Glossary D
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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.
center before undertaking maintenance, repair, or upgrade work on a pump.
Pump decontamination should be done prior to performing any DCI.



Design -

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

Destaging pieces

Destaging tube


Differential head -


Diffuser pump

Diffuser ring -

Diffusion angle

Diffusion area ratio -

Discharge angle

Discharge flow -

Discharge flow recirculation

Discharge head -

Discharge nozzle -

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 case pump - a pump with two pressure containment boundaries, one
being inside another such as a barrel pump consisting of an inner casing
mounted inside a barrel.

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 design. See 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.

Double volute -


Dowel pin -

Drain connection

Driver -

Duncan hood

Duplex bearings

Duplex material -

Duplex stainless steel -

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