Vaccum: Pressure lass than atmospheric pressure. It is usually expressed in inches of mercury (in Hg) as reffered to the existing atmospheric pressure.

Valve: A device which controls fluid flow direction, pressure, or flow rate.

Velocity: The speed of flow through a hydraulic line. Expressed in feet per second (fps) or inches per second (cps). The speed of a rotating component measured in revolution 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 flow from a component.

Viscocity: A measure of the internal friction or the resistance of a fluid to flow.

Viscous Damping: Inherent losses are present in all motors which result in lower torque delivered at the output shaft than developed at the rotor. Losses which are proportional to speed(i.e. speed dependent terms such as windage, friction, eddy current) are related through the motor's viscous daming constant, measured as the slope of the damping curve.

Voltage: The amount of electromotive force (emf) produced by a power source or available at points in a circuit, expressed in units volts.

Voltage Constant: K_E = The back EMF generated by a DC motor at a defined speed. Usually a quoted in volts per 1000rpm.

Volume: The size of a space or chamber in cubic units. Loosely applied to the output of a pump in gallon per minute (gpm).