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Glossary of Terms - All Terms

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Glossary Subsets


Pounds per square inch absolute.


Not in series but fed from the same sources.


A unit of pressure in metric system, usually expressed in kPa (kilopascals).
• 1 kPa = 0.01 bar = 0.145 psi.


A fluid conducting path which lies within or passes through a component.

Peel Strength

The peeling force necessary to break a bond, divided by its cross-sectional area.


The entering of an adhesive into a substrate.

Pilot Pressure

Auxiliary pressure used to actuate or control hydraulic components.

Pilot Valve

An auxiliary valve to control the operation of another valve.


A cylindrically shaped part with only one diameter that is used to transmit thrust. A ram.


A cylindrically shaped part which fits within a cylinder and transmits or receives motion by means of a connecting rod.


Often shown as p, it is the ratio of circumference of circle to diameter. Numerically can be expressed as 22/7 or 3.14159265 more accurately.


The portion of a cage shaped to hold the ball or roller.


The magnetic poles in an electric motor that result from connection and placement of the windings in the motor. 7,200 divided by the number of poles gives the synchronous speed of the motor, i.e., a 4-pole motor is 1,800 rpm (7200/4).


A chemical reaction where two or more small molecules continue to form larger molecules that contain repeating structural units of the original molecules.


A chemical compound or mixture of componds formed by polymerization.


That part of certain valves which prevents flow when it closes against a seat.


An internal or external passage in a component.

Positive Displacement

A characteristic of a pump or motor which has the inlet positively sealed from the outlet so that fluid cannot re-circulate in the pump or motor.

Pot Life

The period of time an adhesive or potting compound remains useful after adding an accelerator, catalyst or exposure to other curing conditions.

Potential Energy

The energy level change which results when an object is raised to a new height.


Enclosing an article in an envelope of adhesive.

Pour Point

The lowest rated temperature at which a hydraulic fluid will flow.


A control element in the servo-system which measures and controls electrical potential.

Power Factor

The ratio of real power actually used to the amount of apparent power being supplied to an electrical load.


Work per unit of time, measured in horsepower (hp) or watts.

PPM (Pars Per Million)

Unit of mearsure representing the number of particles in a given body.

Power Relay

An electro-mechanical device that allows automatic or remote operation to repeatedly establish or interrupt an electrical power circuit. Sometimes called a contactor.

Precharge Pressure

The pressure of compressed gas in an accumulator prior to the admission of liquid.


An internal loading characteristic in a bearing which is independent of any external radial and/or axial load carried by the bearing.

Prelubricated Bearing

A shielded, sealed, or open bearing originally lubricated by the manufacturer.


Force per unit area; usually expressed in psi, bar, or kPa.

Pressure Differential

Same as pressure drop. The change in pressure between two points in a system, usually referring to the inlet and outlet ports of a component. Also expressed as DP (Delta P).

Pressure Override

The difference between the cracking pressure and the full flow pressure of a valve.

Pressure Drop

The change in pressure between two points in a system, usually referring to the inlet and outlet ports of a component. Also expressed as DP (Delta P).

Pressure Line

The line carrying the fluid from the pump outlet to the pressurized port of the actuator.

Pressure Reducing Valve

A valve which limits the maximum pressure at its outlet regardless of the inlet pressure.


A coating applied to a surface prior to the application of an adhesive in order to enhance the strength of the bond or speed up the cure.

PSIG (Gauge Pressure)

A pressure scale which ignores atmospheric pressure, i.e., its zero point is atmospheric pressure (14.7 psia at sea level).

PSIA (Pounds Per Square Inch Absolute)

See Absolute Pressure


A device which converts mechanical force and motion into hydraulic fluid flow.