Goulds Pumps SVT-1SV Technical Manual page 86

Commercial Water
TECHNICAL DATA – NPSH
NPSH
The minimum operating values that can be reached at the
pump suction end are limited by the onset of cavitation.
Cavitation is the formation of vapor-filled cavities within
The vapor-filled cavities flow with the current and when
they reach a higher pressure ares the vapor contained in
the cavities condenses. The cavities collide, generating
pressure waves that are transmitted to the walls. These,
formed and yield due to fatigue. This phenomenon, char-
acterized by a metallic noise produced by the hammering
on the pipe walls, is called incipient cavitation.
The damage caused by cavitation may be magnified by
electrochemical corrosion and a local rise in temperature
due to the plastic deformation of the walls. The materials
that offer the highest resistance to heat and corrosion are
alloy steels, especially austenitic steel. The conditions that
trigger cavitation may be assessed by calculating the total
net suction head, referred to in technical literature with
chine under safe conditions, the following formula must
h + h (NPSHr + 2 ft) + h
p z
h
p
h is the suction lift between the pump axis and the free
z
pump axis.
h is the flow resistance in the suction line and its acces-
f
etc.
h
pv
0.5 is the safety factor.
-
-
-
+ h
f pv
-
L enntech
Goulds Pumps
The maximum possible suction head for installation de-
To help the user, with reference to water temperature
tables show the drop in hydraulic pressure head in relation
to the elevation above sea level, and the suction loss in
relation to temperature.
Water Temperature (ºF) 68 104
Suction Loss (ft) -.7 2.3
Elevation Above Sea Level (ft) 1600 3300 4900 6500 8200 9800
Suction Loss (ft) 1.8
To reduce it to a minimum, especially in cases of high suc-
with high flow rates, we recommend using a suction line
having a larger diameter than that of the pump's suction
port. It is always a good idea to position the pump as close
140 176 194 230 248
6.6 16.4 24.3 50.5 70.5
3.6 5.4 7.2 9.0 10.8
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