Glossary and index of fluid power principles and components V

VACUUM
Pressure less than atmospheric pressure. It is usually expressed in inches of mercury (Hg) as referred to the existing atmospheric pressure.

VACUUM GAUGE
A visual indicator of pressure that is set for `zero' psi at atmospheric pressure and includes a dial which will continue to indicate the level of pressure below atmospheric pressure.

VALVE
A mechanical device that is used in a fluid power system, which is used to provide some change of state of the fluid.

VAPOUR PRESSURE
The measure of pressure at which a specific fluid will change to a gas.

VARIABLE
A factor or condition which can be measured, altered or controlled, i.e., temperature, pressure, flow, liquid level, humidity, weight, chemical composition, color, etc.

VELOCITY
The speed of fluid flow through a hydraulic line. Expressed in feet per second (fps), inches per second (ips), or meters per second (mps). Also, the speed or a rotating component measure in resolutions per minute (rpm).

VENT
To permit opening of a pressure control valve by opening its pilot port (vent connection) to atmospheric pressure.An air breathing device on a fluid reservoir.-To remove trapped air from a component.

VENT VALVE
A valve that may be manually opened to allow air or fluid or a combination of both to be exhausted into a lower pressure chamber or to the atmosphere.

VIBRATION
Amplitude motion occurring at a given frequency

VISCOSITY
The measure of resistance to flow of a fluid against an established standard. See SUS and SSU.

VISCOSITY INDEX
A measure of the viscosity-temperature characteristics of a fluid as referred to that of two arbitrary reference fluids (ASTM Designation D2270-64).

VOLTAGE
-The size of a space or chamber in cubic units. -Loosely applied to the output of a pump in gallons per minute (gpm) or liters per minute (LMP)

VOLUME
The size of a space or chamber in cubic units. Loosely applied to the output of a pump in gallons per minute.

VOLUMETRIC EXPANSION
The volume increase of hose when subjected to internal pressure.

VULCANIZATION
A process during which a rubber compound, through a change in its chemical structure improves or extends elastic properties over a greater range of temperatures.