Glossary and index of fluid power principles and components P
A seal or gasket. See SEAL, O-RING and GASKET
PARALLEL DATA TRANSMISSION
A form of digital data transmission in which all of the bits of a binary word are processed or transmitted at the same time. Faster than serial transmission but requires separate circuitry for each bit.
A piece of debris (sand, dirt, metal, fabric, etc.) Found in a fluid.
The visual or electronic summation of the quantity of particles, grouped by size, in a fluid sample of specified size.
A hole through which fluid is passed in a fluid power system. See TUBE, PIPE, HOSE and MANIFOLD.
The process of migration of a substance into and through another usually the movement of gas into and through a hose material; the rate of permeation is specific to the substance, temperature, pressure, and the material being permeated.
A hydraulic oil (fluid) that is made from a petroleum base. Normally will support combustion if heated to a specific temperature.
A term used to describe the quantity of cyclic electrical power sources in a high voltage system. Most commonly 1phase or 3-phase.
A time difference between the input and output signal of a control unit or system, usually measures in degrees.
PHOSPHATE ESTER FLUID
A hydraulic oil (fluid) that is made from an ester base. A synthetic fluid, manufactured to specific characteristics. Normally will not support combustion if heated to a specific temperature.
A passage in a fluid power system that is used to transport a fluid at a pressure lower than the normal operating pressure to facilitate controlled shifting of spool valves.
PILOT-OPERATED CHECK VALVE
A special check valve that may be opened against a check load by applying pilot pressure from a secondary source to open the check to free reverse flow.
The pressure in the pilot circuit.
A valve applied to operate another valve or control. The controlling stage of a 2stage valve.
A passage in a fluid power system that is constructed of metal and conforms dimensionally to standard established by the ANSI. May be acquired by size and schedule, where increase in wall thickness does not increase the outside diameter. See TUBE.
A cylindrically shaped part in which fits within a cylinder
A cylinder in which the movable element has a greater cross-sectional area than the piston rod.
A metal ring that is used to seal high pressure fluid inside a passage to prevent (limit) leakage across the passage. Normally found in cylinders.
1) The distance from one point on a helix to the corresponding point on the next turn of the helix, measured parallel to the axis. 2) The distance between the two peaks of adjacent corrugation or convolution.
An individual group of reinforcing braid wires or strands.
A material, usually metal applied to another metal by electroplating for the purpose of reducing corrosion; typically a more noble metal such as zinc is applied to steel.
A cylinder in which the movable element has the same cross-sectional area as the piston rod.
A macromolecular material formed by the chemical combination of monomers, having either the same or different chemical compositions.
That part of certain valves which blocks flow when it closes against a seat.
An internal or external terminus of a passage in a component.
A characteristic of a pump or motor when a constant volume is delivered for each revolution or stroke.
An electrical device that changes its internal resistance when moved to a specified point. Most commonly found in electronic control panels. Used to change the voltage in a control system for required control changes (position, speed, pressure, etc.)
POUNDS PER SQ. INCH, GAUGE (PSIG) & ABSOLUTE (PSIA)
The measure of pressure, corrected for atmospheric pressure, that is `zero' psig= 14.65 psia. `Zero' psia = absolute zero vacuum.
Work per unit of time measured in horsepower (hp) or watts (W).
An integral power supply unit usually containing a pump, reservoir, relief valve and directional control.
Term used to describe a fluid power source. A hydraulic power unit.
A valve that is arranged so its inlet port is connected to a reservoir or tank and so that fluid will flow from the inlet of the valve into a cylinder or ram when opened. When closed, the valve must close off the ram or cylinder from the reservoir or tank to permit application of high pressure from another source on the cylinder side of the valve. Most commonly used to fill large rams on presses to take up non-operating stroke.
The pressure of compressed gas in an accumulator prior to the admission of liquid.
Force per unit area. Usually expressed in pounds per square inch (psi), bar or kilopascal (kPa).
A hydro-mechanical device fitted to a pump or other flow producing/controlling device that reduces flow when pressure rises and increases flow as pressure decreases, to preset limits.
PRESSURE DIFFERENTIAL (Drop)
The difference in pressure between any two points in a system or a component.
PRESSURE DIFFERENTIAL SWITCH
A digital device that opens or closes a switch when the internal pressure differential changes state. Most commonly used to sense clogging of filter elements.
See Pressure, Differential.
A visual indicator of pressure that is set for `zero' psi at atmospheric pressure and includes a dial which will continue to indicate the level of pressure above atmospheric pressure. See VACUUM GAUGE and COMPOUND GAUGE.
A passage that carries fluid from the source of flow to various operating elements of a fluid power system. Rated for operating pressure at the maximum expected pressure of the system.
The measure of pressure increase over the nominal setting of a device when additional fluid flow is passed over the device after it initially opens.
A side plate in a vane pump or motor cartridge on the pressure port side.
PRESSURE, PROOF TEST
A non-destructive pressure test applied to hose assemblies.
PRESSURE REDUCING VALVE
A pressure control valve whose primary function is to limit outlet pressure.
The peak value of a sudden increase of pressure in a hydraulic or pneumatic system producing a shock wave.
A digital device that opens or closes a switch when the internal pressure changes state.
An analog device that produces a change in voltage or current when the internal pressure changes state. Normally a fast response device for use in servo control systems. See PRESSURE TRANSMITTER.
An analog device that produces a change in voltage or current when the internal pressure changes state. Normally a slow acting device for use in display systems where update time is not crucial. See PRESSURE REDUCER.
PROGRAMMABLE LOGIC CONTROLLER (PLC)
A valve which controls and varies pressure, flow, direction, acceleration and deceleration from a remote position. They are adjusted electrically and are actuated by proportional solenoids rather than by a force or torque motor. The output flow is proportional to the input signal. They provide moderately accurate control of hydraulic fluid.
A non-destructive level of pressure at which a component, pipe, tube, hose or other fluid passage will not yield during testing of internal pressure. Normally 2 times working pressure. See WORKING PRESSURE and BURST PRESSURE.
In a filter, the condition where part of the flow passes through the filter element in proportional to pressure drop.
A valve which controls and varies pressure, flow, direction, acceleration and deceleration from a remote position. They are adjusted electrically and are actuated by proportional solenoids rather to the input signal. They provide moderately accurate control of hydraulic fluid.
Polytetrafluoroethylene, a high molecular weight fluoroplastic polymer with carbon atoms shielded by fluorine atoms having very strong interatomic bonds, giving it chemical inertness.
PULSE WIDTH MODULATION
An electronic signal of constant frequency and amplitude that has varying pulse width to control the level of power to the solenoid.
A mechanical device containing two sets of isolated pistons and control valving that are used to intensify fluid pressure by use of a multiplication effect across the two sets of pistons. The air piston being larger than the fluid piston.
PUMP, FIXED DISPLACEMENT
A mechanical device that creates a flow of fluid when its shaft is rotated in the proper direction and when its inlet is connected to a chamber filled with fluid (a reservoir or tank). The outlet port may be connected to a passage leading to a fluid power system or exhausted into another chamber that is at a higher pressure. The higher pressure chamber must be equipped with a pressure limiting device. The output flow rate is fixed by the pump displacement per revolution.
A mechanical device that creates a pressure that is lower than atmospheric at its inlet when the shaft is rotated. The outlet port is normally connected to a higher pressure chamber or atmosphere.
PUMP, VARIABLE DISPLACEMENT
A mechanical device that creates a flow of fluid when its shaft is rotated in the proper direction and when its inlet is connected to a chamber filled with fluid (a reservoir or tank). The outlet port may be connected to a passage leading to a fluid power system or exhausted into another chamber that is at a higher pressure. The higher pressure chamber must be equipped with a pressure limiting device. The output flow rate is fixed by the pump displacement per revolution but variable by the operator in a manual or servo controlled system, depending on the design.