Vacuum: A pressure of less than one atmosphere.
Vane passing syndrome: Cavitation caused by the clearance between the impeller and the cutwater being too small.
Vane pump (hydraulic): A positive displacement pump that consists of vanes mounted on a circular rotor. The rotor sits inside a circular cavity. These two circles are offset, to create eccentricity.
Vaporise: Fluid changes state from liquid to gas.
Vapor pressure: If a liquid is in a chamber that is below the vapor pressure, then the liquid will vaporize.
Variable speed motor: Can be used to control flow in the system by varying the impeller speed.
VDMA: The German Engineering Federation. It’s the trade association for the German mechanical engineering industry.
Velocity: Typically used to mean speed, but also includes directionality.
Velocity head: The energy contained in a flowing fluid. Its kinetic energy. Calculated by the term (velocity)2 /2 (acceleration of gravity).
Vent: To remove air or gas from a mechanical system.
Venturi (Bernoulli's law): A pipe that has a section in its middle of smaller diameter than either end. The pressure in this area will be less than the pressure in the area of piping with the larger diameter.
Vertical canned pump: A vertical pump that has a double casing composed of an inner bowl and an outer barrel. The outer barrel, under full discharge pressure, compresses the liquid in the inner bowl.
Vertical pump: Any pump where the shaft is mounted vertically.
Vibration Damping: Important in mechanical seal design to prevent seal faces from opening and leakage occurring.
Vibration spectrum: A plot of amplitude of vibration vs frequency. Sometimes this is referred to as a vibration signature and it can be used to identify the source, or cause, of high vibration levels in turbomachinery.
Viscosity: Resistance to gradual deformation of a fluid by shear or tensile stress.
Viscous drag pump: A pump design that uses a flat impeller containing no vanes. The fluid is moved by interacting with the flat disk of the impeller through its viscosity.
Viton®: An elastomer brand name manufactured by E.I. Dupont Dow. Generically known as a fluorocarbon.
Volute: A spiral shaped container that houses the impeller. Its function is to collect and direct the flow of liquid coming out of the impeller.
Volute casing: Converts energy from the velocity of a fluid into pressure by using the venture effect.
Volute insert: An insert welded at the volute lip to change the pump performance. It’s a new technology used to effect reductions in capacity of re-rated pumps.
Volute pump: A pump design where the casing is shaped like a volute (spiral). Can contain either a single lip or two lips.
Vortex: A mass of liquid in rotary motion around an imaginary axis. The flow is referred to as vertical flow.
Vortexing liquid: Refers to the inlet where a liquid that is vortexing, may draw air into the intake.
Vortex pump: A pump used in applications where a very large percentage of solids are contained within the fluid. Operates by having a recessed impeller that is out of the flow path.