Booster pumps get chosen on flow rate alone and then underperform. Flow is only half the specification — head is the half that gets skipped.
Head and flow, together
Flow rate is how much water moves per minute. Head is how much pressure the pump can generate, expressed as the vertical height of water it can lift.
A pump rated for plenty of flow at zero head can deliver almost nothing once it has to push water up three storeys and along a run of pipe. Every pump has a curve: as head goes up, flow comes down. The rated figures on the box are the best case, not your case.
Work out the head you actually need
Three things add up:
- Static head — the vertical distance from water level to the highest outlet.
- Friction loss — resistance from pipe length, diameter, bends and fittings. Long or narrow pipe runs add up faster than people expect.
- Required outlet pressure — whatever the fixture or equipment at the end needs to work properly.
Add all three, then choose a pump that delivers your target flow at that total head — not at its headline rating.
The most common mistake
Undersizing head. It is the single most frequent reason a booster pump disappoints after installation. The pump runs, water arrives, but pressure at the far outlet is weak and nobody can explain why.
Second most common: oversizing flow. An oversized pump short-cycles, wears its switchgear and costs more to run.
Fixed speed or VSD?
- Fixed speed — simpler and cheaper. Fine for steady, predictable demand.
- Variable speed (VSD) — matches output to demand, holds pressure steady as taps open and close, uses less energy and reduces cycling. Worth it where demand varies through the day.
Pairing with storage
A booster pump and a tank are usually specified together. The tank buffers supply interruptions; the pump delivers usable pressure. Size the tank to how long you need to ride through an outage, and the pump to peak demand — not average.
Spec checklist
- Peak flow demand, not average
- Total head: static + friction + required outlet pressure
- Performance confirmed at your duty point, not the headline rating
- Fixed speed or VSD based on how variable demand really is
- Tank sized to the outage you need to survive
- Power available at the installation point
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Send us the head, flow and site conditions and we will confirm the duty point before you order. Get in touch.