Terminology

• Accumulator – A container which stores fluids under pressure as a source of hydraulic power. It may also be used as a shock absorber.
• Actuator – A mechanical device for moving or controlling a load; a cylinder or motor, for example.
  Area – The total amount of surface on a flat plane. Usually measured in square inches.
• Bleed – The process by which air is removed from a hydraulic system.
• Bypass – A secondary passage for fluid flow.
• Cam Lobe Motor – A hydraulic radial piston motor in which rotational force is created by the outward movement of the pistons against the lobes of a stationary cam.
• Cavitation – A phenomenon which occurs when the pressure at a point in a hydraulic system is lowered below the vapor pressure of the oil in the system. This allows bubbles of oil vapor to form in the oil. If this occurs at the pump inlet, the quick pressure rise inside the pump forces these bubbles to collapse violently. This can cause erosion of metal parts, noise and vibration.
• Circuit – A series of component parts connected to each other by fluid lines or passages. Usually part of a “system”.
• Closed Center System – A hydraulic system in which the control valves are closed during neutral, stopping oil flow. Flow in this system is varied, but pressure remains constant.
• Controller – A microprocessor that controls electro-hydraulic valve functions.
• Cooler (Oil) – A heat exchanger which removes heat from a fluid. (See “Heat Exchanger.”)
• Coupler – A device to connect two hoses or lines, or to connect hoses to valve receptacles.
• Cusion – A device sometimes built into the end of a cylinder which restricts outlet flow and thereby slows down the piston.
• Cycle – A single complete operation of a compo- nent which begins and ends in a neutral position.
• Cylinder – A device for converting fluid power into linear or circular motion. An “actuator”. Basic design types include piston and vane units.
  • Double-Acting Cylinder – A cylinder in which fluid force can be applied to the movable element in either direction.
  • Piston- Type Cylinders – A cylinder which uses a sliding piston in a housing to produce straight movement.
  • Rotary Cylinders – A cylinder in which fluid force is applied to produce circular motion. Single-Acting Cylinder-A cylinder in which fluid force can be applied to the movable element in only one direction.
  • Vane-Type Cylinder – A cylinder which uses a turn- ing vane in a circular housing to produce rotary movement.
• Force – The measured amount of pressure applied to a given area. The weight of the load (pushing or pulling).
• Flow – The movement of oil in a circuit from high-pressure to low-pressure along the path of least resistance.
• GPM – Gallons Per Minute. A measure of fluid flow.
• Power – The measure of the rate at which work is done over time. Usually expressed in Horsepower or Watts.
• Pressure – A measure of force on a unit of area. Measured in pounds per square inch (PSI).
• Pressure Drop – The difference in pressure between two points in a system. Pressure is lower downstream.