Ross Mackay Forum Moderator 94 Posts
Re: Pumps: Finding The Correct Net Suction Pressure22 May 2009 at 1:29pm
We may have a little nomenclature confusion, but I'm going to assume N.S.P. stands for Net Suction Pressure.
If that is correct, then I think the best way I can advise you on this is to lead you to my Article entitled "Net Positive Suction Head," which you can find on my Web site www.practicalpumping.com/articles.php.
That article clearly spells out the way to determine Net Positive Suction Head, and it does require you to have the atmospheric pressure included as long as that is the pressure that is on the free surface of the liquid in the tower.
I am balancing condenser water pumps for a major city. The system is an open loop, with sump catch at the tower. It is approximately 15-feet down and 30-feet across. For the two pumps, required flow is 3400. G.P.M max flow combined on pumps is 3900 G.P.M required net suction pressure is 4.2 across each pump and 1.90 at each suction diffuser, total= 12.2 N.S.P. Correct gauge reading before pumps on suction full out is 5.2. G.P.M measured is 2700, sent N.S.P requirements in to design engineer who says we did not add into account atmospheric pressure and that is why we do not have the correct N.S.P. What of this atmospheric pressure shouldn't already be added into the gauge reading at the suction line? Is this an accurate statement by the design engineer?
Have an insight or suggestion?
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