NPSHa calculation for pump in parallel 3

417 · Aug 17, 2001

Hi, Can you please advise on how to calculate the head losses for two centrifugal pump connected in parallel to a common suction line? And also the NPSHa for the pump. The flow rate require is 500 liters/sec and the pump is 100m away from a reservior 5 m above the pump. The water is pump to two tanks one 200m away at 30m and the other 300m away at 50m. Currently the selected suction pipe size is 500mm.

Regards,
417

MJCronin · Aug 17, 2001

417,

To develop the NPSHa, I suggest that you calculate the pressure drop seperately in each pipe segment of the suction line. Consider the case where both pumps are running at he same time.

Use the methodology contained within "Crane Technical Manual #410" or visit the superb site

http://www.freecalc.com.

Calculate the TDH using the same methodology.

To get the NPSHr, contact various pump manufacturers with your required flow volume and the TDH you calculate for the system. Add about 5-8 ft to the NPSHr (as a safety margin) and compare it to the NPSHa that you calculated.

Purchase two identical pumps with the same size impeller. (Two pumps with different operating curves tend to "fight" with each other in parallel service) Tell the pump vendor that you intend to run these pumps in parallel.

Good Luck.......... let us know how well you do

MJC

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NPSHa calculation for pump in parallel 3

417

Mechanical

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