Indicator, differential pressure - An indicator which signals a difference in pressure between two points in a fluid power system.

Inhibitor - Any substance which, when present in very small proportions, slows, prevents or modifies chemical reactions such as corrosion or oxidation.


Intensifier, double acting - A unit which magnifies the secondary fluid pressure regardless of the direction of flow of the primary fluid.

Intensifier, single acting - A unit which only magnifies the fluid pressure in one direction of flow of the primary fluid.


Intensifier - A device which converts low pressure fluid power into higher pressure fluid power.

Joint - A line positioning connector.

Joint, rotary - A joint connecting lines which have relative operational rotation.


Line, return - A pipe (conductor) to return the working fluid to the reservoir.

Line, working - A line which conducts fluid power.


Lubricator - A device which adds controlled or metered amounts of lubricants into a fluid power system.

Magnetic plug - A plug which attracts and holds ferromagnetic particles.

Manifold - A conductor which provides multiple connection ports.

Maximum inlet pressure - The maximum rated gage pressure applied to the inlet port of the regulator.

Memory - Tendency of a material to return to original shape after deformation.

Meter-in Circuit  - A speed control circuit in which the control is achieved by regulating the supply flow to the actuator.

Meter-out Circuit - A speed control circuit in which the control is achieved by regulating the exhaust flow from the actuator.

Modulus of elasticity - One of the several measurements of stiffness or resistance to deformation, but often incorrectly used to indicate specifically static tension modulus.



Muffler - A device for reducing gas flow noise. Noise is decreased by back pressure control of gas expansion.


NOR device - A control devices which has its output in the logical 1 state if and only if all the control signals assume the logical 0 state.

NOT device - A control device which has its output in the logical 1 state if and only if the control signal assumes the logical 0 state. The NOT device is a single input NOR device.


Open Circuit - A circuit in which return fluid is directed to a reservoir before being recirculated.

OR device - A control device which has its output in the logical 0 state if and only if all the control signals assume the logical 0 state.



Ozone resistance - Ability to withstand the deteriorating effect of ozone (which generally causes cracking).

Packing — Pressure, System

Packing - A sealing device consisting of bulk deformable material of one or more mating deformable elements, reshaped by manually adjustable compression to obtain and maintain effectiveness. It usually uses axial compression to obtain radial sealing.




Petroleum fluid - A fluid composed of petroleum oil which may contain additives and/or inhibitors.

Pipe - A conductor whose outside diameter is standardized for threading. Pipe is available in standard, extra strong, or double extra strong wall thickness.

Piston rod - The element transmitting mechanical force and motion from the piston.

Plasticizer - A substance, usually a heavy liquid, added to an elastomer to decrease stiffness, improve low temperature properties, and improve processing.

Pneumatics - Engineering science pertaining to gaseous pressure and flow.

Poise - The standard unit of dynamic viscosity in the cgs (centimeter gram second) system. It is the ratio of the shearing stress to the shear rate of fluid and is expressed in milli-pascal sec. (equals 1 centipoise).

Polymer - A material formed by the joining together of many (poly) individual units (mer) of one or more monomers; synonymous with elastomers.


Port, differential pressure - A port which provides a passage to the upstream and downstream sides of a component.

Post cure - The second step in the vulcanization process for the more exotic elastomers. Provides stabilization of parts and drives off decomposition products resulting from the vulcanization process.

Pour point - The lowest temperature at which a liquid will flow under specified conditions (ASTM Designation D97).


Pressure - Force per unit area, usually expressed in pounds per square inch (bar).

Pressure, absolute - The pressure above zero absolute, i.e., the sum of atmospheric and gage pressure. In vacuum related work it is usually expressed in millimeters of mercury (mm-Hg).



Pressure, breakloose (breakout) - The minimum pressure which initiates movement.

Pressure, burst - The pressure which causes failure of and consequential loss of fluid through the product envelope.





Pressure, gage - Pressure differential above or below ambient atmospheric pressure.

Pressure, induced - Pressure generated by an externally applied force.

Pressure, inlet - The pressure at the apparatus inlet port.

Pressure, intensified - In a fluid power cylinder, the outlet pressure required to slow the piston rod extending under regulated pressure introduced at the cap end.

Pressure, maximum inlet - The maximum rated gage pressure applied to the inlet.

Pressure, nominal - A pressure valve assigned to a component or system for the purpose of convenient designation.

Pressure, outlet - Pressure at the apparatus outlet port.



Pressure, pilot - The pressure in the pilot circuit.


Pressure, proof - The non-destructive test pressure, in excess of the maximum rated operating pressure, which causes no permanent deformation, excessive external leakage, or other resulting malfunction.

Pressure, rated - The qualified operating pressure which is recommended for a component or system by the manufacturer.


Pressure, static - The pressure in a fluid at rest.

Pressure, surge - The pressure resulting from surge conditions.

Pressure, system - The pressure which overcomes the total resistances in a system. It includes all losses as well as useful work.