NPSHr-diaphragm pump

[Das125]

Is there a way how to calculate NPSHr for diaphragm pump(some formula,figure..)? Or is it possible to get NPSHr only through testing?
And one more question: When I have NPSHr for water, how do I recalculate it for different liquid and temperature?
Thank you

 

[LittleInch]

Oh dear. You really don't know very much about NPSR by these questions.

You find NPSH by testing

For a PD type pump you also need to consider acceleration head as the fluid starts and stops very quickly as each stroke / movement starts and stops. This can be very significant.

NPSH is given in feet or metres head.

You calculate head depending on the fluid and part of the calculation need vapour pressure which is usually dependant on fluid temperature.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

"When I have NPSHr for water, how do I recalculate it for different liquid and temperature?"

Pls refer to Perry Chem Engg Handbook 7th edn fig 10-25 on page 10-23.

 

[1503-44]

You don't.

You calculate NPSH available, NPSHA. Then you compare that to NPSHr. Head is Head, no matter what the fluid, because the NPSHa head calculation already has a fluid's specific gravity included and SG is relative to water.

NPSHr is determined by testing using cool water, so its all "apples to apples".

 

[Wkcoo]

I believe pump manufacturer will have stated the npshr in the datasheet. But do clarify if that has included the acceleration head (usually it has not) if you have a very narrow margin.

 

[DRhodes]

The manufacturer will have the NPSHr for their pump. It will not include the acceleration head, this will be in the NPSHa equation. If you have access to a Cameron Hydraulic Databook it will have the equations you need.

 

[1503-44]

Correction.

Include density corrected for temperature in NPSHa calcs if there is a significant difference. Temperature may affect that calc most by changing your products vapor pressure.