calculation of npsh

NPSH (a) is 1 psi for every 3 feet of vertical rise of system coming into the pump inlet.

NPSH (r) is a function of the pump design please go to the GOULDS pump web site they have a lot of good info.

Try this link -- it has a full explanation with charts, formulae, and more. http://www.mcnallyinstitute.com/11-html/11-12.html

NPSH(a) Net Positve Suction Head (available) Is the total head (pressure) available this is atmospheric pressure (10m) at sea level plus whatever height the source is above the pump. Net Positive Suction Head (required) is given by the pump manufacturer on their performance curves . From this you can determine the suction lift you can effectivley get from your pump without cavitation damage. In practice 5-6 m is as far as you should should suck water. Also keep the suction pipework a size larger than the delivery pipework with as few bends as possible and it must be airtight with a good quality foot valve that doesnt restrict the flow fitted.

NPSH is calculated as follows

H=Pbx10.2-NPSH- Hf-Hv-Hs

pb is the barometric pressure in case of tanks its the atmospheric pressure

NPSH - To be read from the NPSH curve of the pump at the highest flow the pump will be delivering .

Hf- friction losses in suction pipe , elbow , valves etc

Hv-Vapour pressure at that temperature almost at room temperature

Hs-Safety margin of 0.5 mts

If the calculated H is positive then the pump can operate at suction lift of maximum "H" mts head.

If the calculated H is negative then an inlet pressure of minimum "H" mts head is required .

hope its clear

Ayub