Pump - A device which converts mechanical torque and motion into hydraulic fluid power.

Pump, fixed displacement - A hydraulic pump in which the volume displaced per cycle cannot be varied.

Pump, gear, external - Pump with two or more external gears.

Pump, gear, internal - Pump with an internal gear in engagement with one or more external gears.

Pump, gear - Pump in which two or more gears act in engagement as pumping members.

Pump, hydraulic - A device which converts mechanical force and motion into hydraulic fluid power.

Pump, multiple stage - Two or more hydraulic pumps in series.

Pump, piston, axial - Pump having several pistons with mutually parallel axes which are arranged around and parallel to a common axis.

Pump, piston, inline - Pump having several pistons with mutually parallel axes arranged on a common plane.

Pump, piston, radial - Pump having several pistons arranged to operate radially.

Pump, piston - Pump in which the fluid volume is displaced by one or more reciprocating pistons.

Pump, screw - A hydraulic pump having one or more screws rotating in a housing.

Pump, vane, balanced - Pump in which the transverse forces on the rotor are balanced.

Pump, vane, unbalanced - Pump in which the transverse forces on the rotor are not balanced.

Pump, vane - A hydraulic pump having multiple radial vanes within a supporting rotor.

Pump, variable displacement - A hydraulic pump in which the volume displaced per cycle can be varied.

Quick -Acting Coupling - A component that can quickly join or separate a fluid line repeatedly by hand without the use of tools.

Refrigerated Dryer - Moisture is separated by lowering the air temperature by means of refrigeration compressor and heat exchanger.

Regenerative Circuit - A circuit in which pressurized fluid discharged from a component is returned to the system to reduce power input requirements.

Regenerative Dryer - The capacity of the dryer to separate moisture can be restored without replacing the drying compound.

Regulator, Air  Pressure - A (usually adjustable) pressure-reducing valve with pressure gauge that transforms a fluctuating air pressure supply to provide a constant, lower pressure output.

Reinforcing Agent - Material dispersed in an elastomer to improve compression, shear, or other stress properties.

Reservoir (tank) - A container for storage of liquid in a fluid power system.

Reservoir, Hydraulic - A reservoir for storing and conditioning a liquid in a hydraulic system.

Reservoir, pressure sealed - A sealed reservoir for storage of fluids under pressure.

Resilient - Capable of returning to original size and shape after deformation.

Reyn - The standard unit of absolute viscosity in the English system. It is expressed in pound-seconds per square inch.

Reynolds Number - A numerical ratio of the dynamic forces of mass flow to the shear stress due to viscosity. Flow usually changes from laminar to turbulent between Reynolds Numbers 2,000 and 4,000.

Ring, O - An elastomeric circular seal that has a round cross section.

Ring, piston - A piston sealing ring. It is usually one of a series and is often split to facilitate expansion or contraction.

Ring, scraper - A ring which removes material by a scraping action.

Rotation - The direction of rotation is always quoted as viewed looking at the shaft end. In dubious cases, provide a sketch.