Tap pressure switch

[thedoog1]

We are currently away in our van, and the pump pressure switch is playing up. Unfortunately the caravan manuals are sat at home. Can anyone sdvise on the method of adjustment at the moment the pump runs constantly so we are having to turn the pump off on the master switch.

Steve

 

[Woodentop]

There be a knob on the pressure switch between the pump and the system. Turn the knob until the pump stops, then micro-adjust it such that it starts when you turn the tap on and stops a few seconds after you turn it off - long enough to pressurise the system.

 

[thedoog1]

Silly question clockwise or anticlockwise?

 

[WoodlandsCamper]

I think you have to screw it in clockwise to switch it off, but if that doesn't work try the other way.

 

[thedoog1]

Well it appears to be anticlockwise it now switches off. But on past performance I wonder how long it will continue working. I will most definateley be mentioning this when it goes in for its first service next month.

 

[WoodlandsCamper]

The pressure switches are very sensitive to the battery voltage. If you are off-grid and the battery voltage level is dropping then that may explain it. On our previous van (an old Avondale) I retro-fitted a switch bought on the internet which had 3 wires instead of 2 and compensated for voltage drop. It was a brilliant item and worked very well, but unfortunately the supplier stopped supplying it.

 

[thedoog1]

No we are on hookup,the switch has been a pain most f the time.

 

[chrisn7]

WC has largely covered this which I guess is a Whale type. I never found the switch to be voltage sensitive, except when changing between 12v and 230v when it had to be re-adjusted each time.
The correct process is to turn the wheel fully clockwise (as in turning off a tap), as far as it go, then turn back anti clock until the pump stops, followed by a further half turn. This gives a datum point from which you might have adjust either way very slightly. Once set for a given voltage, it should be stable.

They do have one advantage: if the pump is heard to kick in when you think all taps are off, then either one isn't, or a leak has developed somewhere, especially if it starts, runs briefly, then stays off for quite a while, then repeats.

 

[bertieboy1]

Switches such as the one described are not voltage sensitive,they only switch a voltage on or off without actually using any power to do so.

 

[ProfJohnL]

Switches such as the one described are not voltage sensitive,they only switch a voltage on or off without actually using any power to do so.

Hello Bertie,

Technically you are correct, but there is often a difference in the the way the pressure switch appears to operate when on EHU or just battery. Its not the switch, but the performance of the pump which is affected by the actual voltage on the 12V system. and the elasticity of the plastic pipes and the air cap in the water heater.

When the pump operates it raises the pressure in the water pipes, and when the taps are closed the pump continues until it raises the pressure towards the trip point of the pressure switch. As there is no water flow ( the taps are closed) all the pump is doing is raising the pressure. Even though the amount if inertia of the pumps impeller is quite small, it cannot stop instantly, so even when the switch kills the power the impeller raises the pressure beyond the trip point by an amount. How much depends on how fast it was turning when the power was switched off. The greater the voltage the faster its runs.

The extra pressure is absorbed by the air cap in the water heater and the elasticity of the plastic water pipes. This elasticity maintains the pressure in the pipework, but if its not been stretched quite as much, the pipes return to their relaxed state and the pressure drops which can be enough to turn the pump on again.

Consequently some caravanners find they need to readjust the pressure switch setting each time they switch between battery and EHU power.