Ask the Expert Question-and-Answer Archive (Wastewater Treatment)
by Mike McGinness, EcoShield Environmental Systems, Inc.
Q. When you want to save money on energy costs. Do you throttle the suction or discharge valve down?
What's the most common Impeller on a Centrifugal Pump Open or Closed Impeller?
A. The answer is to throttle the suction if you want to save energy. But be carefull that you allow enough to air flow to cool the blower bearings! Check the manual for details on the minimum continuous air flow and maximum pressure. If you choke the flow too much the pumped air and bearings will overheat.
I am not sure that either one is really more common. I am told that the open impellers are better at handling solids, and the data I have seen indicates to me that closed impellers tend to be more energy efficient.