Pump curve 4

[asifraza0]

Hello Experts:

I need an expert opinion: I have a centrifugal pump running in thermic fluid service. The original design data sheet indicates the pump was sized for 300 GPM at 171 feet of diff head. The design of the pump is based existing and future expansion project. The expansion is yet to come. Having said that, the pump was put into service and the pump operated at 650 gpm at 100 feet of head. This was beyond the maximum allowable the pump could handle. The pump was operating very far right hand side of the curve. This resulted in shaft deflection and mechanical seal failures. The problem was diagnosed and the pump was put back on curve. Now the pump is operating at 480 GPM and 150 feet of head and very close to BEP. Currently the pump operation is very quiet and running smooth as a silk
Questions -
1) Is there any advantage in moving pump more towards the left hand side of the curve more closer to 300 GPM, the original design
2) If Nothing was done and the pump kept churning around 480 GPM; is there any concern with respect to higher velocity in the pipes and cavitation due to higher pressure drop in the suction. Since the piping size and the NPSH requirement is based on 300 GPM but in reality the output is 480 GPM

Thanks in advance for all your help
Araza



Asif Raza

 

[LittleInch]

Somethings not right here.

If the system curve is the thin line starting at 0 and going up then its showing at 120ft you only have about 240 gpm.

Or to get 330 gpm you need a pressure of over 200ft which is more than the pump can supply.

The pump is still basically the wrong one for the duty as the BEP is around 550 gpm. If your max flow is 330 then you're always going to be quite inefficient and if this is a continuous duty or heavy duty pump then you'll loose a lot of power compared to the right pump.

However if the line is just drawn wrong and your figures are correct (330 gpm @ 120ft) then the VFD is a bit better, but the pump is still just too big.

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

 

[Artisi]

without re-reading the whole story as to the why's and wherefores', if the curve posted representing the friction loss curve is correct it is obvious that the pipework is way undersized for the flowrates.

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.)