Pump head, power and efficiency
Total head, hydraulic and shaft power and pump efficiency from field readings — and what a worn pump costs a year.
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The Pump Head, Power and Efficiency Excel tool does everything here and more: head, efficiency and power curves for any impeller diameter and speed from the vendor's curves, the motor size with API 610 margins, low-flow alerts and a field test against the curve. Print-ready report, any units, visible formulas, no macros.
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How this calculator works
Total head = (discharge pressure − suction pressure) ÷ (ρ·g) + gauge height difference + (vd² − vs²) ÷ 2g. Hydraulic power = ρ·g·Q·H. Shaft power = motor input power × motor efficiency. Pump efficiency = hydraulic power ÷ shaft power; wire-to-water efficiency = hydraulic power ÷ motor input power.
If you enter the best efficiency from the maker's curve, the calculator shows the power the pump would draw at that efficiency, and the yearly saving from restoring it.
The example is a cooling water pump for the PlantCalcKit example tower: 6,000 m³/h, 0.5 to 2.9 bar g, 560 kW motor input. Total head 25.6 m, hydraulic power 418 kW, shaft power 535 kW, so the pump runs at 78 % against 86 % when new — about 51 kW, or USD 43,000 a year at USD 0.10/kWh.
Closed-loop heat: tick the checkbox to see how much heat the pump adds to a closed-loop system. In a closed loop every watt of shaft power ends up as heat in the fluid, because the hydraulic power just moves the fluid around the loop and pipe friction converts it all to thermal energy. If a control valve throttles the flow, its pressure drop adds more heat (Q × ΔP). Subtract this total from the cooler or heater duty when sizing the system.
Limits: for liquids (incompressible); viscous liquids need the maker's correction; motor efficiency taken as constant. References: Perry's Chemical Engineers' Handbook §10; Hydraulic Institute pump standards; Ludwig, Applied Process Design Vol. 1; GPSA Engineering Data Book Sec. 12.