Water pump in the motorhome

Reading time 3 minutes

The water pump in the motorhome usually does its job quite inconspicuously, albeit more or less audibly.

Only when it stops pumping water one day, but the fuse in the vehicle's manual is in order, do two questions arise: where is it installed and which one is it?

What types of pumps are there?

Smaller water tanks usually house a gear pump, which is located on the bottom of the water tank as a submersible pump. The delivery hose and connection cable are usually routed through the screw cap lid of the tank via two holes with watertight feedthroughs.
Taps designed for such pumps have a built-in or attached microswitch that switches the power supply to the pump when the tap is opened, whereupon a fairly bright buzzing sound is emitted and the water starts to flow.

In the case of larger tanks, pressure pumps are installed due to several tapping points and the resulting requirements for larger flow rates, which optionally have a filter downstream at the outlet to protect against coarser impurities in the form of a screen filter that needs to be cleaned from time to time.
Water taps for pressure pumps are conventional household water taps that are designed for mobile use in a predominantly lighter design. When the tap is opened, water immediately flows at a higher pressure than with the aforementioned gear pumps. After a corresponding drop in pressure, an often rattling sound is heard, which indicates the continuous build-up of pressure for a consistently high water flow rate.

The pump noise alone indicates the type of pump installed.

Advantages - disadvantages of the types

The advantages and disadvantages are relative. The small gear (submersible) pumps tend to require less power, pump less pressure but possibly more water, are more susceptible than their larger counterparts, the pressure pumps, but only cost around 20 ... 50 euros.
So if you want to get by with little power (consumption approx. 2 A (approx. 10 liters/min. at 0.85 bar) ... 7 A (approx. 25 l/min. at 2.1 bar)) and only have one or two taps that are rarely used at the same time and do not have a water tank larger than approx. 100 liters, the small pump is a good choice.

If electricity is not important, but high pressure for parallel water withdrawal at different taps is preferred, then the pressure pump with 2.4 A (approx. 4.9 ltr./min. at 2.1 bar) ... 11.8 A (approx. 18.9 ltr./min. at 2.8 bar) is the right choice. They are available for around 90 ... 240 euros, depending on the manufacturer, application (recreational vehicle, marine) and, if applicable, electronic instead of electromechanical control.

However, the power consumption may be relativized: while the gear pump runs during the entire water withdrawal, the pressure pump only consumes power intermittently.

The achievable throughput is of course also dependent on the available hose diameter.

By the way: you are always well advised to have a spare pump (of the same type) on board! According to Murphy's law, the pump will always go on strike when there is no spare available, it's the weekend and you're ideally in the middle of nowhere ...
If the design or hose connections differ, the required adapters should also be procured in advance so that all the necessary components can be replaced if necessary!

Replacement in the event of a defect

Gear (submersible) pump

Replacing a pump of the same design(!) is not particularly difficult and can be done quickly. If the design does not match, but the cable and hose diameter are suitable, as is the maximum pump diameter for inserting it through the tank opening into the water tank, the job is also done quickly: remove the old pump, disconnect the hose, cut the cable outside the tank, connect the new pump to the hose, bring its cable through the cable gland outside the tank and connect it with the correct polarity. Done!

It only becomes critical if the existing conditions do not correlate with those of the replacement pump, e.g. if a different cable or hose feed-through has to be created.
Drills and power drills are never far away at home, but rarely on board when out and about.

Pressure pump

Replacing a pressure pump is somewhat more complicated. It is usually installed near the water tank in the intermediate floor and is rarely easily accessible. In addition, almost without exception there is no (!) shut-off valve between the water tank and the pump, which means that it has to be completely emptied. Unless you have taken precautions and installed a shut-off device, possibly at a later date.

There is also rarely a shut-off on the outlet side, so residual water will find its way unwelcome into the false floor when the hose is removed, unless it is effectively disconnected.
So here, too, you should have made provisions.

Once these hurdles have been overcome, the connections can be disconnected, both electrically and mechanically, the pump can be detached from the floor by its brackets, replaced with the new one, screwed tight, the hose connections restored and the power supply reconnected.

Safety precautions

As the pressure pump will continue to pump until no more water is available in the event of a pressure loss, there is a risk that a hose leak will involuntarily turn your camper van floor into at least one extended footbath.

It is therefore helpful to have a centrally accessible switch with indicator light in the positive or negative line of the pressure pump, which allows you to switch it off when you are absent or at night, thus preventing the aforementioned inconvenience. If this is not already provided by the manufacturer, it should be retrofitted.

If you use SmartHome, you can use a programmatically controlled relay contact via geofencing to detect absence and switch the pump off or on at defined times at night.