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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.
NDE - see Non-Destructive Examination.
ND factor - another name for DN factor. See DN factor.
Net Positive Suction Head Available (NPSHA) - the total absolute suction
pressure, minus the vapor pressure, expressed in the unit of head (feet) of the
pumped liquid, and referred to a datum elevation. The datum elevation is usually
the impeller centerline on a horizontal pump, and either the suction nozzle
centerline or top of foundation on a vertical pump. See NPSHR.
Net Positive Suction Head Required (NPSHR) - the net positive suction
head (NPSH) required by a pump without impairing its performance due to
cavitation. Impairment is said to occur when the pump suffers a loss of head
equal to 3% of the head of the first stage impeller at a given flow rate. The
NPSHR is usually referred to the impeller centerline. See NPSHA.
Newtonian liquid - a liquid whose viscosity is independent of the rate of shear
at a given temperature. Shear is the movement of one layer of liquid relative to
another layer when a shearing force is applied. Examples of Newtonian liquids
are water and light oil. See non-Newtonian liquid.
Nitrogen leak test - see air leak test.
Non-destructive examination (NDE) - see separate article.
Non-Newtonian liquid - a liquid whose viscosity is dependent on the rate of
shear at a given temperature. Shear is the movement of one layer of liquid
relative to another layer when a shearing force is applied. Examples of
non-Newtonian liquids are paint, grease, molasses, clay slurries, etc. See
Normal operating point - the point at which the pump operates most of the
time, or under normal operating conditions. This is different from the rated
operating condition which is the point at which the pump performance is
guaranteed by the pump vendor subject to the performance tolerance of the
applicable standard or user specification.
Nozzle head - the part of a vertical barrel pump that contains the suction and
discharge nozzles, and where the driver is mounted. The nozzle head is
mounted on top of the barrel.
NPSHA - see Net Positive Suction Head Available.
NPSHR - see Net Positive Suction Head Required.
NPSHR3 - the net positive suction head required by a pump based on three
percent (3%) head loss.