Fluid power

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.

Practical use

A fluid power system has a pump driven by a prime mover (such as an electric motor or internal combustion engine) that converts mechanical energy into fluid energy, eventually using a set of control valves and dedicated circuit architecture. 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.

Application

• 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 increased 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 to a working pressure of up to around 100 psi (7 bar).

See also

• Hydraulic circuit
• Hydraulic machinery
• Hydraulic power network
• London Hydraulic Power Company
• Pneumatic circuit
• Pneumatic actuator

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