Onboard water pumps

This discussion applies to older caravans with an onboard water tank, motorhomes, and many boats. Those involved have a small pump to fill the onboard tank, and a larger diaphragm pump inside to serve the systems.

Our Whale diaphragm pump started leaking after only 20 (yes, twenty) years. The current replacement has output of 8 litre/min compared with the old one 6 l/min. Great, I thought, power shower no less. But the new pump cycled every few seconds, causing the shower to blast cold and scalding alternately.

I called the very helpful folk at Whale who told me that this can be a common problem. The older narrow-bore pipes cannot take the increased flow, causing the pump to cycle. This also happens when someone upgrades to a higher-output pump thinking it will be a better job.

The solution is to fit the Whale surge damper, simply an air reservoir which damps out the pressure variations. We were baffled when the pump still cycled. Our problem was the water-saving trigger mechanism on the shower head, which acted as a restrictor. Once removed, the system is better than new.

Only problem is that our nice high-pressure shower means extra trips with the Aquaroll!