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Minimum inlet pressure NPSH Print E-mail
Minimum inlet pressure NPSH
In case that the pressure in pump is lower that steam pressure used to convey liquid, the cavitations will occur.

To avoid the cavitations, and lessen the libration and noise, you are suggested to adopt NPSH to make sure that the pump are under optiomal operation condition.

The following formula can be used for calculation of minimum inlet pressure :
H = Pb x 10.2 - NPSH - Hf - Hv - Hs
H : maximum suction head (m)
Pb : Atmosphere pressure (bar)
In a closed system, Pb means system pressure (bar)
NPSH : Net positive suction head (m)
It can be read from the point of Max.flow rate shown on NPSH curve.
Hf : Pipeline loss at the inlet (m)
It is in accordance with pipelie possible Max.flow.
Hv : Stream pressure (m)
It depents on liquid temperature and system pressure value.
Hs : Safety margin (m)
Minimum 0.5m delivery head

If the calculated result H is negative, the pump may run under the Max.suction head H. In case the calculated result H is negative, a delivery head if Min.inlet pressure is necessary.
Note: Normally, the above calculation will not be done. H is calculated in the following conditions:
1. The liquid temperature is comparativelt higher.
2. Liquid flow exceeds rated value.
3. Suction head is comparatively large or inlet pipeline long.
4. System pressure is too low.
5. Bad inlet condition.
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