Pump Head Calculator

Static lift plus friction head — the total resistance a pump works against. Static lift alone is what a drawing shows, and it is never the whole figure.

From a friction chart for the pipe bore and flow rate, applied to the equivalent length — actual pipe plus an allowance for fittings, since a bend or valve behaves like several metres of straight pipe.

Because the rating is at zero flow. Every pump has a curve where delivered head falls as flow rises, so the useful operating point is well below the maximum head printed on the box.

Hydraulic power is density times gravity times flow times head; shaft power is that divided by efficiency. A pump at 60% efficiency draws two-thirds more than the water actually requires.

Vapour bubbles forming at the suction side when pressure drops too low, then collapsing violently and eroding the impeller. It sounds like gravel in the pump and it destroys it quickly.

Roughly with its square, which is why a pump that copes at low demand can fail at full flow. It is the most common reason a system works when tested and fails in use.

Net positive suction head — the pressure available at the pump inlet above the vapour pressure of the liquid. Too little and the pump cavitates, which destroys the impeller quickly.

Head on the vertical axis against flow on the horizontal. Your system's operating point is where the curve crosses the system resistance, and the efficiency is usually plotted alongside.

Not much. An oversized pump runs off its best efficiency point, wastes energy and can cause water hammer and premature wear. Matching the duty point is what matters.

Where demand varies, a great deal — power goes roughly with the cube of speed, so running at 80% speed uses about half the energy. Pool and heating circulation are the classic cases.

Air entering the suction line, usually through a leaking joint or a suction lift that is too high. A foot valve at the intake is the standard remedy.

Under about 8 metres in practice, because atmospheric pressure is what pushes the water up and losses reduce the theoretical 10.3 metres. Deeper lifts need a submersible or a jet pump.