I am running the pump at different RPM using VFD but at one condition my pump shut off head comes in negative how i can increase my pump shut off head??
Negative to what exactly? Can you sketch the pump curve? Why not just increase speed? I'm sorry but the question needs figures and data for it to make sense to a stranger.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
Aha, yes, a suction lift service. If so, then the problem is on the suction side (where most puzzling pump problems originate), and usharma007 needs to address NPSH issue or just don't slow down the pump to that point.
Of course a little bit of input from usharma007 would go a long way in solving the mystery.
Yes. Also maybe not enough suction flow to keep velocities high enough to sweep ingested air bubbles along, producing a vapor lock in the suction piping at a high point. At this point the possibilities are endless.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
Yes it is a bit hard to get away from suction side, suction lift, suction flow etc, of course this doesn't create any problems to those who understand what is meant not what is said.
Dictionaries don't seem to help - for interest just checked my "bible" of English language and guess what - "if something sucks a liquid, gas or object in a particular direction, it draws it there with a powerful force." seems we are losing on all fronts. Now considering an email to the publishers pointing out that the description could be / should be changed to correct the misinformation.
It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)
