Fire pump selection is not simply choosing a flow and pressure point from a catalogue. The correct duty must be derived from the design scenario, network arrangement, elevations, path losses and required pressure at the most remote demand point.
1. Identify the governing scenario
First determine which simultaneous demand governs: sprinklers, hydrants, fire boxes, monitors or a water–foam system. Adding every demand without scenario logic usually oversizes the pump, while omitting a real concurrent demand creates an unsafe design.
2. Break down required head
Pipe pressure rating does not replace hydraulic calculation. PN or Class only indicates pressure capacity; the pump duty point must come from the critical-path calculation.
3. Check suction conditions and NPSH
For a buried tank, pump centreline elevation relative to minimum water level, suction-line losses and air-pocket risks are critical. Available NPSH must be compared with the manufacturer's required NPSH using an appropriate margin.
4. Review the entire pump curve
The rated point alone is not enough. Review shutoff pressure, performance at rated and 150% flow, motor power and maximum network pressure.