Fluid power is the use of fluids under pressure to generate, control, and transmit power. Fluid power is subdivided into hydraulics using a liquid such as mineral oil or water, and pneumatics using a gas such as air or other gases. Compressed-air and water-pressure systems were once used to transmit power from a central source to industrial users over extended geographic areas; fluid power systems today are usually within a single building or mobile machine.
A fluid power system has a pump driven by a prime mover (such as an electric motor or IC engine) that converts mechanical energy into fluid energy. This fluid flow is used to actuate a device such as:
- A Hydraulic cylinder or Pneumatic cylinder, provides force in a linear fashion
- A Hydraulic motor or Pneumatic motor, provides continuous rotational motion or torque
- A Rotary actuator provides rotational motion of less than 360 degrees.
The choice of liquid or gas as the fluid power medium is governed by the application requirements:
- Cost: pneumatics are considerably less expensive to build and operate. For one, air is used as the compressed medium, so there is no need to provide means to drain or recover fluid. With increasing working pressures, Hydraulics require larger parts than pneumatics.
- Precision: Unlike liquids, gases change volume significantly when pressurized making it difficult to achieve precision.
- Safety: Compressed gases tend to expand at high velocities when decompressed, thus pneumatics are typically limited in utilities with a working pressure up to around 100 psi (7 bar).
- Hydraulic circuit
- Hydraulic power network
- London Hydraulic Power Company
- Pneumatic circuit
- Pneumatic actuator
- 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
- Hydraulicweb with animations; English and Spanish
- National Fluid Power Association
- Using Equivalent Lengths of Valves and Fittings
- Fluid Power Net International, a scientific association in the field of fluid power
- International Fluid Power Society
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