PRIME MOVER—The source of mechanicalpower used to drive the pump or compressor.PUMP—A device that converts mechanicalforce and motion into hydraulic fluid power.PUMP, AXIAL PISTON—A pump havingmultiple pistons disposed with their axes parallel.PUMP, CENTRIFUGAL—A pump thatproduces fluid velocity and converts it to pressurehead.PUMP, FIXED-DISPLACEMENT—Apump in which the displacement per cycle cannotbe varied.PUMP, RADIAL PISTON—A pump havingmultiple pistons disposed radially actuated by aneccentric element.PUMP, VARIABLE-DISPLACEMENT—Apump in which the volume of fluid per cycle canbe varied.RANKINE SCALE—A thermometer scalebased on absolute zero of the Fahrenheit scale,in which the freezing point of water isapproximately 492°R.RATIO—The value obtained by dividing onenumber by another, indicating their relativeproportions.RECEIVER—A container in which gas isstored under pressure as a supply source forpneumatic power.RECIPROCATING—Moving back andforth, as a piston reciprocating in a cylinde.,RESERVOIR—A container for storage ofliquid in a fluid power system.RESPONSE TIME—The time lag between asignal input and the resulting change of output.RESTRICTOR—A device that reduces thecross-sectional flow area.RESTRICTOR, ORIFICE—A restrictor, thelength of which is relatively small with respect toits cross-sectional area. The orifice may be fixedor variable. Variable types are noncompensated,pressure compensated, or pressure and tempera-ture compensated.RETURN LINE—A line used for returningfluid back into the reservoir or atmosphere.SEPARATOR—A device whose primaryfunction is to isolate undesirable fluids and orcontaminants by physical properties other thansize.SERVO—A device used to convert a smallmovement into a greater movement of force.SOLID—The form of matter that has adefinite shape and a definite volume.SPECIFIC GRAVITY—The ratio of theweight of a given volume of a substance to theweight of an equal volume of some standardsubstance.STEADY FLOW—A flow in which thevelocity, pressure, and temperature at any pointin the fluid do not vary with time.STRAINER—A coarse filter.STOKE—The standard unit of kinematicviscosity in the cgs system. It is expressed in squarecentimeters per second; 1 centistoke equals 0.01stoke.STUFFING BOX—A cavity and closure withmanual adjustment for a sealing device.SUPPLY LINE—A line that conveys fluidfrom the reservoir to the pump.SURGE—A momentary rise of pressure in acircuit.SYNCHRONIZE—To make two or moreevents or operations occur at the proper time withrespect to each other.SYNTHETIC MATERIAL—A complexchemical compound that is artificially formed bythe combining of two or more simpler compoundsor elements.TANK—A container for the storage of fluidin a fluid power system.THEORY—A scientific explanation, tested byobservations and experiments.THERMAL EXPANSION—The increase involume of a substance due to temperature change.A4-7
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