Glossary U

Unbalance - the uneven mass distribution on a rotating element that will cause it
to vibrate due to centrifugal force when the element is rotating. The magnitude of
vibration increases proportionately with unbalance mass and rotational speed.
Unbalance is the product of the unbalance mass multiplied by its distance from
the axis of rotation, or shaft centerline, and is commonly measured in
ounce-inches. See
residual unbalance. Read more.

Unbalanced seal - a mechanical seal that is not hydraulically balanced to
minimize the heat developed at its seal face.

Undercut, or undercutting - trimming the effective diameter of an impeller by
cutting its vanes only, and leaving its shroud uncut.

Underfile, or underfiling - the removal, by hand-grinding, of some amount of metal
on the impeller vanes, either on the inlet side, or outlet side, for the purpose of
reducing the vane thickness and increasing the area opening between two
adjacent vanes, to change the performance of a pump.

Unfiltered vibration - vibration data that include the spectrum of different
frequencies under observation. By comparison, filtered vibration data are unique
to a discreet, or specific, frequency under observation.

Upstaging - the addition of one or more impeller/s to previously de-staged
multistage pump to increase its differential head. (See definition of de-staging.)

R: 0411-GLOU
C: glossary
F: glossary U1

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