A pump station has been designed to lift water out of a 6 metre deep pit (vented

Question

A pump station has been designed to lift water out of a 6 metre deep pit (vented to atmosphere) via a centrifigual pump mounted at ground level.

Liquid conditions 20 OC

Suction pipe work losses 2.0 metres

NPSH safety factor 5.0 kPa

Vapor pressure @ 20oC 0.25 metres

Calculate the Net Positive Suction Head (NPSH) for the system ?

In summer the liquid temperature rises to 60 oC, this changes the water vapor pressure to 2.05 metres. What is the revised NPSH for the higher water temperature ?

Pressure loss in the suction pipe work is directly proportional to water veloicty in the pipe work squared, which is inversely proportional to suction pipe work diameter squared.

Explanation / Answer

NPSH=Ha-Hv-hs-hfs

=6-2.05-2-0.25=1.7m

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