rod is used. These kind of cylinders are called "telescopic cylinders". If we call a normal cylinder "one stroke", telescopic cylinders can be two, three, four, five and even six stroke. In general telescopic cylinders are much more expensive than normal cylinders. Most telescopic cylinders are single acting (push). Double acting telescopic cylinders must be specially designed and manufactured.

[edit] Plunger cylinder

Plunger cylinderA hydraulic cylinder without a piston or with a piston without seals is called a plunger cylinder. A plunger cylinder can only be used as a pushing cylinder; the maximum force is pistonrod area multiplied by pressure. This means that a piston cylinder in general has a relatively thick pistonrod.

[edit] Differential cylinder

Differential cylinder (ISO 1219 symbol)A differential cylinder acts like a normal cylinder when pulling. If the cylinder however has to push, the oil from the pistonrod side of the cylinder is not returned to the reservoir, but goes to the bottomside of the cylinder. In such a way, the cylinder goes much faster, but the maximum force the cylinder can give is like a plunger cylinder. A differential cylinder can be manufactured like a normal cylinder, and only a special control is added.

[edit] References
^ Hyco Canada Introduction to Hydraulic Cylinders
^ a b Hyco Ultrametal Advantages of Welded Cylinders Tutorial

Retrieved from "http://en.wikipedia.org/wiki/Hydraulic_cylinder"
Categories: Fluid dynamics | Hydraulics
Tutorial on Cylinders

Introduction to Hydraulic Cylinder Basics
Hydraulic cylinders convert the energy produced from a hydraulic pump into a linear mechanical output so that they can perform useful work.

Hydraulic cylinders are sometimes also referred to as hydraulic rams, hydraulic jacks, linear hydraulic actuators, and hydraulic actuators. These terms are all synonymous although the terms "hydraulic ram" and "hydraulic jack" are usually applied to short stroke, single acting cylinders with large diameter piston rods. Hydraulic cylinders are the muscles of machinery.

Above: A cut away diagram showing the internal components of a welded body hydraulic cylinder. Click on the image for a larger close up view.

Hydraulic cylinders are so named because they consist of a piston that moves through a smooth round cylinder or tube. This cylindrical tube must be sealed at both ends with end plates. The end plates are also called end caps or cylinder heads. The piston is firmly connected to a shaft called a piston rod that exits the cylinder through a hole in one end cap. This is called the rod end. The opposite end of the cylinder is called the cap end or the blind end (because it does not have an eye for the rod to stick out).

Above: A Cut Away Diagram of a Typical Hydraulic Cylinder Labelled with the Correct Component Names. Click on the image for a larger view.

The cylinder end caps also usually contain the ports where hydraulic fluid is admitted into the cylinder.

The piston rod is the working end of the cylinder and is usually fastened to a load that must be moved. The opposite end of the cylinder body is called the cap end or blind end. It is usually attached to a surface which the actuator pushes against although a large variety of mountings are available that can be mounted at various positions over the body of the actuator.

The cylinder barrel or tube is usually made from high strength seamless steel tubing that has been honed or skive roller burnished to a fine finish on the inside diameter. This will provide a smooth surface for the hydraulic piston to slide through. The tube must be of sufficient thickness to contain the hydraulic pressure that will be used. In a welded body hydraulic cylinder, the barrel must also provide the mechanical strength and rigidity to support the loads that the body of the actuator will see. This is especially true when a mid trunnion mount is attached to the center of the cylinder barrel.

Above: Large bore, high pressure, hydraulic cylinder barrels.

The amount of distance that a hydraulic cylinder is able to push the piston rod is called the cylinder stroke or travel.

The amount of force that a cylinder is able to produce is directly related to the area of the piston to which the hydraulic fluid is exposed and the pressure of the hydraulic fluid. The larger the piston area, the more force is produced. The higher the pressure of the hydraulic fluid, the more force is produced. This amount of force is also called the cylinder capacity. It is measured in Pounds of force (lbsf), Tons of force, Newtons of force (N), or Kilograms (Kgf) of force. This force capacity is determined using the basic mathematical formula F=PA, where F= Force, P= Pressure, and A= Area. this equation is easily manipulated to determine the correct size of a cylinder for a required force, or the hydraulic system pressure required to produce a force for a given cylinder.

It should be kept in mind that the effective piston area on the rod end of a hydraulic cylinder is reduced by the area of the piston rod. The piston rod area must be subtracted from the total piston area to find the effective area of the piston being used during the retraction stroke. The force of a cylinder produced while retracting (or pulling) will always be less than the force produced when the cylinder is extending. The larger the diameter of the piston rod, the greater effect it will have in reducing the force of the cylinder in retracting.

A rod cylinder with a large diameter piston rod will retract with much less force than on extension due to the area of the rod subtracting from the total area of the piston as on these oil field cylinders shown above.

Hydraulic cylinders are specified by bore size, stroke, mounting style, rod diameter, and pressure rating. Other details include seal material, temperature rating, materials of construction, cushioning, and more.
Hydraulic rod cylinders are often shown in machine diagrams by the following standardized ISO symbol:

Above: The Internationallt Recognized ISO Symbol for a Hydraulic Cylinder

Single Acting and Double Acting Hydraulic Cylinders
Hydraulic cylinders are designed to be either single acting or double acting.

A single acting hydraulic cylinder is the most simple and least expensive design. Pressurized hydraulic fluid is pumped into the cylinder at one end only and pushes the piston in one direction, usually to extend the rod. Once the work is accomplished, the oil is depressurized and diverted back to the oil reservoir. The piston is returned to its retracted position by an external force such as gravity or a compressed return spring. The piston of a single acting cylinder requires only one seal to contain the pressurized hydraulic fluid on the one side of the piston.

A double acting cylinder is more complicated as it uses pressurized hydraulic fluid to both extend and retract the piston rod. It thus requires fluid ports at both ends of the actuator in order for the oil to be directed onto both sides of the piston. The piston must therefore be equipped with seals that will contain the pressure from both sides. The hole from which the piston rod extends out of the one end of the actuator must also be sealed to prevent fluid pressure loss. This area is often called the rod gland. It also consists of a bearing surface to guide and support the piston rod as it moves back and forth. Another seal called a rod wiper is usually installed here to clean the rod as it re-enters the cylinder. The rod wiper excludes contamination that might damage the inner seals or the oil quality. Under extreme conditions a special hardened, heavy duty rod wiper called a rod scraper can be used to remove sticky contaminants from the piston rod as it re-enters the cylinder.

Welded Body Cylinders Versus Tie Rod Cylinders
There are two basic design styles of hydraulic cylinders: the welded cylinder and the tie rod cylinder.

The welded body hydraulic cylinder is built by welding the steel end caps to a heavy gauge steel tube. The rod gland is usually bolted or threaded to a flange welded to the rod end of the cylinder. This provides access to the inner workings of the actuator for disassembly and repair. The cap end of a welded cylinder, also sometimes called the blind end, is not removable.

Above: A typical welded body hydraulic cylinder.

Tie rod cylinders use high strength rods to hold the end caps onto the cylinder barrel. Small bore hydraulic cylinders, from 1 inch to 8 inch bore, usually have four tie rods holding the ends caps together. Large bore cylinders may require as many as 24 tie rods in order to retain the huge internal forces being generated.

Above: A typical tie rod construction hydraulic cylinder.

Welded body hydraulic cylinders have the advantage of being more compact is size than the tie rod design. Without the external tie rods and the wide heads to retain these rods, they are narrower in profile. Welding the heads to the barrel also reduces their overall length compared to tie rod cylinders.

Tie rod cylinders suffer from some disadvantages due to their design. At high pressures, the tie rods stretch slightly. On long stroke cylinders this stretch may add up to such an extent that the tube detaches from the end caps and a loss of pressure and fluid volume occurs. Long stroke tie rod cylinders also require intermediate heads to be installed along the body to support the tie rods from sagging. Finally, certain mounting styles can cause the end caps of a tie rod cylinder to misalign again causing a loss of fluid pressure and volume.

Special Hydraulic Cylinder Designs
Other cylinder designs have been conceived that incorporate the barrel crimped onto the end caps or using retaining rings inside tie tubes. These styles lack strength and durability and are thus usually limited to low pressures (less than 500 psi) and small sizes (less than 4 inch bore).

Other cylinder designs that are sometimes used are double rod end cylinders, multistage cylinders, tandem cylinders, and telescopic cylinders.

Double Rod End Cylinders

Double rod end cylinders have piston rods extending out both end caps. Thus when the piston is pushed down the barrel, one piston rod extends while the other is retracting.

This design is sometimes used when the actuator is mounted by the two rod ends and the load is fastened to the cylinder body. The load thus traverses back and forth with the cylinder body.

Another reason for using this design is to equalize the areas or volumes on both sides of the piston. The result is that the extend and retract speed and the forces produced in both directions will be exactly the same.

A double rod end cylinder also enables the user to attach devices to the back end of the cylinder to adjust the stroke of the actuator or to measure or indicate the distance travelled.

Multi-Stage Hydraulic Cylinders

Sometimes cylinders are assembled to provide several discrete, exactly repeatable strokes without the need for complicated feedback control systems. This can be accomplished by integrating two or more cylinders together to produce multiple stages of extension.

One multi-stage configuration consists of mounting two cylinders back to back by their rear heads. Thus when one cylinder (A) is extended, one discrete travel is produced. When the other cylinder (B) is extended, another discrete travel is produced. If the two cylinder bodies used are of different strokes, 4 discrete travels can be produced from the two actuators (0, A, B, and A+B).

If yet a third cylinder (C) is added to the assembly by attaching it to the rod end of cylinder B, AS many AS 8 discrete travels can be produced (0, A, B, A+B, C, A+C, B+C, A+B+C). Three cylinders are usually the limit to this assembly style due to cost, overall length, and weight considerations. Any more position requirements can be usually be provided more effectively by a feedback control system.

Another multi-stage cylinder configuration is produced by having cylinders mounted in sequence "nose to tail". In this arrangement a cylinder piston rod extends through the read head of another cylinder and pushes the piston of the front cylinder forward a discrete amount. In fact, numerous stages can be produced this way. Again, the disadvantages are cost, weight, and a build up of overall length.

Tandem Cylinders

Tandem cylinders are closely related to multistage cylinders but are used to produce a force multiplying output effect rather than a number of discrete stroke outputs. A tandem cylinder arrangement is often used when a large bore cylinder can not be fitted into a narrow space. Thus two or more cylinders mounted end to end are combined to push along the same line of force.

Telescopic Hydraulic Cylinders

Often cylinders are required to produce an long output travel from a very small retracted space. This would not be able to be accomplished using a standard rod style cylinder. Instead a series of hydraulic tubes nested like sleeves that telescope within each other are used to provide a long total output travel. Telescoping style cylinders are available in designs using 3, 4 or as many as 6 stages or sleeves. Travels of up to 500 inches can be provided.

Most telescopic cylinders are single acting cylinders. They are usually retracted using gravity. A typical example of a single acting telescopic cylinder is that which is used to tilt the dump body on the back of a dump truck.

Above: Two Telescopic Hydraulic Cylinders Tilt a Dump Body

Telescopic cylinders can be built as double acting cylinders too. These are much more complex and more expensive. They must be used carefully as the internal pressures produced if they are not retracted properly can burst the seals.

Telescoping cylinders must be carefully designed into each application. Because they often have such a long extended length, the application must ensure that the side loads exerted upon the cylinder bodies do not cause the unit to buckle and collapse.

Above: Long stroke telescopic cylinders must be carefully designed so as not to buckle under the forces they will see in service.

Never the less, telescoping hydraulic cylinders are a very effective solution to many actuator requirements that are not effectively solved using any other method or style of mechanism.
Hydraulic telescopic cylinders are often shown in machine diagrams by the following standardized ISO symbol:

Hydraulic Cylinder Cushions
Hydraulic cushioning can be provided to decelerate the cylinder load as it approaches the end of stroke. Cushions will prevent the piston from banging into the end caps with high impact forces. If not effectively cushioned, the resultant slamming could damage the piston and reduce the service life of the actuator.

Cushions are in fact small diameter pistons that enter a small receptacle machined into the end caps. As the cushion piston enters the cushion sleeve, the flow of hydraulic oil leaving the cylinder is restricted. This thereby slows down the speed of the actuator.

Above: A Cut Away View Showing a Hydraulic Cylinder Cushion

Care must be taken with the use of hydraulic cushions when combined with heavy loads. A very large moving mass will produce extremely high pressures within the cushion when the hydraulic flow is suddenly restricted. This spike in pressure may destroy the cylinder seals. In these situations, some other form of end of stroke deceleration should be incorporated into the machine design.

The addition of end of stroke cushioning may add to the overall length of a cylinder body and should therefore be considered before the design of any equipment is finalized.

Hydraulic cushions may not be available on the rod end of hydraulic cylinders with large diameter piston rods as the space required to accommodate the cushion sleeve is not available in the end cap.

Cylinders with large piston rods leave little room for a rod end cushion.

Cylinder heads with cushions usually have a built in check valve that allows the free flow of hydraulic fluid into the cylinder so that the speed of the cylinder will not be limited when the direction of travel is reversed. Cylinders with adjustable cushions will have needle valves mounted in the heads so that the flow of fluid leaving the cushion can be adjusted and the amount of deceleration fine tuned for the application.

Hydraulic Cylinder Mounting Options
Hydraulic actuators can be fitted with a wide variety of mounting styles to enable a designer to fit the cylinder into a machine. Mountings include fixed style mounts that hold the cylinder body rigidly in place and pivoting mounts that allow the body of the actuator to move with the machine components that it pushes.

Fixed mounting styles include front and rear flanges, threaded side tapped mounts, and foot mounts. These allow an actuator to be fasten to a flat surface such as a table or a steel plate.

Above: A Head Flange Mounted Hydraulic Actuator

Great care must be taken when using such fixed mounts so that the load does not exert side forces on the piston rod. Side loads on the piston rod will cause wear on the rod bearing, the inside diameter of the barrel, the outside diameter of piston, the rod seals, and the piston seals. A cylinder that encounters excessive side load forces will experience a short service life and require expensive repairs and machine downtime. Side loading may also cause high friction, binding and erratic cylinder movement.

The worst case scenario for a cylinder employing a fixed mount is when the load itself is being guided such as on a linear bearing or track. Any misalignment between the cylinder and movement of the load will produce side loads.

Above: A hydraulic cylinder with spherical eye mounts on both ends allowing the actuator to pivot and twist as it moves thus avoiding side loads.

A cylinder experiencing side loading will exhibit a dull surface finish on one side of the piston rod and a standard polished finish on the other side. Likewise the rod bearing, the piston and the inside diameter of the barrel will show asymmetrical wear patterns.

Pivoting mounts include rear pivot and rear clevis mounts, spherical eye mounts, and trunnion mounts. This mounts allow for misalignments by enabling the actuator to pivot or swing through an arc. Spherical mounts, although more expensive than clevis mounts, are especially effective as they also allow the cylinder to rotate slightly around its longitudinal axis.

Above: A Rear Clevis Mount Hydraulic Cylinder

Hydraulic Cylinder Piston Rods

The piston rod must be sized to accommodate the forces that the hydraulic actuator will produce. For example, a long stroke actuator with a small diameter piston rod, may fail in service if the rod buckles due to encountering forces that exceed its column strength.

At the same time, an oversized piston rod has disadvantages too. A large diameter piston rod has a higher initial cost. A cylinder with a large piston rod also requires a larger and more expensive mounting attachment. It is also heavier and will produce high end of stroke impact forces in a high velocity application. If it is too large it will not allow for end of stroke cushioning.

Finally, a large diameter piston rod will result in very high retraction speeds and reduced retraction forces. The high retraction speed is caused by the reduced volume on the rod end. The pump will take much less time to fill that small volume than the large volume on the cap end of the cylinder. The large rod reduces the effective area of the piston on the rod end resulting in smaller retraction forces.

With these points in mind, it is important to size a hydraulic cylinder piston rod properly for each application.

Speed Control of Hydraulic Cylinders
The speed of advance of the piston rod is adjusted by controlling the flow of hydraulic oil entering or leaving the cylinder. This is accomplished using valves. In simple systems that have one set speed of advance, the required speed is set by manually adjusting a needle valve mounted on the oil return line from the cylinder. This valve restricts the flow of oil exiting the cylinder thereby controlling the speed of advance. This needle valve often has an integral check valve allowing a free flow of oil in the opposite direction. Thus the cylinder can be rapidly retracted without restriction or it can have another valve set to control the retracting speed.

In more complex systems requiring constant cylinder speed adjustments, this is accomplished using the hydraulic fluid directional control servo valves. These valves allow an infinite adjustment of the volume of oil flow to the hydraulic actuator thus controlling cylinder output velocity. These valves are available with either manual control, usually by levers, or electronic control for interfacing with computers.

The Advantage of Hydraulic Cylinders
The primary advantage of hydraulic cylinders is that they enable large amounts of power to be applied to machinery in areas located remote from the large heavy source of power generation. This source of power is usually an electric motor, a diesel engine, a turbine, or, in very simple systems, a hand or foot pump.

Another advantage of hydraulic actuators is the incredible power to weight ratio and power to size ratio that they possess. Even a small hydraulic actuator weighing only a few pounds can exert a tremendous force. For example, a 2 inch bore, 4 inch stroke actuator, will have an outside diameter of less than 2.5 inches, an overall length of only about 12 inches, will weigh only about 10 pounds, but will produce over 6000 pounds (3 tons) of force when pressurized to 2000 psi.

Above: Hydraulic Actuators are Powerful and Rugged

Other advantages of hydraulic actuators include infinitely variable speed control, infinitely variable positioning, ability to hold large masses in place, and automatic overload protection. Hydraulic systems are rugged and are able endure difficult conditions. The technology is mature and used worldwide.

Applications of Hydraulic Cylinders
By combining hydraulic actuators with other mechanical devices including linkages, gears and valves, the applications are virtually limitless and confined only by ones ingenuity and imagination. Linear travel can be converted to rotary or oscillating motion. Travel and forces can be multiplied. Positioning and velocities can be controlled, changed and held.

From Wikipedia, the free encyclopedia
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A linear actuator is a device that develops force and motion, from an available energy source, in a linear manner, as opposed to rotationally like an electric motor. There are various methods of achieving this linear motion. Several different examples are listed below.

Contents [hide]
1 Types of Linear Actuators
1.1 Mechanical actuators
1.2 Hydraulic actuators
1.3 Piezoelectric actuators
1.4 Electro-mechanical actuators
1.4.1 Simplified Design
1.4.2 Principles
1.4.3 Variations
1.5 Linear motors
1.6 Wax motors
1.7 Segmented spindles
2 Advantages and Disadvantages
3 See also
4 References
5 External links

[edit] Types of Linear Actuators

[edit] Mechanical actuators

A mechanical linear actuator with digital readout.Mechanical actuators typically convert rotary motion of a control knob or handle into linear displacement via screws and/or gears to which the knob or handle is attached. A jackscrew or car jack is a familiar mechanical actuator. Another family of actuators are based on the segmented spindle. Rotation of the jack handle is converted mechanically into the linear motion of the jack head. Mechanical actuators are also frequently used in the field of lasers and optics to manipulate the position of linear stages, rotary stages, mirror mounts, goniometers and other positioning instruments. For accurate and repeatable positioning, index marks may be used on control knobs. Some actuators even include an encoder and digital position readout.[1] These are similar to the adjustment knobs used on micrometers except that their purpose is position adjustment rather than position measurement.

[edit] Hydraulic actuators
Hydraulic actuators or hydraulic cylinders typically involve a hollow cylinder having a piston inserted in it. The two sides of the piston are alternately pressurized/de-pressurized to achieve controlled precise linear displacement of the piston and in turn the entity connected to the piston. The physical linear displacement is only along the axis of the piston/cylinder. This design is based on the principles of hydraulics. A familiar example of a manually operated hydraulic actuator is a hydraulic car jack. Typically though, the term "hydraulic actuator" refers to a device controlled by a hydraulic pump.

[edit] Piezoelectric actuators
The piezoelectric effect is a property of certain materials in which application of a voltage to the material causes it to expand. Very high voltages correspond to only tiny expansions. As a result, piezoelectric actuators can achieve extremely fine positioning resolution, but also have a very short range of motion. In addition, piezoelectric materials exhibit hysteresis which makes it difficult to control their expansion in a repeatable manner.

[edit] Electro-mechanical actuators

Conceptual design of a basic linear actuator. Note that in this example the lead screw (gray) rotates while the lead nut (yellow) and tube (red) do not.
A miniature electro-mechanical linear actuator where the lead nut is part of the motor. The lead screw does not rotate, so as the lead nut is rotated by the motor, the lead screw is extended or retracted.
Typical compact cylindrical linear electric actuator
Typical linear or rotary + linear electric actuator

Moving coil linear, rotary and linear + rotary actuators at work in various applications.Electro-mechanical actuators are similar to mechanical actuators except that the control knob or handle is replaced with an electric motor. Rotary motion of the motor is converted to linear displacement of the actuator. There are many designs of modern linear actuators and every company that manufactures them tends to have their own proprietary method. The following is a generalized description of a very simple electro-mechanical linear actuator.

[edit] Simplified Design
Typically, a rotary driver (e.g. electric motor) is mechanically connected to a lead screw so that the rotation of the electric motor will make the lead screw rotate. A lead screw has a continuous helical thread machined on its circumference running along the length (similar to the thread on a bolt). Threaded onto the lead screw is a lead nut with corresponding helical threads. The nut is prevented from rotating with the lead screw (typically the nut interlocks with a non-rotating part of the actuator body). Therefore, when the lead screw is rotated, the nut will be driven along the threads. The direction of motion of the nut will depend on the direction of rotation of the lead screw. By connecting linkages to the nut, the motion can be converted to usable linear displacement. Most current actuators are built either for high speed, high force, or a compromise between the two. When considering an actuator for a particular application, the most important specifications are typically travel, speed, force, and lifetime.

[edit] Principles
In the majority of linear actuator designs, the basic principle of operation is that of an inclined plane. The threads of a lead screw act as a continuous ramp that allows a small rotational force to be used over a long distance to accomplish movement of a large load over a short distance.

[edit] Variations
Many variations on the basic design have been created. Most focus on providing general improvements such as a higher mechanical efficiency, speed, or load capacity. There is also a large engineering movement towards actuator miniaturization.

Most electro-mechanical designs incorporate a lead screw and lead nut. Some use a ball screw and ball nut. In either case the screw may be connected to a motor or manual control knob either directly or through a series of gears. Gears are typically used to allow a smaller (and weaker) motor spinning at a higher rpm to be geared down to provide the torque necessary to spin the screw under a heavier load than the motor would otherwise be capable of driving directly. Effectively this sacrifices actuator speed in favor of increased actuator thrust. In some applications the use of worm gear is common as this allow a smaller built in dimension still allowing great travel length.

Some lead screws have multiple "starts". This means that they have multiple threads alternating on the same shaft. One way of visualizing this is in comparison to the multiple color stripes on a candy cane. This allows for more adjustment between thread pitch and nut/screw thread contact area, which determines the extension speed and load carrying capacity (of the threads), respectively.

[edit] Linear motors
A linear motor is essentially a rotary electric motor laid down on flat surface. Since the motor moves in a linear fashion to begin with, no lead screw is needed to convert rotary motion to linear. While high capacity is possible, the material and/or motor limitations on most designs are surpassed relatively quickly. Most linear motors have a relatively low load capacity compared to other types of linear actuators.

[edit] Wax motors
A wax motor typically uses an electric current to heat a block of wax causing it to expand. A plunger that bears on the wax is thus forced to move in a linear fashion.

[edit] Segmented spindles
Segmented actuators consist of discrete chain elements which are interlinked to form a rod (the technology is known as the segmented spindle) thus making the actuator extremely compact.

[edit] Advantages and Disadvantages
Actuator Type Advantages Disadvantages
Mechanical Cheap. Repeatable. No power source required. Self contained. Identical behaviour extending or retracting. Manual operation only. No automation.
Electro-mechanical Cheap. Repeatable. Operation can be automated. Self contained. Identical behaviour extending or retracting. DC or Stepping motors. Position feedback possible. Many moving parts prone to wear.
Linear motor Simple design. Minimum of moving parts. High speeds possible. Self contained. Identical behaviour extending or retracting. Relatively low force.
Piezoelectric Very small motions possible. Requires position feedback to be repeatable. Short travel. Low speed. High voltages required. Expensive. Good in compression only. Not good in tension.
Hydraulic Very high forces possible. Can leak. Requires position feedback for repeatability. External hydraulics pump required. Some designs good in compression only.
Wax motor Smooth operation. Not as reliable as other methods.
Segmented spindle Very compact. Range of motion greater than length of actuator. Both linear and rotary motion.
Moving coil Force, position and speed are controllable and repeatable. Capable of high speeds and precise positioning. Linear, rotary, and linear + rotary actions possible. Requires position feedback to be repeatable.
MICA High Force and controllable. Higher force and less losses than moving coils [2]. Losses easy to dissipate. Electronic driver easy to design and set up. Stroke limited to several millimeters, less linearity than moving coils

[edit] See also
Linear motor
Wax motor
Pneumatics

[edit] References

Hydraulic motor
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A Hydraulic motor is a mechanical actuator that converts hydraulic pressure and flow into torque and angular displacement (rotation). The hydraulic motor is the rotary counterpart of the hydraulic cylinder.

Hydraulic motorConceptually, a hydraulic motor should be interchangeable with a hydraulic pump because it performs the opposite function - much as the conceptual DC electric motor is interchangeable with a DC electrical generator. However, most hydraulic pumps cannot be used as hydraulic motors because they cannot be backdriven. Also, a hydraulic motor is usually designed for the working pressure at both sides of the motor.

Hydraulic pumps, motors, and cylinders can be combined into hydraulic drive systems. One or more hydraulic pumps, coupled to one or more hydraulic motors, constitutes a hydraulic transmission.

Contents [hide]
1 Hydraulic motor types
1.1 Gear and vane motors
1.2 Axial plunger motors
1.3 Radial plunger motors
2 Braking
3 Uses
4 See also

[edit] Hydraulic motor types
For an explanation of plunger and piston, see hydraulic cylinder
Many designs are possible. The following types of hydraulic motors are available:

[edit] Gear and vane motors
Gear and vane motors are used in simple rotating systems that may be used occasionally.

[edit] Axial plunger motors
For high quality rotating drive systems plunger motors are generally used. Whereas the speed of hydraulic pumps ranges from 1200 to 1800 rpm, the machinery to be driven by the motor often requires a much lower speed. This means that when an axial plunger motor (swept volume maximum 2 litres) is used, a gearbox is usually needed. For a continuously adjustable swept volume, axial piston motors are used. PISTON TYPE.— Like piston (reciprocating) type pumps, the most common design of the piston type of motor is the axial. This type of motor is the most commonly used in hydraulic systems.

[edit] Radial plunger motors
Radial piston motors can not be obtained with very large swept volumes. Sometimes because the total piston volume of the pump is large (up to 8-9 litres), sometimes because the pistons move more than one time each revolution (up to 250 litres working swept volume). By decreasing the swept volume of the motor, the speed increases and the maximum torque decreases. Radial motors can get an adjustable swept volume by switching off some of the plungers.

[edit] Braking
Hydraulic motors usually have a leakage connection, which means that a hydraulic motor in a drive system can never hold the load, like a hydraulic cylinder can. There is always a need for a brake or a locking device.

[edit] Uses
Hydraulic motors are used for winch and crane drives and as wheel motors for military vehicles, self-driven cranes, and excavators. A very useful application is in field of Hydraulic Cranes.

[edit] See also

Hydraulic pump
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Gearpump with external teeth
Gearpump with internal teeth
A gerotor (image does not show intake or exhaust)
Fixed displacement vane pump
Principle of screw pump
Axial piston pump, swashplate principle
Radial piston pumpA Hydraulic is used in hydraulic drive systems.

Hydraulic pumps can be hydrostatic or hydrodynamic.

Hydrostatic pumps are positive displacement pumps.

Hydrostatic pumps can be fixed displacement pumps, in which the displacement (flow through the pump per rotation of the pump) cannot be adjusted, or variable displacement pumps, which have a more complicated construction that allows the displacement to be adjusted.

Contents [hide]
1 Hydraulic pump types
1.1 Gear pumps
1.2 Gerotor pumps
1.3 Rotary vane pumps
1.4 Screw pumps
1.5 Bent axis pumps
1.6 Axial piston pumps swashplate principle
1.7 Radial piston pumps
1.8 Peristaltic pumps
2 Pumps for open and closed systems
3 Multi pump assembly
4 Hydraulic pumps, calculation formulas
4.1 Flow
4.2 Power
5 See also

[edit] Hydraulic pump types

[edit] Gear pumps
Gear pumps (with external teeth) (fixed displacement) are simple and economical pumps. The swept volume or displacement of gear pumps for hydraulics will be between about 1 cm3 (0.001 litre) and 200 cm3 (0.2 litre). These pumps create pressure through the meshing of the gear teeth, which forces fluid around the gears to pressurize the outlet side. Some gear pumps can be quite noisy, compared to other types, but modern gear pumps are highly reliable and much more efficient than older models.

[edit] Gerotor pumps
Gerotor pumps (fixed displacement) are a variation of gear pumps, having internal teeth of optimized design. The efficiency and noise level are very good for such a medium pressure pump.

[edit] Rotary vane pumps
Rotary vane pumps (fixed and simple adjustable displacement) have higher efficiencies than gear pumps, but are also used for mid pressures up to 180 bars in general. Some types of vane pumps can change the centre of the vane body, so that a simple adjustable pump is obtained. These adjustable vane pumps are in general constant pressure or constant power pumps: the displacement is increased until the required pressure or power is reached and subsequently the displacement or swept volume is decreased until an equilibrium is reached.

[edit] Screw pumps
Screw pumps (fixed displacement) are a double Archimedes spiral, but closed. This means that two screws are used in one body. The pumps are used for high flows and relatively low pressure (max 100 bar). They were used on board ships where the constant pressure hydraulic system was going through the whole ship, especially for the control of ball valves, but also for the steering gear and help drive systems. The advantage of the screw pumps is the low sound level of these pumps; the efficiency is not that high.

[edit] Bent axis pumps
Bent axis pumps (axial piston pumps using the bent axis principle) (fixed and adjustable displacement) have the best efficiency of all pumps. Although in general the largest displacements are approximately one litre per revolution, if necessary a two liter swept volume pump can be built. Often variable displacement pumps are used, so that the oil flow can be adjusted carefully. These pumps can in general work with a working pressure of up to 350 bars.

[edit] Axial piston pumps swashplate principle
Axial piston pumps using the swashplate principle (fixed and adjustable displacement) have a quality that is almost the same as the bent axis model. They have the advantage of being more compact in design. The pumps are easier and more economical to manufacture; the disadvantage is that they are more sensitive to oil contamination.

[edit] Radial piston pumps
Radial piston pumps (fixed displacement) are used especially for high pressure and relatively small flows. Pressures of up to 650 bar are normal. In fact variable displacement is not possible, but sometimes the pump is designed in such a way that the plungers can be switched off one by one, so that a sort of variable displacement pump is obtained.

[edit] Peristaltic pumps
Peristaltic pumps are not generally used for high pressures.

[edit] Pumps for open and closed systems
Most pumps are working in open systems. The pump draws oil from a reservoir at atmospheric pressure. It is very important that there is no cavitation at the suction side of the pump. For this reason the connection of the suction side of the pump is larger in diameter than the connection of the pressure side. In case of the use of multi-pump assemblies, the suction connection of the pump is often combined. It is preferred to have free flow to the pump (pressure at inlet of pump at least 0.8 bars). The body of the pump is often in open connection with the suction side of the pump.

In case of a closed system, both sides of the pump can be at high pressure. The reservoir is often pressurized with 6-20 bars boost pressure. For closed loop systems, normally axial piston pumps are used. Because both sides are pressurized, the body of the pump needs a separate leakage connection.

[edit] Multi pump assembly
In a hydraulic installation, one pump can serve more cylinders and motors. The problem however is that in that case a constant pressure system is required and the system always needs the full power. It is more economic to give each cylinder and motor its own pump. In that case multi pump assemblies can be used. Gearpumps can often be obtained as multi pumps. The different chambers (sometimes of different size) are mounted in one body or built together. Also vane pumps can often be obtained as a multi pump. Gerotor pumps are often supplied as multi pumps. Screw pumps can be built together with a gear pump or a vane pump. Axial piston swashplate pumps can be built together with a second pump of the same or smaller size, or can be built together with one or more gear pumps or vane pumps (depending on the supplier). Axial plunger pumps of the bent axis design can not be built together with other pumps.

[edit] Hydraulic pumps, calculation formulas

[edit] Flow
Q = n * Vstroke *? vol
Q = Flow in m3/s
n = revs per second
Vstroke = swept volume in m3
? vol is volumetric efficiency

[edit] Power
P = n * Vstroke * ?p / ?mech,hydr
P = Power in Watt (Nm/s)
n = revs per second.
Vstroke = swept volume in m3
?p = pressure difference over pump in N/m2
?mech,hydr = mechanical/hydraulic efficiency

[edit] See also
[hide]v • d • eHydraulics

Concepts Hydraulics · Hydraulic fluid · Fluid power · Hydraulic engineering

Technologies Machinery · Accumulator · Brake · Circuit · Cylinder · Drive system · Manifold · Motor · Power network · Press · Pump · Ram · Rescue tools
Hydraulic drive system
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A hydraulic or hydrostatic drive system or hydraulic power transmission is a drive- or transmission system that use of a hydraulic fluid under pressure to drive machinery.

Such a system basically consists of:

Generator part of the transmission, in general a hydraulic pump, driven by an electric motor, a combustion engine or a windmill.
Valves, filters, piping etc. to guide and control the system
Motor part of the transmission a hydraulic motor or hydraulic cylinder to drive the machinery.
Hydrostatic means that the energy comes from the flow and the pressure, but not from the kinetic energy of the flow.

Contents [hide]
1 Principle of a hydraulic drive
2 Hydraulic cylinder
3 Hydraulic motor
4 Hydraulic valves
5 Hydraulic piping
6 Open and closed systems
7 See also
8 External links

[edit] Principle of a hydraulic drive

Principle of hydraulic drive systemPascal's law is the basis of hydraulic drive systems. As the pressure in the system is the same, the force that the fluid gives to the surroundings is therefore equal to pressure x area. In such a way, a small piston feels a small force and a large piston feels a large force.
The same counts for a hydraulic pump with a small swept volume, that asks for a small torque, combined with a hydraulic motor with a large sweptvolume, that gives a large torque.

In such a way a transmission with a certain ratio can be built.

Most hydraulic drive systems make use of hydraulic cylinders. Here the same principle is used- a small torque can be transmitted in to a large force.

By throttling the fluid between generator part and motor part, or by using hydraulic pumps and/or motors with adjustable swept volume, the ratio of the transmission can be changed easily. In case throttling is used, the efficiency of the transmission is limited; in case adjustable pumps and motors are used, the efficiency however is very large. In fact, up to around 1980, a hydraulic drive system had hardly any competition from other adjustable (electric) drive systems.

Nowadays electric drive systems using electric servo-motors can be controlled in an excellent way and can easily compete with rotating hydraulic drive systems. Hydraulic cylinders are in fact without competition for linear (high) forces. For these cylinders anyway hydraulic systems will remain of interest and if such a system is available, it is easy and logical to use this system also for the rotating drives of the cooling systems.

[edit] Hydraulic cylinder
Main article: Hydraulic cylinder
Hydraulic cylinders (also called linear hydraulic motors) are mechanical actuators that are used to give a linear force through a linear stroke. A hydraulic cylinder is without doubt the best known hydraulic component. Hydraulic cylinders are able to give pushing and pulling forces of millions of metric tons, with only a simple hydraulic system. Very simple hydraulic cylinders are used in presses; here the cylinder consists out of a volume in a piece of iron with a plunger pushed in it and sealed with a cover. By pumping hydraulic fluid in the volume, the plunger is pushed out with a force of plunger-area * pressure.

More sophisticated cylinders have a body with end cover, a piston-rod with piston and a cylinder-head. At one side the bottom is for instance connected to a single clevis, whereas at the other side, the piston rod also is foreseen with a single clevis. The cylinder shell normally has hydraulic connections at both sides. A connection at bottom side and one at cylinder head side. If oil is pushed under the piston, the piston-rod is pushed out and oil that was between the piston and the cylinder head is pushed back to the oil-tank again.

The pushing or pulling force of a hydraulic cylinder is:

F = Ab * pb - Ah * ph
F = Pushing Force in N
Ab = (p/4) * (Bottom-diameter)^2 [in m2]
Ah = (p/4) * ((Bottom-diameter)^2-(Piston-rod-diameter)^2)) [in m2]
pb = pressure at bottom side in [N/m2]
ph = pressure at cylinder head side in [N/m2]

Apart from miniature cylinders, in general, the smallest cylinder diameter is 32 mm and the smallest piston rod diameter is 16 mm.

Simple hydraulic cylinders have a maximum working pressure of say 70 bar, the next step is 140 bar, 210 bar, 320/350 bar and further, the cylinders are in general custom build. The stroke of a hydraulic cylinder is limited by the manufacturing process. The majority of hydraulic cylinders have a stroke between 0,3 and 5 metres, whereas 12-15 metre stroke is also possible, but for this length only a limited number of suppliers are on the market.

In case the retracted length of the cylinder is too long for the cylinder to be build in the structure. In this case telescopic cylinders can be used. One has to realize that for simple pushing applications telescopic cylinders might be available easily; for higher forces and/or double acting cylinders, they must be designed especially and are very expensive. If hydraulic cylinders are only used for pushing and the piston rod is brought in again by other means, one can also use plunger cylinders. Plunger cylinders have no sealing over the piston, or the piston does not exist. This means that only one oil connection is necessary. In general the diameter of the plunger is rather large compared with a normal piston cylinder, because this large area is needed.

Whereas a hydraulic motor will always leak oil, a hydraulic cylinder does not have a leakage over the piston nor over the cylinder head sealing, so that there is no need for a mechanical brake.

[edit] Hydraulic motor
Main article: Hydraulic motor
The hydraulic motor is the rotary counterpart of the hydraulic cylinder.

Conceptually, a hydraulic motor should be interchangeable with hydraulic pump, because it performs the opposite function -- much as the conceptual DC electric motor is interchangeable with a DC electrical generator. However, most hydraulic pumps cannot be used as hydraulic motors because they cannot be backdriven. Also, a hydraulic motor is usually designed for the working pressure at both sides of the motor.

[edit] Hydraulic valves
These valves are usually very heavy duty to stand up to high pressures. Some special valves can control the direction of the flow of fluid and act as a control unit for a system.

[edit] Hydraulic piping

[edit] Open and closed systems

Principle circuit diagram for open loop and closed loop system.
[edit] See also
[hide]v • d • eHydraulics

Concepts Hydraulics · Hydraulic fluid · Fluid power · Hydraulic engineering

Technologies Machinery · Accumulator · Brake · Circuit · Cylinder · Drive system · Manifold · Motor · Power network · Press · Pump · Ram · Rescue tools

[edit] External linksPumped-storage hydroelectricity
From Wikipedia, the free encyclopedia
Jump to: navigation, search
Hydro-storage redirects here. For storage of water for other purposes, see Reservoir.

Diagram of the TVA pumped storage facility at Raccoon Mountain Pumped-Storage Plant

Power spectrum of a pumped-storage hydroelectricity. Green represents power consumed in pumping; red is power generated.
Energy portal

Pumped storage hydroelectricity is a type of hydroelectric power generation used by some power plants for load balancing. The method stores energy in the form of water, pumped from a lower elevation reservoir to a higher elevation. Low-cost off-peak electric power is used to run the pumps. During periods of high electrical demand, the stored water is released through turbines. Although the losses of the pumping process makes the plant a net consumer of energy overall, the system increases revenue by selling more electricity during periods of peak demand, when electricity prices are highest. Pumped storage is the largest-capacity form of grid energy storage now available.

Contents [hide]
1 Overview
2 Potential technologies
3 Worldwide list of pumped storage plants
4 References
5 See also
6 External links

[edit] Overview
At times of low electrical demand, excess generation capacity is used to pump water into the higher reservoir. When there is higher demand, water is released back into the lower reservoir through a turbine, generating electricity. Reversible turbine/generator assemblies act as pump and turbine (usually a Francis turbine design). Some facilities use abandoned mines as the lower reservoir, but many use the height difference between two natural bodies of water or artificial reservoirs. Pure pumped-storage plants just shift the water between reservoirs, but combined pump-storage plants also generate their own electricity like conventional hydroelectric plants through natural stream-flow. Plants that do not use pumped-storage are referred to as conventional hydroelectric plants; conventional hydroelectric plants that have significant storage capacity may be able to play a similar role in the electrical grid as pumped storage, by deferring output until needed.

Taking into account evaporation losses from the exposed water surface and conversion losses, approximately 70% to 85% of the electrical energy used to pump the water into the elevated reservoir can be regained.[1] The technique is currently the most cost-effective means of storing large amounts of electrical energy on an operating basis, but capital costs and the presence of appropriate geography are critical decision factors.

The relatively low energy density of pumped storage systems requires either a very large body of water or a large variation in height. For example, 1000 kilograms of water (1 cubic meter) at the top of a 100 meter tower has a potential energy of about 0.272 kW·h. The only way to store a significant amount of energy is by having a large body of water located on a hill relatively near, but as high as possible above, a second body of water. In some places this occurs naturally, in others one or both bodies of water have been man-made.

This system may be economical because it flattens out load variations on the power grid, permitting thermal power stations such as coal-fired plants and nuclear power plants and renewable energy power plants that provide base-load electricity to continue operating at peak efficiency (Base load power plants), while reducing the need for "peaking" power plants that use costly fuels. Capital costs for purpose-built hydrostorage are high, however.

Along with energy management, pumped storage systems help control electrical network frequency and provide reserve generation. Thermal plants are much less able to respond to sudden changes in electrical demand, potentially causing frequency and voltage instability. Pumped storage plants, like other hydroelectric plants, can respond to load changes within seconds.

The upper reservoir (Llyn Stwlan) and dam of the Ffestiniog Pumped Storage Scheme in north Wales. The lower power station has four water turbines which generate 360 MW of electricity within 60 seconds of the need arising. The size of the dam can be judged from the car parked below.The first use of pumped storage was in the 1890s in Italy and Switzerland. In the 1930s reversible hydroelectric turbines became available. These turbines could operate as both turbine-generators and in reverse as electric motor driven pumps. The latest in large-scale engineering technology are variable speed machines for greater efficiency. These machines generate in synchronisation with the network frequency, but operate asynchronously (independent of the network frequency) as motor-pumps.

A new use for pumped storage is to level the fluctuating output of intermittent power sources. The pumped storage absorbs load at times of high output and low demand, while providing additional peak capacity. In certain jurisdictions, electricity prices may be close to zero or occasionally negative (Ontario in early September, 2006), indicating there is more generation than load available to absorb it; although at present this is rarely due to wind alone, increased wind generation may increase the likelihood of such occurrences. It is particularly likely that pumped storage will become especially important as a balance for very large scale photovoltaic generation.[2]

In 2000 the United States had 19.5 GW of pumped storage capacity, accounting for 2.5% of baseload generating capacity. PHS generated (net) -5.5 GWh of energy[3] because more energy is consumed in pumping than is generated; losses occur due to water evaporation, electric turbine/pump efficiency, and friction.

In 1999 the EU had 32 GW capacity of pumped storage out of a total of 188 GW of hydropower and representing 5.5% of total electrical capacity in the EU.

[edit] Potential technologies
The use of underground reservoirs as lower dams has been investigated. Salt mines could be used, although ongoing and unwanted dissolution of salt could be a problem. If they prove affordable, underground systems might greatly expand the number of pumped storage sites. Saturated brine is about 20% denser than fresh water.

A new concept in pumped storage is to utilise wind turbines or solar power to drive water pumps directly, in effect an 'Energy Storing Wind or Solar Dam'. This could provide a more efficient process and usefully smooth out the variabilities of energy captured from the wind or sun [4] [5].

One can use sea water in the dam.

[edit] Worldwide list of pumped storage plants
Argentina
Rio Grande-Cerro Pelado Hydroelectric Complex (1986), 750 MW
Australia
Bendeela (1977), 80 MW
Kangaroo Valley (1977), 160 MW
Tumut Three (1973), 1,500 MW
Wivenhoe Power Station, 510 MW
Austria
Häusling (1988), 360 MW
Lünerseewerk (1958), 232 MW
Kraftwerksgruppe Fragant, 100 MW
Kühtai (1981), 250 MW
Malta-Hauptstufe (1979), 730 MW
Rodundwerk I (1952), 198 MW
Rodundwerk II (1976), 276 MW
Roßhag (1972), 231 MW
Silz (1981), 500 MW
Belgium
Coo (1979), 110 MW
Plate Taille (1981), 136 MW
Bulgaria
PAVEC Belmeken (197?), 375 MW
PAVEC Chaira (1998), 864 MW
Canada
Sir Adam Beck Hydroelectric Power Stations, Niagara Falls (1957), 174 MW - reversible Deriaz turbines
China
Guangzhou (2000), 2,400 MW
Tianhuangping (2001), 1,800 MW
Croatia
CHE Fužine (1957). 4.6 MW
RHE Lepenica (1985), 1.14/1.25 MW[6]
RHE Velebit (1984), 276/240MW[7]
Czech Republic
Dalešice (1978), 480 MW
Dlouhé Stráne (1996), 650 MW
Štechovice (1947), 45 MW
France
Grand Maison (1997), 1,070 MW
La Coche (1976), 285 MW
Le Cheylas (1979), 485 MW
Montézic (1983), 920 MW
Rance (1966), 240 MW hybrid pumped water-tidal plant
Revin (1976), 800 MW
Super Bissorte (1978), 720 MW
Germany
Erzhausen (1964), 220 MW
Geesthacht (Hamburg) (1958), 120 MW
Goldisthal (2002), 1,060 MW
Happurg (1958), 160 MW
Hohenwarte II (1966), 320 MW
Koepchenwerk (1989), 153 MW
Langenprozelten (1976), 160 MW
Markersbach (1981), 1,050 MW
Niederwartha, Dresden (1958), 120 MW
Waldeck II (1973), 440 MW
India
Bhira, Maharashtra, 150 MW
Kadamparai, Coimbatore, Tamil Nadu, 400 MW (4 x 100 MW)
Nagarjuna Sagar PH, Andhra Pradesh, 810 MW (1 x 110 MW + 7 x 100 MW)
Purulia Pumped Storage Project, Ayodhya Hills, Purulia, West Bengal, 900 MW
Srisailam Left Bank PH, Andhra Pradesh, 900 MW (6 x 150 MW)
Tehri Dam, Uttranchal , 1,000 MW
Iran
Siah Bisheh, Iran (1996), 1,140 MW
Ireland
Turlough Hill (1974), 292 MW
Italy
Chiotas (1981), 1,184 MW
Lago Delio (1971), 1,040 MW
Piastra Edolo (1982), 1,020 MW
Presenzano (1992), 1,000 MW
Japan
Imaichi (1991), 1,050 MW
Kannagawa (2005), 2,700 MW
Kazunogawa (2001), 1,600 MW
Kisenyama, 466 MW
Matanoagawa (1999), 1,200 MW
Midono, 122 MW
Niikappu, 200 MW
Okawachi (1995), 1,280 MW
Okutataragi (1998), 1,932 MW
Okuyoshino, 1,206 MW
Shin-Takasegawa, 1,280 MW
Shiobara, 900 MW
Takami, 200 MW
Tamahara (1986), 1,200 MW
Yagisawa, 240 MW
Yanbaru, Okinawa (1999), 30 MW (First high-head seawater pumped storage in the world) Hitachi
Lithuania
Kruonis Pumped Storage Plant (1993), 900 MW installed, 1,600 MW designed
Luxembourg
Vianden (1964), 1,100 MW
Norway
Note: Norway has many large hydroelectric power stations. At some of the locations listed below, no power is generated: the pumps move water up to reservoirs feeding conventional hydroelectric power stations. [8][9][10]

Aust-Agder
Breive, Bykle
Skarje, Bykle
Hordaland
Aurland III (1979), 270 MW
Jukla, 40 MW
Kastdalen
Nygard, Modalen
Skjeggedal
Møre og Romsdal
Mardal
Monge
Nordland
Tverrvatn
Rogaland
Duge
Hjorteland
Hunnevatn
Saurdal, 640 MW
Stølsdal, 17 MW
Philippines
CBK, 700 MW
Poland
Dychów, 79.5 MW
Niedzica, 92.6 MW
Porabka-Zar, 500 MW
Solina, 200 MW
Zarnowiec, 716 MW
Zydowo, 150 MW
Portugal
Aguieira, 270 MW
Alqueva, 260 MW
Alto Rabagão, 72 MW
Torrão, 144 MW
Vilarinho II, 74 MW
Russia
Kuban (1968), 15.9/19.2 MW
Zagorsk (1994), 1,200/1,320 MW
Zelenchuk (under construction), 140/150.6 MW
Serbia
Bajina Basta (1982), 614 MW
Slovakia [3]
Cierny Váh, 735.16 MW
Liptovská Mara, 198 MW
Ružín, 60 MW
Dobšiná, 24 MW
Slovenia
Avce, 180 MW
South Africa [4]
Drakensberg (1983), 1,000 MW
Palmiet, 400 MW
Steenbras (1979), 180 MW
Ingula (under construction), 1,332 MW
Spain
Aguayo (Cantabria), 339 MW
Aldeadavila (Salamanca), 422 MW (2 X 211 MW) [5]
Moralets-Llauset (Lleida/Huesca), 210 MW [6]
La Muela (Valencia), 628 MW
Sallente-Estany Gento (Lleida), 451 MW [7]
Tajo de la Encantada (Málaga), 360 MW
Tavascan-Montmara (Lleida), 52 MW
Villarino (Salamanca), 810 MW (6 X 135 MW) [8]
Sweden
Juktan, 334 MW [11]
Switzerland
Cleuson-Dixence VS, Lac des Dix, 2,099 MW (turbine)
Guttannen BE / Grimsel 2 (Kraftwerke Oberhasli), Grimselsee, 1070 MW (turbine)
Peccia, Cavergno, Verbano, Bavona, Altstafel, Robiei TI (Maggia Kraftwerke AG), 620 MW (turbine)
Hongrin VD, Lac de l'Hongrin, 240 MW installed, 420 MW planned
Mapragg SG, Stausee Mapragg (Kraftwerke Sarganserland), 370 MW (turbine)
Linthal GL, Linth-Limmern, 340 MW turbine installed; 1000 MW planned pump and turbine by 2015
Altendorf SZ / Einsiedeln, Sihlsee, 340 cubic meters per second
Lobbia GR (EW der Stadt Zürich), 37 MW (pump)
Ova Spin GR (Engadiner Kraftwerke AG), 47 MW (pump)
Ferrera GR, Valle di Lei, 82 MW (pump)
Taiwan
Minghu (1985) 1,000 MW
Mingtan (1994) 1,620 MW
Ukraine
Dniestr HPSP, 972 MW installed, 2,268 MW planned photo
Kaniv HPSP (design stage), 1800 MW [9]
Kyiv HPSP, 235.5 MW [10]
Tashlyk HPSP, 905 MW/-1325 MW [11]
United Kingdom
Ben Cruachan, Scotland (1965), 440 MW (2 × 120 MW + 2 × 100 MW units)
Dinorwig, Wales (1984), 1728 MW (6 × 288 MW units)
Foyers, Scotland (1975), 305 MW
Ffestiniog, Wales (1963), 360 MW (4 × 90 MW units)
United States
California
Castaic Dam (1978), 1,566 MW
Edward C. Hyatt (1968), 780 MW
Helms (1984), 1,200 MW
Iowa Hill, (Proposed 2010), 400 MW [12]
John S. Eastwood (1988), 200 MW
Pyramid Lake (1973), 1,495 MW
San Luis Dam (William R. Gianelli) (1968), 424 MW
Colorado
Cabin Creek (1967), 324 MW
Mount Elbert 200 MW, 1,212 MW
Connecticut
Rocky River (1929), 31 MW
Georgia
Rocky Mountain Pumped Storage Station, 848 MW
Wallace Dam, Lake Oconee/Lake Sinclair, 4 x 52 MW reversible units - operated by Georgia Power
Hawaii
Koko Crater, Oahu, Hawaii (Proposed)
Massachusetts
Bear Swamp (1972), 600 MW
Northfield Mountain (1972), 1,080 MW
Michigan
Ludington (1973), 1,872 MW
Missouri
Clarence Cannon dam (1983), 58 MW (pump-back capability tested twice in 1984 and not used since.[13])
Taum Sauk, 450 MW (pure pump-back; out of operation as of December, 2005)
New Jersey
Mt. Hope, 2,000 MW[12]
Yards Creek Generating Station (1965), 400 MW [14]
New York
Blenheim-Gilboa (1973), 1,200 MW
Lewiston Pump-Generating Plant (Niagara) (1961), 240 MW
Oklahoma
Salina Pumped Storage (Grand River Dam Authority) (1971), 260MW
Pennsylvania
Muddy Run, 1,071 MW
Seneca, 435 MW
South Carolina
Fairfield Pumped Storage (1978), 512MW - fed by Lake Monticello Reservoir
Bad Creek (1991), 1,065 MW - fed by Lake Jocassee
Lake Jocassee (1973), 610 MW
Tennessee
Raccoon Mountain (1978), 1,530 MW
Virginia
Bath County, 2,710 MW (Worlds Largest)[13]
Smith Mountain Lake and Leesville Lake
Washington
Grand Coulee Dam (1981), 314 MW[14]

[edit] References
^ ESA - Pumped Hydro Storage
^ Summary Energy from the Desert - Practical Proposals for Very Large Scale Photovoltaic Power Generation (VLS-PV) Systems
^ http://www.eia.doe.gov/emeu/aer/pdf/pages/sec8_8.pdf
^ http://www.solarnavigator.net/alternative_energy.htm
^ http://www.inference.phy.cam.ac.uk/sustainable/refs/tide/WindPumpedStor.pdf in Renewable and Sustainable Energy Reviews
^ HE Vinodol, HEP Proizvodnja
^ RHE Velebit, HEP Proizvodnja
^ http://www.statkraft.no/pub/vannkraft/Kraftverkene/index.asp]
^ [1]
^ [2]
^ Francisturbinen
^ Mt. Hope: The megawatt line
^ Bath County Pumped Storage Station
^ Grand Coulee Dam

[edit] See also
List of energy topics
Francis turbine
Grid energy storage
Hydroelectricity
Hydropower
Kaplan turbine
Underground power station
Turbine
Water turbine

[edit] External links
Pumped-storage hydroelectricity at the Open Directory Project
Articles about historical mechanical engineering landmarks from ASME:
Rocky River Pumped-storage Hydroelectric Plant (1929)
Hiwassee Dam Unit 2 Reversible Pump-Turbine (1956)
Energy storage using water
[hide]v • d • eElectricity generation

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Technology AC power · Cogeneration · Combined cycle · Cooling tower · Fossil fuel power plant · Induction generator · Micro CHP · Microgeneration · Pumped hydro · Rankine cycle · Virtual power plant

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Categories: Electricity distribution · Electricity economics · Power station technology · Portals: Energy · Sustainable development

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