I think it is useful to consider the aspects of 'power' separately:
the power to run the pump motor, and
the work input to the fluid
an illustration is the recirculation pump in my chiller,
a Pabst motor with a 10" shaft to the pump head in the chilled bath
- obviously no motor heat is being input into the fluid
with submerged pumps this is quite different, and to a lesser degree also with close coupled pumps
some pump specs list the 2 power values separately; power consumed by the motor (a maximum value), and work done by the pump
max flow = max power consumption (by the motor of course)
note that in a closed loop the NPSH will be rather high
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