Vacuum

A system is under vacuum when its pressure is below that of the surrounding atmosphere. The lower the pressure, the higher the vacuum.

Valves

Devices to control or regulate the flow of liquids or gases through pipes. The main types are diaphragm, gate, globe, butterfly, check, ball, plus and relief.

Vapour

Substance in a gaseous state.

V-belt

A belt with a trapezoidal cross section that is made to run in sheaves, or pulleys, with grooves of corresponding shape. See belt.

V-door

The opening in the derrick opposite the drawworks used for bringing in drill pipe and casing from the nearby pipe racks.

Velocimeter

An instrument used for the "in situ" measurement of the speed of sound in the sea and other natural waters.

Velocipede

Instrument using a probe lowered to the sea-bed and used to calibrate echo sounders; may be called TDS or CTD dip as it measures temperature, depth and salinity (or conductivity); in most waters (less than 1000 m), depth is the least significant of these factors to compute velocity; some instruments measure velocity directly.

Velocity

1. Of sound in sea water (velocipede). 2. Seismic velocities, also acoustic (two way time).

Vent losses

Acid gas which is being vented.

Venturi meter

An instrument for measuring the volume of flowing gases and liquids. It consists of two parts -the tube through which the fluid flows and a set of indicators which show the pressures, rate of flow or quantity discharged. The tube, in the shape of an elongated hour glass, is flanged into a pipeline carrying the fluid. The effect of the tube is to increase the velocity and decrease the pressure at the point where the tube's diameter is reduced. The relationship between the line pressure and the narrow "waist" of the tube is used in computing the rate of flow.

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