Oil & Gas Terms in Category V


A device used to determine the viscosity of a substance.

Also called a viscosimeter.

Vee ring

An elastomer (seal) energized by pressure

Vapor recovery unit

A device that removes mists and vapors from gas in a tank or enclosure.


An opening at floor level in a side of a derrick or mast.

The v-door is opposite the drawworks and is used as an entry to bring in drill pipe, casing, and other tools from the pipe rack.

The name comes from the fact that on the old standard derrick, the shape of the opening was an inverted v.



A cavity in a rock.


A small cavern, larger than a pore but too small to contain a person.

Typically found in limestone subject to groundwater leaching.

V-g meter

See direct-indicating viscometer, vibrating screen; see shale shaker.


Not susceptible to or affected by vapors.

For example, an electrical switch is made vaporproof so that a spark issuing from it will not cause an explosion in the presence of combustible gases (vapors).


A measure of the resistance of a fluid to flow.

Resistance is brought about by the internal friction resulting from the combined effects of cohesion and adhesion.

The viscosity of petroleum products is commonly expressed in terms of the time required for a specific volume of the liquid to flow through a capillary tube of a specific size at a given temperature.

Van der waals force

Attraction created by the weak electrostatic forces of distributed charge in a polar molecule.

Even though the water molecule as a whole is neutral, the polarity or the molecule leads to attraction between individual molecules from slight negative and positive centers.

This enters into effects of viscosity and surface tension.

Vapor recovery unit

A system composed of a scrubber, a compressor and a switch.

Its main purpose is to recover vapors formed inside completely sealed crude oil or condensate tanks.

the switch detects pressure variations inside the tanks and turns the compressor on and off.

The vapors are sucked through a scrubber, where the liquid trapped is returned to the liquid pipeline system or to the tanks, and the vapor recovered is pumped into gas lines.


A fluoroelastomer capable of sealing in sour gas, volatile adj: readily vaporized.

Valence effect

In general, the higher the valence of an ion, the greater the loss of stability to emulsions, colloidal suspensions, etc., these polyvalent ions will impart





The timed rate of linear motion.

Viscous flow

See laminar flow.


A device used to control the rate of flow in a line to open or shut off a line completely, or to serve as an automatic or semiautomatic safety device.

Those used extensively include the check valve, gate valve, globe valve, needle valve, plug valve, and pressure relief valve.