Tank to Pump

Hydraulics & Pressure

Back Pressure

Back pressure is pressure working against the pump, most often from lifting water to a higher elevation. It adds to the pump discharge pressure the operator must produce.

Elevation above the pump is the classic source of back pressure: the weight of the standing water column pushes back down the line. On a standpipe or high-rise stretch this can be the largest single term in the pump pressure.

Back pressure is the opposite of forward pressure from a downhill lay, which helps the pump. Reading the situation correctly — when elevation is fighting you versus helping you — is part of setting an accurate target.

Formula

Back pressure ≈ 0.5 × (height of the water column above the pump)

Training shortcut: about 0.5 psi for each foot of rise, or about 5 psi per floor. This is the same quantity as elevation pressure, viewed as the load fighting the pump.

Common questions

What is back pressure?
Back pressure is pressure working against the pump, most often the weight of a standing water column when you lift water to a higher elevation. It adds to the pump discharge pressure the operator has to produce.
What is the difference between back pressure and forward pressure?
Back pressure fights the pump when the nozzle is above it — uphill. Forward pressure helps the pump when the nozzle is below it — downhill, the standing column pushes the water along. Reading which one applies is part of setting an accurate target.

Where this shows up

See also