An electric switch operated by fluid pressure.


Related Terms

PNEUMATIC CONTROL VALVE

A valve in which the force of compressed air against a diaphragm is opposed by the force of a spring to control the area of the opening for a fluid stream.

PNEUMATIC DRILLING

Drilling a hole when using air or gas in lieu of conventional drilling fluid as the circulating medium; an adaptation of rotary drilling.

PLUMMET

A loose-fitting metal plug in a tapered rotameter tube which moves upward (or downward) with an increase (or decrease) in fluid flow rate upward through the tube. Also known as float.

PLUG VALVE

A valve fitted with a plug that has a hole through which fluid flows and that is rotatable through 90 for operation in the open or closed position. Also known as plug cock.

PLUG METER

A variable-area flowmeter in which a tapered plug, located in an orifice and raised until the resulting opening is sufficient to handle the fluid flow, is used to measure the flow rate.

PITOT TUBE

An instrument that measures the stagnation pressure of a flowing fluid, consisting of an open tube pointing into the fluid and connected to a pressure-indicating device. Also known as impact tube.

PISTON PUMP

A pump in which motion and pressure are applied to the fluid by a reciprocating piston in a cylinder. Also known as reciprocating pump.

PIEZOMETER

1. An instrument for measuring fluid pressure, such as a gage attached to a pipe containing a gas or liquid. 2. An instrument for measuring the compressibility of materials, such as a vessel that determines the change in volume of a substance in response to hydrostatic pressure.

PERMEATE

The clear fluid that passes through the membrane in a membrane filtration process.

PECLET NUMBER

Dimensionless group used to determine the chemical reaction similitude for the scale-up from pilot-plant data to commercial-sized units; incorporates heat capacity, density, fluid velocity, and other pertinent physical parameters.

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