The pool pump: how it works

A centrifugal pump is a type of hydraulic pump that turns the mechanical energy of a rotating motor into the energy the water needs to move through the whole circuit. It is, quite literally, the heart of the system, without it, the filter, the salt chlorinator and everything else are useless, because there's no water circulating.

How water flows through it

Water enters through the centre of a rotating component called the impeller, which has small curved blades (vanes) that direct the fluid. Centrifugal force throws the water outward from the impeller, where the pump casing collects it, and thanks to the shape of that casing, it's channelled toward the outlet pipe, on its way to the filter.

The pump's 3 parts

• Pre-filter: the basket that traps leaves and large debris before it reaches the impeller, without it, any solid debris would damage the pump internally.
• Pump body: where the impeller sits, and through which water enters and exits (suction and discharge).
• Electric motor: responsible for delivering the energy the impeller needs to spin. In a few very specific installations it can be a combustion engine, though in domestic and community pools it's practically always electric.

Why it sometimes "loses its prime"

If the pump makes noise but barely moves water, the most common cause is an air leak on the suction side, before the pump itself. It could be a dried-out gasket on the pre-filter lid, a skimmer with the water level too low, or a leak at a fitting in that area. Because air is compressible, it stops the impeller from "gripping" the water with the force it needs.

Why the pre-filter matters so much

Checking and cleaning the pre-filter basket regularly isn't a nicety, it's what protects the pump's impeller from any solid debris that could damage it. A basket full of leaves also reduces flow, forcing the motor to work harder for the same result.

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