NPSHA vs NPSHR
NPSHA vs NPSHR
(OP)
Its known that in a positive displacement pump suction line must be take in account the acceleration head (ha)and substract it for the NPSHA. But, what is the value of NPSHA for comparison with NPSHR.
NPSHA = Pa+Hs-Pv-hf-ha?
or NPSHA = Pa+Hs-Pv-hf?
Why?
Thanks
Ciro
NPSHA = Pa+Hs-Pv-hf-ha?
or NPSHA = Pa+Hs-Pv-hf?
Why?
Thanks
Ciro





RE: NPSHA vs NPSHR
RE: NPSHA vs NPSHR
We deliver steam as if your life depends on it.
RE: NPSHA vs NPSHR
Actually Acceleration Head is the correct term, though it's used strictly (in my experience, anyway) in reciprocating positive displacement pump design as a way of describing the start-and-stop nature of suction flow into the pumps, i.e. on a simplex plunger pump the suction fluid is only moving during 180° of the crank rotation. It's additive onto the basic NPSHA calculation, frequently the dominant loss in the suction piping system, and is what usually causes a suction stabilizer to be required.
RE: NPSHA vs NPSHR
We deliver steam as if your life depends on it.
RE: NPSHA vs NPSHR
Acceleration head, on the other hand, is actually another loss of energy from that which was available in the suction vessel, over and above the steady-state line losses calculated based on friction and fluid velocity. It's subtracted the same way you subtract line losses. The interesting thing is that it's additive, the head lost as you accelerate the liquid from a stop is recovered as the liquid decelerates, minus some frictional losses, so by installing a suction stabilizer of some sort, you can gain back almost all the energy 'lost', and nearly neutralize the effect entirely.
However, since NPSH calcs rely on the worst case condition, only the losses associated from accelerating the liquid is considered, and deducted from the steady state NPSHA prior to comparison with NPSHR.