Calculating Power of a Water Pump: Enthalpy vs Pressure Difference

[Benjamin Crump]

Trying to calculate the power of a pump, it's pumping water.

It has a flowrate in and out in kg/s. Surely I should look up the enthalpy values and just mutiply with the flow rate to get power in kW.
However I know that if I convert flowrate to m3/s by dividing 1000 and multiplying by the pressure difference would I not be doing an energy balance? I get a different answer in both methods, which one is the valid method here?

 

[BvU]

Hello Ben,

Is the difference you get really that shocking ?

There's a calculator here to compare your results

 

[OldYat47]

What kind of pump? If it's a centrifugal then you must know the efficiency at the particular pumping rate and differential pressure. If it's positive displacement of some sort then friction of the mechanical elements enters into the equation. There are too many unknowns in your question as stated.