NEUTRALIZATION NUMBERA mea-sure of the total acidity or basicity of an oil; this includes organic or inorganic acids or bases or a combination of them.

OXIDATIONThe process by which oxygen unites with some other substance, causing rust or corrosion.

PACKINGA class of seal that is used to provide a seal between two parts of a unit which move in relation to each other.

PASCALS LAWA pressure applied to a confined fluid at rest is transmitted with equal intensity throughout the fluid.

PERIPHERYThe outside surface, espe-cially that of a rounded object or body.

PIPEA type of fluid line whose dimensions are designated by nominal (approximate) inside diameter and wall thickness.

PNEUMATICSEngineering science per-taining to gaseous pressure and flow.

PORTAn internal or external terminus of a passage in a component.

POTENTIAL ENERGYThe energy a sub-stance has because of its position, its condition, or its chemical composition.

POUR POINTThe lowest temperature at which a liquid will flow under specified con-ditions.

POWER UNITA combination of pump, pump drive, reservoir, controls, and conditioning components which may be required for its application.

POWERThe rate of doing work or the rate of expanding energy.

PRESSUREThe amount of force distrib-uted over each unit of area, usually expressed in pounds per square inch.

PRESSURE, ABSOLUTEThe sum of atmospheric and gauge pressures.

PRESSURE, ATMOSPHERICPressure exerted by the atmosphere at any specific location.

PRESSURE, BACKThe pressure encoun-tered on the return side of a system.

PRESSURE, DIFFERENTIALThe dif-ference in pressure between any two points of a system or a component.

PRESSURE, HEADThe pressure due to the height of a column or body of fluid. It is usually expressed in feet.

PRESSURE, OPERATINGThe pressure at which a system operates.

PRESSURE, PRECHARGEThe pressure of compressed gas in an accumulator prior to the admission of a liquid.

PRESSURE, PROOFThe nondestructive test pressure in excess of the maximum rated operating pressure.

PRESSURE, STATICThe pressure in a fluid at rest.

PRESSURE SWITCHAn electrical switch operated by the increase or decrease of fluid pressure.

PRIME MOVERThe source of mechanical power used to drive the pump or compressor.

PUMPA device that converts mechanical force and motion into hydraulic fluid power.

PUMP, AXIAL PISTONA pump having multiple pistons disposed with their axes parallel.

PUMP, CENTRIFUGALA pump that produces fluid velocity and converts it to pressure head.

PUMP, FIXED-DISPLACEMENTA pump in which the displacement per cycle cannot be varied.

PUMP, RADIAL PISTONA pump having multiple pistons disposed radially actuated by an eccentric element.

PUMP, VARIABLE-DISPLACEMENTA pump in which the volume of fluid per cycle can be varied.

RANKINE SCALEA thermometer scale based on absolute zero of the Fahrenheit scale, in which the freezing point of water is approximately 492R.

RATIOThe value obtained by dividing one number by another, indicating their relative proportions.

RECEIVERA container in which gas is stored under pressure as a supply source for pneumatic power.

RECIPROCATINGMoving back and forth, as a piston reciprocating in a cylinde.,

RESERVOIRA container for storage of liquid in a fluid power system.

RESPONSE TIMEThe time lag between a signal input and the resulting change of output.

RESTRICTORA device that reduces the cross-sectional flow area.

RESTRICTOR, ORIFICEA restrictor, the length of which is relatively small with respect to its cross-sectional area. The orifice may be fixed or variable. Variable types are noncompensated, pressure compensated, or pressure and tempera-ture compensated.

RETURN LINEA line used for returning fluid back into the reservoir or atmosphere.

SEPARATORA device whose primary function is to isolate undesirable fluids and or contaminants by physical properties other than size.

SERVOA device used to convert a small movement into a greater movement of force.

SOLIDThe form of matter that has a definite shape and a definite volume.

SPECIFIC GRAVITYThe ratio of the weight of a given volume of a substance to the weight of an equal volume of some standard substance.

STEADY FLOWA flow in which the velocity, pressure, and temperature at any point in the fluid do not vary with time.

STOKEThe standard unit of kinematic viscosity in the cgs system. It is expressed in square centimeters per second; 1 centistoke equals 0.01 stoke.

STUFFING BOXA cavity and closure with manual adjustment for a sealing device.

SUPPLY LINEA line that conveys fluid from the reservoir to the pump.

SURGEA momentary rise of pressure in a circuit.

SYNCHRONIZETo make two or more events or operations occur at the proper time with respect to each other.

SYNTHETIC MATERIALA complex chemical compound that is artificially formed by the combining of two or more simpler compounds or elements.

TANKA container for the storage of fluid in a fluid power system.

THEORYA scientific explanation, tested by observations and experiments.

THERMAL EXPANSIONThe increase in volume of a substance due to temperature change.

TORQUEA force or combination of forces that produces or tends to produce a twisting or rotary motion.

TUBINGA type of fluid line whose dimensions are designated by actual measured outside diameter and by actual measured wall thickness.

TURBINEA rotary motor actuated by the reaction, impulse, or both, of a flow of pressurized fluid.

VALVEA device that controls fluid flow direction, pressure, or flow rate.

VALVE, CHECKA directional control valve that permits flow of fluid in only one direction.

VALVE, COUNTERBALANCEA pressure control valve that maintains back pressure to prevent a load from falling.

VALVE, DIRECTIONAL CONTROLA valve whose primary function is to direct or prevent flow through selected passages.

VALVE, FLOW CONTROLA valve whose primary function is to control flow rate.

VALVE, HYDRAULICA valve for con-trolling liquid.

VALVE, PILOTA valve used to operate another valve or control.

VALVE, PNEUMATICA valve for con-trolling gas.

VALVE, PRESSURE REDUCINGA pressure control valve whose primary function is to limit outlet pressure.

VALVE, PRIORITYA valve that directs flow to one operating circuit at a fixed rate and directs excess flow to another operating circuit.

VALVE, RELIEFA pressure control valve whose primary function is to limit system pressure.

VALVE, SELECTORA directional control valve whose primary function is to selectively interconnect two or more ports.

VALVE, SEQUENCEA valve whose primary function is to direct flow in a pre-determined sequence.

VALVE, SERVOA directional control valve that modulates flow or pressure as a function of its input signal.

VALVE, SHUTOFFA valve that operates fully open or fully closed.

VALVE, UNLOADINGA pressure control valve whose primary function is to permit a pump or compressor to operate at minimum load.

VELOCITYThe rate of motion in a particular direction. The velocity of fluids is usually expressed in feet per second.

VENTURIA tube having a narrowing throat or constriction to increase the velocity of fluid flowing through it. The flow through the venturi causes a pressure drop in the smallest section, the amount being a function of the velocity of flow.

VISCOSITYA measure of the internal friction or resistance of a fluid to flow.

VISCOSITY INDEXA measure of the viscosity-temperature characteristics of a fluid as referred to that of two arbitrary reference fluids.

SECONDS (SUS)The time in seconds for 60 milliliters of oil to flow through a standard orifice at a given temperature.

VISCOSITY, KINEMATICThe absolute viscosity divided by the density of the fluid. It is usually expressed in centistokes.

VOLUME OF FLOWThe quantity of fluid that passes a certain point in a unit of time. The volume of flow is usually expressed in gallons per minute for liquids and cubic feet per minute for gases.

WORKThe transference of energy from one body or system to another. That which is accomplished by a force acting through a distance.