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.

Intensification, ratio of - The ratio of the secondary pressure to the primary pressure or of the primary flow rate to the secondary flow rate.

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, single shot - An intensifier in which the continuous application of primary fluid at the inlet port can only give a limited volume of secondary 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.

Leakage rate - The rate at which a gas or liquid passes through a barrier. Total leakage rate includes the amounts that diffuse or permeate through the material of the barrier as well as the amount that escapes around it.

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

Line, working - A line which conducts fluid power.

Line - A tube, pipe, or hose for conducting fluid.

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.

Modulus - Tensile stress at a specified elongation. (Usually 100% elongation for elastomers.)

Moving parts logic - The technology of achieving logic control by means of fluid devices having moving parts.

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

Newt - A unit of kinematic viscosity in the English system. It is expressed in square inches per second (see Stokes).

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.

Oil swell - The change in volume of a rubber article due to absorption of oil or other fluid.

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.

Outgassing - A vacuum phenomenon wherein a substance spontaneously releases volatile constituents in the form of vapors or gases. In rubber compounds, these constituents may include water vapor, plasticizers, air, inhibitors, etc.

Output stage - The final stage of hydraulic amplifications used in a servovalve.

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.

Pascal's Law - A pressure applied to a confined fluid at rest is transmitted with equal intensity throughout the fluid.

Permanent set - The deformation remaining after a specimen has been stressed in tension for a definite period and released for a definite period.

Permeability - The rate at which a liquid or gas under pressure passes through a solid material by diffusion and solution. In rubber terminology, it is the rate of gas flow expressed in atmospheric cubic centimeters per second through an elastomeric material one centimeter square and one centimeter thick.

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 - A terminus of a passage in a component to which conductors can be connected.

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).

Power unit - A combination of pump, pump drive, reservoir, controls and conditioning components to supply hydraulic power to a system.

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, atmospheric - Pressure exerted by the atmosphere at any specific location. (Sea level pressure is approximately 14.7 pounds per square inch absolute. 1 bar = 14.5 psi).

Pressure, back - The pressure encountered on the return side of a system.

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, charge - The pressure at which replenishing fluid is formed into a fluid power system.

Pressure, control range - The permissible limits between which system pressure may be set.

Pressure, cracking - The pressure at which a pressure-operated valve begins to pass fluid.

Pressure, differential (pressure drop) - The difference in pressure between any two points of a system or a component.

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, override - The difference between the cracking pressure of a valve and the pressure reached when the valve is passing its rated flow.

Pressure, peak - The maximum pressure encountered in the operation of a component.

Pressure, pilot - The pressure in the pilot circuit.

Pressure, precharge - The pressure of compressed gas in an accumulator prior to the admission of a liquid.

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, shock - The pressure existing in a wave moving at sonic velocity.

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.