VERDER Verderair VA-E80, Operation

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Performance Charts
How How How to to to Calculate Calculate Calculate Your Your Your System’s System’s System’s Net Net Net Positive Positive Positive Suction Suction Suction Head Head Head –– – Available Available Available
(NPSHa) (NPSHa) (NPSHa)
For a given flow rate, there must be a minimum
fluid head pressure supplied to the pump to prevent
cavitation. This minimum head is shown on the
Performance Curve, labeled as NPSHr. The units are
meters WC (Water Column) absolute. The NPSHa of your system must be greater than the NPSHr to
prevent cavitation and therefore increase efficiency
and the life of you pump. To calculate the NPSHa of
your system, use the following equation:
NPSHa NPSHa NPSHa = = = H H H
a a a
± ± ± H H H
zz z
–– – H H H
fff
–– – H H H
vv vp p p
Where: Where: Where:
H H
Ha
a
a is the absolute pressure on the surface of the liquid in the supply tank. Typically, this is atmospheric
pressure for a vented supply tank, e.g. 10 meters at sea level.
H H Hzz z is the vertical distance in meters between the surface of the liquid in the supply tank and the centerline of
the pump inlet. Value should be positive if the level is higher than the pump and negative if the level is lower
than the pump. Always be sure to use the lowest level the liquid can reach in the tank.
H H
Hfff is the total of the friction losses in the suction piping.
H H Hvp vp vp is the absolute vapor pressure of the liquid at the pumping temperature. For example, for water at
21°C, the vapor pressure is 0.26 meters.
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