Glossary V


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
.

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 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.

Viscosity (click on link to read full article)

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 cutwater - see cutwater.

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.

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.


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C: glossary

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