The different centrifugal impellers

How does an impeller work?

Almost all submersible pumps are centrifugal pumps. The motor spins an impeller with vanes. Water enters at the centre (the 'eye') and is flung outwards by centrifugal force towards the outlet. The shape of the impeller determines how much water the pump moves, how efficiently it does so and how large the solids carried along may be.

The impeller types at a glance

Channel impellers: open, semi-open and closed

Open impeller: the vanes are open on both sides. Simple and inexpensive, but less robust and more prone to cavitation. You mainly find it in smaller pumps for clean water.

Semi-open impeller: the vanes are reinforced with a plate at the back. A good balance between efficiency and tolerance of dirt. The clearance between the vanes and the pump housing must stay small, otherwise efficiency drops.

Closed impeller: the vanes sit between two plates. This gives the highest efficiency and pressure, but the narrow channels clog quickly. It is therefore mainly suited to clean water, as in borehole pumps.

Vortex impeller: the choice for dirty water

A vortex impeller is recessed in the pump housing. It creates a whirlpool that sets the water in motion, while most solids flow past the impeller rather than through it. As a result, it hardly ever clogs and suffers less wear from sand and sludge. The downside is lower efficiency: you need slightly more power for the same flow rate. Choose a vortex impeller if your water contains fibres, leaf debris, sludge or small solids.

Example: the Pentair U3K(S) and Simer 6 have a vortex impeller, which makes them insensitive to lightly contaminated water in a basement or pit.

Cutter: for toilet water and narrow pipes

A pump with a cutter has blades that grind solids finely before they enter the pump. This allows toilet water to pass through a discharge pipe just a few centimetres wide, which is handy for renovations and long pipe runs. A cutter does need some back pressure to work properly, and the blades have to be replaced over time. If you have room for a wide discharge pipe, a pump with a large free passage is often simpler.

Which pump goes with which impeller?

VORTEX – LIGHTLY CONTAMINATED

Pentair Jung U3K(S)

For basements and pump pits, with float switch and 10 m cable.

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VORTEX / SINGLE-CHANNEL – DIRTY WATER

HOMA TP48 (50 mm passage)

50 mm free passage for coarse dirty water, choice of impeller type.

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CUTTER – SEWAGE

Pentair UFK MultiCut 08/2 ME

MultiCut blades for sewage through a narrow discharge pipe.

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Also see the HOMA TP28 with 28 mm passage, or filter by impeller type in all submersible pumps.

Frequently asked questions

Which impeller is best for dirty water?

A vortex impeller. Most solids flow past the impeller, so the pump hardly ever clogs. For toilet water through a narrow pipe, choose a cutter.

What is the difference between a vortex and a channel impeller?

A channel impeller drives all the water through the vanes and has a higher efficiency, but clogs more easily. A vortex impeller works with a whirlpool; it is less efficient but far less sensitive to dirt.

When do I need a pump with a cutter?

When you need to pump toilet water or wastewater containing solids through a narrow discharge pipe, for example during a renovation or over a long pipe run.

What does free passage mean?

The largest diameter of a solid that can pass through the pump unhindered. The dirtier the water, the larger the free passage needs to be.