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Cartridge: The replaceable element of a fluid filter, The pumping unit from a vane pump, composed rotor, ring, vanes and one or both side plates.

Cartridge Valve: A valve that is inserted into a standard size cavity in a manifold block and is held in place with either self contained screw threads or a cover secured with bolts. May be slip in or screw in types. Perform directional, pressure or flow control functions.

Cavitation: A localised gaseous condition within a liquid stream which occurs where the pressure is reduced to the vapor pressure.

Chamber: A compartment within a hydraulic unit. May contain elements to aid in operation or control of a unit.

Charge: To replenish a hydraulic system above atmospheric pressure. To fill an accumulator with fluid under pressure.

Charge Pressure: The pressure at which replenishing fluid is forced into hydraulic system.

Check Valve: A valve which permits flow of fluid in one direction only.

Choke: A restriction, the length of which is large with respect to its cross section dimension.

Circuit: An arrangement of components interconnected to perform a specific function within system.

Closed Center Valve: One in which all ports are blocked in the center or neutral positions.

Closed Center Circuit: One in which flow through the system is blocked in neutral and pressure at the pump outlet is maintained at the maximum pressure control setting.

Commutation: The switching sequence of drive voltage into motor phase windings necessary to assure continuos motor rotation. A brushed motor relies upon brush/bar contact to mechanically switch the windings. A brushless motor requires a device that senses rotor rotational position feds that information to a drive that determines the next switching sequence.

Closed Loop: A broadly applied term relating to any system where the output is measured and compared to the input. The output is then adjusted to reach the desired condition. In motion control, the term describes a system wherein a velocity or position (or both) transducers is used to generate correction signals by comparison to desired parameters.

Command Signal: An external signal variable pumps and motors which alters displacements when system pressure exceeds its adjusted pressure settings.

Component: A single hydraulic or electric unit.

Compressibility: The change in volume of a unit volume of fluid when subjected to a unit change in pressure.

Cooler: A heat exchanger used to remove heat from the hydraulic fluid.

Counterbalance valve: A pressure control valve which maintains backpressure to prevent a load from falling.

Critical Damping: A system is critically damped when the response to a step change in desired velocity or position is achieved in the minimum possible time with little or no overshoot.

Crossover Frequency: The frequency at which the gain intercepts the 0db point on a Bode plot (used in reference to the open-loop gain plot).

Cushion: A device sometimes built into the ends of a hydraulic cylinder which restricts the flow of fluid at the outlet port, thereby arresting the motion of the piston rod.

Cylinder: A device which converts fluid power into linear mechanical force and motion. It usually consists of a movable element such as a piston rod, plunger rod, plunger or ram, operating within a cylindrical bore.