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Pump Discharge Pressure (PDP) Calculator

Calculate fire engine pump discharge pressure: nozzle pressure plus hose friction loss, appliance loss and elevation gain or loss for attack lines, standpipes and master streams, with nozzle flow from nozzle type and a breakdown of each term.

Nozzle

Nozzle flow

Attack hose diameter

Attack hose length

Supply / lead-out hose to a wye or standpipe (optional)

Supply hose length

Appliances

Storeys above the pump (negative = below)

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How it works

PDP = NP + FL(attack) + FL(supply) + appliance loss ± elevation (5 psi per storey, 0.434 psi/ft); FL = C Q² L

The pump operator must supply exactly the pressure the nozzle is designed for — 100 psi for a standard fog nozzle, 50 psi for a smooth-bore handline, 80 psi for a smooth-bore master stream — after the water has lost pressure to hose friction, to appliances such as wyes and standpipes, and to gravity on its way up the building. Too little and the stream is weak and the pattern collapses; too much and the nozzle reaction becomes uncontrollable and the hose can burst. The method is additive and intentionally simple enough to do on the pump panel: nozzle pressure, plus friction loss per hundred feet times the lay, plus 10 psi for an appliance, plus 5 psi per storey.

Worked example

A 100 psi fog nozzle flowing 150 gpm through 200 ft of 1¾″ (70 psi of friction loss) to the third floor (15 psi) with no appliances needs a pump discharge pressure of 185 psi. Switching to a 50 psi low-pressure nozzle drops it to 135 psi and halves the nozzle reaction.

Frequently asked questions

How much is elevation, exactly?

0.434 psi per vertical foot; departments round to 5 psi per storey above the first (some count every floor, some 10 ft = 5 psi). A hose running downhill gains pressure, so subtract it.

What about 2½″ handlines?

At 250–265 gpm through 2½″ the friction loss is only 12–14 psi per 100 ft, so PDP is often 150–170 psi with a smooth-bore tip — the reason the big line is preferred for large fires and long stretches.

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