by Lev Nelik

In the October 2008 issue, we evaluated efficiency and energy savings for a typical centrifugal pump ("Efficiency, Energy and Life Cycle Cost"). Many said the Energy Estimator helps when dealing with common energy cost issues.

What happens to efficiency, however, when you try to deliver the same flow and head but at different speeds? Will it change the pump size (impeller diameter) and how?

For Pump Challenge #3, click here.  

Suppose you are trying to deliver 4,000 gpm at 400 ft. Would it be more efficient to select a two-pole (3,600 rpm) or a four-pole (1,800 rpm) motor? How much more?

What if the conditions change to 2,000 gpm and 200 ft of head? Would your answer be the same for the motor speed? Would a VFD help?

Give it your best! The best answer gets you a winning ticket to the upcoming PumpTec-2009 in Atlanta:

Pumps & Systems, September 2009