Axial Piston - Type of design for hydraulic motors and pumps in which the pistons are arranged parallel with the spindle (input or output shaft).
Axle - A shaft or spindle on which a wheel or pair of wheels revolves.
Bypass Valve - A valve whose primary function is to open a path for the fluid to bypass the motor or pump. Also referred to occasionally as the freewheel valve or dump valve.
Case Drain Line (Return Line) - A line returning fluid from the component housing to the reservoir.
Cavitation - A concentrated gaseous condition within the fluid causing the rapid implosion of a gaseous bubble.
Center Section - A device which acts as the valve body and manifold of the transmission.
Charge - To replenish a hydraulic system faster than what normal atmospheric pressure can accomplish.
Charge Pump - A device which supplies replenishing fluid to the fluid power system (closed loop).
Charge Pressure - The pressure at which replenishing fluid is forced into a fluid power system.
Charge Relief Valve - A pressure control valve whose primary function is to limit pressure in the charge circuit.
Check Valve - A valve whose primary function is to restrict flow in one direction.
Closed Loop - A sealed and uninterrupted circulating path for fluid flow from the pump to the motor and back.
Decay Rate - The ratio of pressure decay over time.
Displacement - The quantity of fluid that can pass through a pump or motor in a single revolution.
End Cap - See "Center Section."
Entrained Air - A mechanically generated mixture of air bubbles having a tendency to separate from the liquid phase.
Flow - To move or proceed steadily (fluid); pump creates flow (expressed in gallons per minute - GPM).
Gerotor - A formed rotor set operating about an eccentric that provides a fixed displacement for pumps or motors.
Hydraulic Motor - A device which converts hydraulic fluid power into mechanical force and motion by transfer of flow under pressure.
Hydraulic Pump - A device which converts mechanical force and motion into hydraulic fluid power by producing flow.
Hydraulics - Engineering science pertaining to liquid pressure and flow.
Hydrostatic Pump - See "Hydraulic Pump."
Hydrostatic Transaxle - A multi component assembly including a gear case and a hydrostatic transmission.
Hydrostatic Transmission - The combination of a hydraulic pump and motor in one housing to form a device for the control and transfer of power.
Hydrostatics - Engineering science pertaining to the energy of confined fluids.
Inlet Line - A supply line to the pump.
Integrated Zero-Turn Transaxle - The combination of a hydrostatic transmission and gear case in one housing to form a complete transaxle.
Manifold - A conductor which provides multiple connection ports.
Neutral - Typically described as a condition in which fluid flow and system pressure is below that which is required to turn the output shaft of the motor.
Pressure - Application of steady force by one body in contact with another; caused by resistance to flow; normally expressed in pounds per square inch (PSI).
Pressure Decay - A falling pressure.
Priming - The filling of the charge circuit and closed loop of the fluid power system during start up, frequently achieved by pressurizing the fluid in the inlet line.
Purging - The act of replacing air with fluid in a fluid power system by forcing fluid into all of the components and allowing the air a path of escape.
Rated Flow - The maximum flow that the power supply system is capable of maintaining at a specific operating pressure.
Relief Valve - A pressure operated valve which by-passes pump delivery (flow), limiting system pressure to a predetermined maximum value.
Scoring - Scratches in the direction of motion of mechanical parts caused by abrasive contaminants.
Swash Plate - A mechanical device used to control the displacement of the pump pistons in a fluid power system.
System Charge Check Valve - A valve controlling the replenishing flow of fluid from a charge circuit to the closed loop in a fluid power system.
System Pressure - The pressure which overcomes the total resistance in a system, including all efficiency losses.
Valve - A device which controls fluid flow direction, pressure, or flow rate.
Variable Displacement Pump - A pump in which the displacement per revolution can be varied.
Volumetric Displacement - The volume for one revolution.