Question 1

What is the difference between hydraulic, shaft and electrical power?

Accepted Answer

Hydraulic power is what reaches the fluid: ρ·g·Q·H. Shaft power is the mechanical input at the pump coupling and is larger, because pump efficiency is below 100%. Electrical input is larger again, because the motor and any drive have their own losses. The gaps between the three are exactly where energy is being spent.

Question 2

Should I enter total dynamic head directly or build it from the system?

Accepted Answer

Enter it directly when you already know the duty point — from a pump curve, a commissioning record or a specification. Build it from the system when you are sizing: the calculator then adds static lift to pipe friction and fitting losses to arrive at the head the pump must actually generate.

Question 3

How is pipe friction estimated?

Accepted Answer

Using the Hazen-Williams relation with a roughness coefficient C for the pipe material, plus minor losses entered as an equivalent fitting count. Hazen-Williams is intended for water at ordinary temperatures in full, turbulent flow; for other fluids, viscous flow or compressible service a Darcy-Weisbach approach is the correct method.

Question 4

Why derive efficiency from measured power instead of assuming it?

Accepted Answer

An assumed efficiency tells you what a pump should draw. Measured power tells you what it does draw. Comparing the two is how worn impellers, throttled valves, wrong-speed operation and oversized pumps are found — a pump running well away from its best efficiency point can easily cost double the energy the duty needs.

Question 5

What is wire-to-water efficiency?

Accepted Answer

The overall efficiency from electrical supply to delivered fluid power — pump efficiency multiplied by motor and drive efficiency. It is the figure that matters for energy cost, because it captures every loss between the meter and the water.

Question 6

What efficiency should I expect?

Accepted Answer

General-purpose centrifugal pumps typically run 60-85% at their best efficiency point, falling away sharply either side of it. Motors of a few kW and above are usually 90-95%. A wire-to-water figure much below 55% on a well-selected duty usually points at a selection or control problem rather than a worn pump.

Question 7

Does this replace the manufacturer's pump curve?

Accepted Answer

No. It is a screening and energy-check tool. Final selection needs the actual curve, NPSH available against NPSH required, the system curve across the operating range, and the fluid's real properties.

Pump Efficiency Calculator

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