NPSH and Cavitation

NPSH_{A} = \frac{p _{atm}}{γ} + z_{s} - h_{f s} - \frac{p _{v}}{γ}

Available NPSH at the pump inlet must exceed required NPSHR from the curve. zs is suction elevation relative to the pump (negative if the pump is above the sump). Cavitation when p_local < pv.

$z s$: Suction surface elevation vs pump datum
$h f s$: Suction-line losses
$p v$: Vapor pressure head

Step-by-step solved example

patm/γ=10.3 m, zs=−3 m, hfs=1.2 m, pv/γ=0.4 m. NPSHA?

NPSHA at the pump inlet — keep p > pv.

1. Sum
10.3−3−1.2−0.4=5.7 m.
$NPSH_{A} = 5.7 m$
2. Check
Need NPSHA > NPSHR plus a margin.

Answer: NPSHA = 5.7 m

10 practice questions

0/10 correct

1.Raising the pump relative to the sump

2.Hot water is worse because

3.NPSHR comes from

4.Cavitation damage is from

5.patm at sea level is about

6.Suction losses hfs include

7.A flooded suction (pump below the tank) has

8.If NPSHA < NPSHR the pump

9.Altitude lowers

10.Margin is often