Understanding HPSHA & HPSHR

[DieselTwitch]

Im having a little bit of a problem understanding how these effect my design of the pumping system.

The pump im looking at has a NPSHR of 10' at 40GPM and rises to 20' 150GPM.

What does this mean. Is this the limit that I can place the pump at above the source before I get the fluid boiling under a vacuum?

My application (as part as my other post about turning a non-priming in to an auto-priming pump. ) is that I need to pump out of a sump that is 10 - 15' below where I will be mounting the pump. I also will be pumping out of a pond with the same pump that is only 3' below where the pump is mounted.

How does the NPSHR effect my application. I tried to watch some videos and read some articles on the subject but I am still at a loss to understand really what its telling me.

Here is the spec sheet of the pump I will be using. (the pump Im using will be Curve B.

http://www.wegotpumps.com/pdfs/87-88.pdf

Thank you for your help.

 

[JohnGP]

Basically you need to calculate your available NPSH under the various operating conditions, and check that those numbers are greater than the required NPSH as specified by the pump manufacturer at each condition (with a bit of a margin just to be sure).

There has been much discussion around NPSHR and NPSHA in this forum and on the internet - have a search - see

http://en.wikipedia.org/wiki/NPSH

for a bit of an explanation, but there is heaps out there.

Cheers,
John

 

[micalbrch]

Did you search for NPSH here at eng-tips.com? This issue has been discussed many times in the past and some colleagues here gave very good technical explanations and examples.

If the sump is 10-15' below pump's inlet the pump will cavitate if the NPSHR is not significantly higher than that or the pump will not work at all.

NPSHA is not just the geodetic height between fluid level and pump's inlet but the geodetic height is a very important part of it. Suction line diameter, length, no. of elbows and valves, fluid velocity, atmospheric pressure and vapor pressure of the fluid affect NPSHA, too. Assuming you could neglect all this, then the atmospheric pressure (in ft) minus suction lift would indicate NPSHA.

 

[DieselTwitch]

I did search but found no answer directly relating to my question. I think I have a better hold on what's going. However I did not search directly at eng-tips.com normally google pulls up topics on here of they relate. Could have missed it.

 

[BigInch]

No. Roughly using your terminology, it would be more like the reverse, it's the distance BELOW the source you must have to have to keep your pump operating, from which you must also subtract flow losses.

"The top of the organisation doesn't listen sufficiently to what the bottom is saying." Tony Hayward X-CEO BP
"Being GREEN isn't easy." Kermit

http://www.youtube.com/watch?v=hpiIWMWWVco

http://virtualpipeline.spaces.live.com

 

[Artisi]

Think you could have problems with the sump application, if the water level below pump is 10 - 15ft and NPSHr is between 10ft -20ft then NPSHa could be a problem.

The published curve on

http://www.wegotpumps.com/pdfs/87-88.pdf

is just a generic curve for brochure use, what you need is a pump curve for that particular pump from the manufacturer on which you will have to over-lay a system curve for combined inlet and discharge losses. this will show you where the pump will operate under actual conditions and will show if NPSHr exceeds or is less than NPSHa.

There are no short cuts in getting a real answer and wishful thinking never solved an NPSH problem.