Ordliste

There are 16 entries in this glossary.
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Term Main definition
V-NOTCH IMPACT TEST
VALVE

A device which controls or isolates the flow of a liquid or gas in a conduit or pipeline.

VALVE SIZING

Size determination for a control valve for given process conditions shall be carried out in accordance with IEC standards where it is specified the prediction method of the achievable capacity for any size and style of control valve.

VAPOR PRESSURE

It is the pressure of a vapor in natural thermodynamic equilibrium with its condensed phase in a closed system. Vapor pressure varies with temperature.

VARIABLE ORIFICE

A small variable profile valve put in a flow line and used with a pilot to restrict the flow into the pilot and make the pilot more or less sensitive to changing conditions.

VEE-PACK
VENA CONTRACTA

It is the portion of a flow stream where fluid velocity is at its maximum and fluid static pressure and the cross-sectional area are at their minimum. In a control valve the vena contracta normally occurs just downstream of the actual physical restriction.

VENT PLUG

A special pipe plug having a small alien-wrench operated vent valve. These special plugs are located at the bottom of most ball valves. With the line valve closed (and under pressure) the body cavity pressure can be vented through this small valve to check tightness of seat seals or to make minor repairs. Having vented the body pressure the vent plug may be removed to blow out debris and foreign material or to flush the body cavity. On some gate valves the vent plug is installed on the bonnet for the sole purpose of venting the body. Such valves have separate drain valves. See Block and Bleed and Drain Plug.

VENTURI VALVE

A reduced bore valve having a bore smaller in diameter than the inlet or outlet. The flow through a venturi valve will be reduced because of the smaller port.

VICKERS HARDNESS TEST

A standard method for measuring the hardness of metals particularly those with extremely hard surfaces. The surface is subjected to a standard pressure for a standard length of time by means of a pyramid-shaped diamond. The diagonal of the resulting indention is measured under a microscope and the Vickers Hardness value read from a conversion table.

VISCOSITY

A measure of the internal friction of a fluid or the resistance of a fluid to flow. Two fluids of identical specific gravity may have quite different viscosities.

VISUAL EXAMINATION TEST (VT)

Examination of parts and equipment for visible defects in material and workmanship.

VOLUMETRIC NOE

Examination for internal material defects by methods such as radiographic and/or ultrasonic testing.

VOS (Valve Data Sheet)

A data sheet defining the minimum level of a valve design requirements including the materials testing inspection and certification.

VOTING SYSTEMS

Applied to high integrity control systems where a valve closure requires more than one command signal to operate. Typically 2 out of 3 to alleviate a single component failure.

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