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The following definitions are intended to give basic understanding of the terms
commonly used in the pump industry. Some industry standards, or customer
specifications, may have specific meaning of certain terms that may be different
from their common usage - in such case the terms should be interpreted in the
context of the standards, or specifications, being referred to.
Vane pass frequency - the frequency corresponding to the number of vanes
of an impeller multiplied by the impeller rotating speed. Example, an impeller with
five vanes rotating at 3560 RPM has a vane pass frequency of 5 x 3560 =
17,800 cycles per minute. In a multistage rotor with different impellers, each
impeller has a unique vane pass frequency depending on its number of vanes.
Many pump vibrations occur at impeller vane pass frequency. Also referred to
as blade pass frequency.
Vapor lock - a condition whereby the formation or release of vapor in the
suction of an impeller, due to cavitation or suction flow recirculation, diminishes
or prevents the suction flow from entering the impeller thereby resulting in the
loss of pump capacity.
Velocity head -
Vertical canned pump - a vertical pump of a double casing type consisting of
an inner bowl and an outer barrel. The bowl(s) containing the impeller(s), is
under compressive pressure from the liquid in the barrel which is under full
discharge pressure. A similarly designed horizontal pump is usually referred to
as barrel pump.
Vertical lineshaft pump -
Vertical pump - a pump whose shaft is mounted in vertical position.
Vibration signature - see vibration spectrum.
Vibration spectrum - a plot that shows the various vibration amplitudes in the
y-axis and their corresponding frequencies in the x-axis. Typically, the vibration
amplitudes are shown in mils and their frequencies are shown in cycles per
minute. The frequencies of interest are normally in the order of running speed
(X) such as 1X, 2x, (impeller vane number)X, etc. Vibration spectrum is also
referred to as vibration signature as it is used in identifying the source, or
cause, of high vibration levels in rotating equipment.
Vertical split – a horizontal pump whose casing and cover are split in vertical
position; same as radially-split horizontal pump.
Viscosity – see separate article on viscosity.
Viscosity correction -
Volume – see case volume.
Volumetric efficiency -
Volute - a spiral shaped pressure containment casing that houses an impeller.
Its main function is to collect, contain, and direct the flow of liquid coming out of
the impeller discharge. A volute with single throat area (or lip) is referred to as
single volute, while a volute with two throat areas (or lips) usually located 180
degrees apart are referred to as double volute. Double volute design provides
better radial thrust balance.
Volute A-gap -
Volute B-gap -
Volute cutwater - see cutwater.
Volute diffusion –
Volute, double -
Volute insert - an insert welded adjacent to a volute lip to drastically reduce
the volute throat area of a centrifugal pump. The insert may be cast, fabricated,
or cut by means of electric discharge machining (EDM) to blend smoothly with
the contour of the volute lip. The use of volute inserts is a relatively new
technology gaining increasing use in hydraulic re-rates to effect drastic
reductions in pump capacity in conjunction with using lower flow impellers. Also
referred to as volute lip insert.Volute pump - a pump whose casing is of volute
design that has either a single lip (single volute) or two lips (double volute), as
opposed to a diffuser pump that has multiple lips called diffuser vanes.
Volute lip –
Volute lip clearance -
Volute modification –
Volute, single -
Volute splitter –
Volute throat area -
Vortex - a whirling mass of liquid, or the whirling motion of liquid. Vortices are to
be avoided, or at least minimized, especially on the suction side of a pump, to
prevent cavitation and other pump performance impairment.