A–B–C–D–E–F–G–H–I–J–K–L–M–N–O–P–Q–R–S–T–U–V–W–X–Y
Potentiometer
The principle of its operation is that a voltage gradient is generated across a resistive element which has a variable pick off point connected to the valve stem. As the stem moves, the voltage changes across the potentiometer to provide an electrical output of the valve position.
Power Operator
Powered valve operators are of the following general types: Electric Motor, Pneumatic or Hydraulic Motor, Pneumatic or Hydraulic Cylinder. Operators can either be adapted directly to the valve stem or side mounted on existing gear or scotch-yoke operators.
Power Supply
The device which provides power to a control system or component.
Pressure Containing Parts
Parts such as bodies bonnets, glands, stems, gaskets and bolting designated to contain the pipeline fluid.
Pressure Controlling Parts
Parts such as seat and obturator intended to block or permit the flow of fluids.
Pressure Drop
The decrease in pressure along the direction of flow in a piping system caused by fluid friction restrictions and by change-of direction fittings. Pressure drop is related to velocity-specific gravity viscosity and to the size and roughness of the pipe interior. See Differential Pressure.
Pressure Reducing Regulator
Regulator designed to control downstream pressure.
Pressure Relief Valve
A safety device required on most pressure systems and is preset to relieve the line pressure should it exceed that limit.
Pressure Switch
A switch (usually electric) activated by a rise or drop in pressure. A transducer.
Pressure Test
A test using specified pressures of liquid or gases which can be used to check sealing, integrity, design standards etc. of a particular product.
Primer
First coat of paint applied to a surface, formulated to have good bonding and wetting characteristics may or may not contain inhibitive pigments.
Process Wetted Parts
Parts exposed directly to the fluid flowing in the line i.e. ball or gate or seats.
Product Analysis
A verification conducted by the valve manufacturer to assure that the chemical composition of received material coincides with the heat analysis and with the requirements of the applicable specification.
Proof Pressure
A hydrostatic test pressure usually 1.5 times the rated working pressure applied to an assembled valve to verify the structural integrity of the pressure containing parts. Synonymous with Hydrostatic Shell Test.
Protective Sleeves
A circular “pipe like” sleeve inserted in place of the ball and seats of a top-entry ball valve. This protective sleeve remains in place inside the valve during valve installation and ultimate pigging of a pipeline to clear debris from the line before placing the pipeline into service. Once the pipeline has been purged of all debris, the protective sleeve is removed entirely from the ball valve cavity and the operating trim (i.e. ball and seats) is then installed for normal service conditions.
Protocol
A definition of the rules by which master and slave units communicate with each other.
Proximity Sensor
A device that detects the presence of a target by it disturbing the associated magnetic field. Used as a limit switch and suitable for intrinsically safe circuits.
PSI (Pounds per Square Inch)
Unit of measure of pressure. Not a SI unit.
PTFE
The abbreviation stands for Polytetrafluoroethylene. It is a type of fluorinated thermoplastic, with outstanding chemical resistance, low leachability and excellent lubricity. It has a maximum temperature limitation of 500ºF.
Pulsation
Rhythmical throbbing or vibrating in pipelines flow or pressure oscillation which is identically repeated in every fixed time interval. Pulsation is an inherent characteristic of reciprocating gas compressors and reciprocating liquid pumps. Pressure and flow pulsations interact with piping systems to cause vibration, metering errors and potential equipment damage.
Pump Control Valve
A ball valve that is not meant for on-off service, but whose specific function is to control flow and prevent cavitation in pumps on liquid pipelines.