Glossary D

Destaging - the removal of one, or more, impeller/s in a multi-stage pump to
reduce its differential head, or differential pressure.

Displacement - the change in position or location of an object relative to its neutral
position. It usually refers to the peak-to-peak displacement of a motion, or
vibration, and measured in mils or micrometers.

DN factor - the product of bearing bore diameter (*) in millimeters and its rotative
speed in  revolutions per minute (RPM). The DN factor is used as an index for
selecting the type of radial bearings to be used in centrifugal pumps. Ball
bearings are acceptable to use where the DN factor is 500,000 or less, whereas
sleeve bearings are recommended where the DN factor exceeds 500,000. Also
sometimes referred to as
ND factor. Read more.

 * use mean diameter for ball bearings; use ID for sleeve bearings

Double row, deep groove, ball bearing - a rolling element bearing that uses two
rows of balls positioned to allow the load to be transmitted through the balls in an
outward converging contact angle for higher thrust load capacity.

Double suction impeller - an impeller with two inlet , or suction, and where liquid
enters the impeller from both sides, as opposed to a single suction impeller
where liquid enters the impeller on one side only. Each side of a double impeller
is symmetrical by its centerline. Only radial impellers can be of double suction
single suction impeller.

Double suction pump - a pump with double suction impeller; on multi-stage
pump the double suction impeller may be on the first stage only. Only radial
pumps can be of double suction design. (The term
double suction does not imply
that the pump has two suction nozzles - it has only one suction nozzle..) See
single suction pump.





Engineering data


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Drawdown - the lowering of water surface level in a well due to pumping usage.

Drive collar - The part of cartridge seal that mechanically connects the seal sleeve
to the shaft to transmit rotation and prevent axial movement of the sleeve

Dry critical speed - API 610 defines dry critical speed as "a rotor natural
frequency calculated assuming that the rotor is supported only at its bearings and
that the bearings are of infinite stiffness." Simply stated, dry critical speed is the
rotor critical speed that does not take into account the dampening effects of the
pumped liquid, hence the word
dry. See wet critical speed.

Dual mechanical seal -  a seal arrangement using more than one seal in the
same seal chamber, in either double or tandem seal arrangement.

Dynamic unbalance - a condition where a rotor axis of inertia (centerline) is not
parallel to, and does not intersects, the rotor shaft centerline. The unbalance
exists in at least two planes, and can be corrected in at least two planes
perpendicular to the shaft centerline. Dynamic unbalance is the most common
type of mass unbalance occurring in centrifugal pumps.
Read more.

R: 0511-GLOD
C: glossary
F: glossary D1

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