Wattage consumption

Centrifugal pumps are affected by something called the "Laws of Affinity" and are different from positive displacement pumps and other devices. I stand by my original statement.

 

I've done the research and you are correct: minimum power at shut-off head...

...though not zero power, which is what I was thinking you were saying but you weren't...

;D

 

Shut off head is whn it is no longer moving water due to a closed valve or maximum height. 0' head is when it is pumping the maximum amount of water possible, two different scenarios. At shut off head the power consumption is usually at its lowest since little to no work is being performed, at 0' head its at its highest as it is doing maximum work moving water.

 

Like you said, not zero energy, just lowest wattage.

A centrifical pump can only "fling" fluid so hard or so high. After that it simply slips and spins in the working fluid. Power is being consumed just by losses I mentioned earlier, but no water is moving. Opening the valve or lowering the head will cause water to move, more work to be done, power consumption to increase.