WATER SUPPLY · PUMP DUTY POINT
Wildfire Water Pump Sizing Calculator
Estimate the flow and pressure duty a pump must meet after elevation, hose friction, fittings and nozzle pressure are included. Compare the hydraulic requirement with the manufacturer’s real pump curve.
TARGET PUMP DUTY
At 46.0 L/min design flow
A pump’s advertised maximum flow and maximum head do not occur simultaneously. Its curve must pass above both calculated coordinates.
THE SYSTEM CURVE
Flow costs pressure.
Small increases in flow can sharply increase friction loss. Internal diameter has an even stronger influence, which is why nominal hose size and actual inside diameter should not be confused.
hf = 10.67 LQ1.852 ÷ (C1.852d4.87)TDH = static lift + pressure head + adjusted frictionPhyd = ρgQ × TDHAdd flows
Total simultaneous outlet demand plus the selected design margin.
Lose pressure
Hazen–Williams estimates straight-pipe friction; fittings allowance increases it.
Add head
Elevation, required terminal pressure and friction form total dynamic head.
Check curve
Select equipment from its continuous-duty curve, not maximum headline values.
WHAT THE NUMBER MISSES
The pump is only one link.
Suction lift, priming, inlet restrictions, water temperature, altitude, voltage drop, starting current and debris can reduce performance. Flexible hose may also have a different internal diameter and loss behaviour from smooth pipe.
Required field checks
- Manufacturer curve at calculated flow and head
- Maximum suction lift and priming method
- Continuous-duty rating and cooling
- Filter, valve and connector losses
- Available electrical starting power
- Measured pressure at the furthest outlet
Sources and limitations
The metric Hazen–Williams equation is used as a screening estimate for water flow in a single representative hose/pipe run. It is empirical and does not replace detailed hydraulic design or equipment testing.
US Bureau of Reclamation: Hazen–Williams use · US DOE: pump-system calculations · CAL FIRE: evacuation guidance
Quick answers
Can I choose a pump from watts alone?
No. Required flow and total dynamic head define the duty point; power is a secondary estimate.
Why is inside diameter so important?
Friction in this equation varies approximately with diameter to the power of 4.87.
Does the calculator include suction-side loss?
Only if you include that length and diameter as a representative equivalent run. Complex suction systems require separate analysis.