Now let’s take a look at how to adjust the various types of the most popular pressure switches found in caravans. Whale in-line pressure switch Whale in-line pressure switch might be hidden in pipework

Dusty's suggestion of a surge damper may work, but its not actually designed to prevent your specific problem. You might find another pump may not exhibit the same oscillation. Even pumps of the same model will have slight differences in performance which might be just enough to prevent your problem. Whale In-Line Pressure Switch WU7207. Convenient way to install a pressure on a demand system in caravan or motorhome. It is recommended that a surge damper, is fitted in conjunction with Whale Elegance, Elite & TB faucets. Hose bore:12mm (1/2") Being submerged, these pumps do not need priming (filling with water first) and most are self-venting, so any air trapped inside can escape through a hole in the top. If not, then shaking the submerged pump for a few seconds can help.After a few hours of playing with the system today adjusting the pressure switch screw to no avail and now thinking about it I will try some silicon around the external pumps connecting nozzle seals as you suggested - will try this on Sunday. This seems to be the only point that air could entre the system causing a pressure drop thus pump runs continuous. But the system / boiler all work fine apart from the pump running continually, with only a small amount of spluttering at the taps after the main control panel was switched off for about 5 mins. Another is the Shurflo . Swift used to fit this make before switching to Flojet. Whale also makes diaphragm pumps.

The first to market with a combined water and space heater for touring use was Alde, as long ago as 1966. The unit used antifreeze to heat both water and radiatorsand became renowned for its efficiency.

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So what is the cause of the oscillating water pressure, and having thought a bit more about it its better described as water hammer, where a mass of water is moving in a pipe and its inertia causes a pressure differential at either end of the pipe. The pipe has some compliance, and so the slug of water has some freedom to move like a piston in a cylinder. As with the other units, on occasion, I have had to repeat the process to get it right; but generally, once it’s been done, that’s it. Here is a simple pressure-switched system using a submersible pump. The pressure switch acts as a one-way valve keeping thepressure in the system when the pump switches off. The other one-way valve prevents warm water from the heater getting into the cold supply. This arrangement can be found on many Lunar caravans. The software within the device recognises exactly what the pump is doing at any one time. As the people at Whale also make the pumps they can do this very accurately. Even so, there can be slight differences between individual pumps and so there is a simple ‘one off’ calibration procedureif needed. With fitted on-board tanks, water systems can become quite complex. This is one of the simpler arrangements. The selector chooses between the two water sources, the isolator opens to fill the on-board the tank. The downside is that you have to manually operate the valves to fill and then use the on-board tank.