When does it make sense to use booster pumps for a house water supply?

Booster pumps help to save valuable drinking water. Pumps draw in process water or rainwater stored in tanks or cisterns and supply it for, e.g. WC flushing, washing machines, garden watering or cleaning. A separate pipeline must be installed for process water. Daily drinking water requirements can be reduced by up to 60%.

FAQ – General questions

What is the difference between garden pumps, booster pumps with pressure tank, and electronic booster pumps?

All three types of pump are deployed when process water is used in private households. They draw in water and deliver it under pressure. Operating pressures are of the same order as a typical house water supply.

Garden pumps are mobile and are used outdoors for watering gardens and cleaning. Garden pumps have to be switched off manually if no water is drawn in for several minutes. They can be retrofitted with additional control devices to make them switch off automatically.

Electronic booster pumps and booster pumps with a pressure tank are usually installed indoors to enable process water to be used for WC flushing, washing machines or cleaning. They are connected to a separate, dedicated system of pipes.

Electronic booster pumps and booster pumps with a pressure tank cut out automatically when the water outlet is turned off.

Booster pumps with pressure tanks have a pressurised tank. The tank works as a puffer storage. The pump is not switching on and off repeatedly when small amounts of water are used (e.g. for flushing toilets, washing machines, etc.).

Electronic booster pumps are more compact and can be used outdoors as garden pumps. They are especially suitable for use when water is drawn for extended periods and constantly high pressure is required (e.g. for watering with a sprinkler).

Can a booster pump be used to increase the pressure where water pressure is low?

If Kärcher booster pumps are used to increase pressure, the feed pressure must not be higher than 1 bar.

NB: If the feed pressure is greater than 1 bar, the pumps do not switch on automatically.

What is a self-priming pump?

A self-priming pump is a pump that can draw water automatically from a water extraction point via an empty suction pipe. The maximum suction hight is 8 m.

On initial start-up the pump head must be filled with water, since the pump cannot generate vacuum in an empty pump chamber.

It is helpful to fill the connected suction hose with water. This shortens the intake time.

To prevent water that has been drawn in from flowing back again and to avoid having to repeat the intake procedure, we recommend fitting a check valve (foot valve) to the water intake side of the suction hose. When the pump is re-started it begins drawing in water immediately and delivering it to the water outlet point. The complete suction set is available as a Kärcher accessory.

Is it important to use a prefilter?

To ensure problem-free operation when water is drawn off, prefilters are used. Otherwise, given the small diameters of some water taps, washing machine pipes, WC cistern valves, sprinkler and spray nozzles, blockages may occur. Kärcher booster pumps have an integrated prefilter with a 500µm mesh gauge as standard. If the water is especially dirty or sandy, we recommend using an additional pump prefilter (Kärcher accessory number, up to 3,000 l/hour 6.997-343 or up to 6000 l/h
6.997-344.0). This has a 250µm mesh gauge.

How does a dry run cut-out work?

The dry run cut-out is fitted into the water pipe on the pressure side. It is plugged into a standard electrical socket and has an integrated socket for connecting the pump. When a lack of water is identified the dry run cut-out interrupts the power supply to the pump.

Why is it necessary to use a check valve?

A check valve prevents the return flow of water that has been drawn in. It is helpful when priming the pump, when starting up, or if air is trapped in the pipes.

A distinction is drawn between two check valves: a stop valve on the suction pipe strainer, and a check valve on the suction side entrance to the pump or integrated into the pump on the suction side. This check valve maintains the pipeline pressure after the pump has shut down automatically.

On which water pipes is a Kärcher booster pump installed?

Kärcher booster pumps are designed to pump process water. They must not be connected to the drinking water supply.

How is pump output (pressure, flow rate) distributed when several taps are turned on simultaneously?

The water pressure drops when water is drawn at several points simultaneously. However, Kärcher booster pumps deliver a sufficient performance for normal use in private households (e.g. water tap, WC flush or washing machine).

What happens when the water reservoir (cistern) runs dry and the booster pump is not drawing in any more water?

The booster pump electronic (BPE) has an integrated dry run cut-out which would switch off the pump.

In the case of the booster pump with pressure tank (BPP) a lack of water in the cistern can prevent the pump from building up pressure, so that it does not cut out. The resulting dry running can damage the pump.

However, a dry run cut-out can be retrofitted (Kärcher part number 6.997-355.0). It is also possible to use a float switch in the water reservoir to identify the lack of water and switch off the pump
(Kärcher accessory 6.997-356.0).

An alternative solution is to feed drinking water into the system automatically when the cistern is
dry, paying attention to strict separation of the media (process water / dinking water) . If you wish to do this, please consult a specialist craftsman.

Can the water in the pump cause damage such as corrosion if it is shut down for extended periods?

All components that come into contact with water are made of waterproof plastic or stainless steel, so continuous contact with water is not a cause for concern.

Is it necessary to unplug a booster pump during extended shutdowns or absences (e.g. on holiday)?

In case of extended absence (e.g. on holiday) we recommend unplugging booster pumps (especially the BPP models) in order to prevent damaging from dry running should a leak occur and the water reservoir run dry.