5
®
Minimum inlet pressure NPSH
Minimum nominal flow rate
To avoid cavitation, make sure that there is a minimum
pressure on the suction side of the pump.
NPSHA: Net Positive Suction head Available
The net positive suction head available is a function of
the pump suction system.
NPSHR: Net Positive Suction head required
The net positive suction head required is a function of
the pump design at the operating point on the pump
performance curve.
NPSHA=Ha-Hs-Hf-Hv-Hst (in meters head)
Ha: Barometric pressure.(That can be set to 10.2 m.)
Hs: Suction lift.
Hf: Friction loss in suction pipe.
Hv = KT+KH: Vapor pressure
KT: Flow resistance due to liquid temperature.
KH:Flow resistance due to elevation above sea level.
If the liquid is water, you can consult the tables to determine
the values of KT and KH.
To prevent overheating of the internal pump components,
the pump should not be used at flows below the minimum
flow rate.
Do not run the pump against a closed
discharge valve for longer than a few seconds.
The curve shows the minimum flow rate as a percentage of
the nominal flow rate in relation to the liquid temperature.
40 60 80 100
10
20
Qmin
[%]
t [°C]
30
120 140
0
T (C) 20 30 40 50 60 70 80 90 100 110 120
KT (m) 0.2 0.4 0.8 1.3 2.2 3.3 5 7.4 11 15 22
H (m) 0 500 1000 1500 2000 2500 3000
KH (m) 0 0.55 1.1 1.65 2.2 2.75 3.3
Hst: Safety margin. (minimum: 0.5 meters head)
NPSHA ≥ NPSHR: Pump running will be fine.
NPSHA < NPSHR: The pump will be dry running or cavitating.
Stop operation of the pump if cavitation occurs.
Cavitation will cause pump damage and the resultant damage is not subject to warranty.
40 60 80 100
10
20
Qmin
[%]
t [°C]
30
120 140
0
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