Hydraulic power is power transmitted by controlled circulations of fluid under pressure to a motor that converts it to mechanical output capable of doing work. Hydraulic power systems tend to have more flexibility than electrical and mechanical systems. Hydraulic systems also produce more power than other equally sized systems.
There are numerous applications for hydraulic power. Hydraulic power systems provide accurate and rapid response to controls. This is one of the features that makes hydraulic power systems widely employed in many industries, including the aircraft and automobile industries, construction as well as heavy machinery industries.
A reservoir, hydraulic pump, valves and actuators are the main parts of any hydraulic system. There are several different types of hydraulic pumps including gear pumps, vane pumps, axial piston pumps, radial piston pumps and gerotor pumps. Gear and vane pumps are simple and cheap, axial piston pumps allow varying output flow for automatic pressure output. Gerotor pumps are an efficient medium-pressure pump, radial piston pumps are used for high-pressure, low-flow applications.
There are two basic types of motors used in hydraulic power systems: linear and rotational motors. Linear motors are used when high force, straight line motion is needed. Brake cylinders in automobiles and control actuators in aircraft use linear motors. Digging equipment, printing presses as well as spindle drives all use hydraulic rotational motors. The application will usually dictate which type of motor will be employed in the hydraulic device.
Hydraulic pumps utilize hydraulic power to produce high amounts of pressure in pounds per square inch (psi). Pressure is also measured in "bars" in which one bar is equal to 100,000 newtons per square meter. Certain hydraulic pumps are suitable for working in certain pressure ranges. The gear pump and vane pump for example, are ideal for producing pressures under 3,000 psi, or 200 bars. Radial piston pumps are capable of producing pressures up to 650 bars.