water pump battery /mains

[Richard_374305805]

the carver water pump on my Lunar Quasar 544 2015 works fine on mains but on a fully charged battery only, it carries on running for ever after the taps have been turned off. This can be corrected by adjusting the pressure regulator and my question is should it need to be.
If the pressure regulator is set for correct operation on the battery then I'm getting lower pressure water that I could be when returning to mains. Also the pressure regulator has to be continually adjusted as the battery voltage drops if I'm on battery only, for a couple of days. The worst is if I don't spot the pump is not switching off then it continues to run until the battery is flat which takes about 5 hours, which is kind of annoying when you've gone out for the day from a CL with no mains.
The main dealer gave the impression that that was the way it was and there is no fault, I'm not so sure.

 

[WoodlandsCamper]

We switch our pump off when we go out for the day, and also overnight so we don't get woken up by the odd cut-in as things cool down.

 

[VicMallows]

Your symptoms suggest to me that your pump is simply not able to develop enough pressure at anything less than maximum voltage. Most probably due to a worn impeller. Is it a stand-alone pump you put into an aqua-roll ....or a built-in pump?

 

[timhowarduk]

For similar reasons, I fitted a Halfords illuminated red rocker switch which totally isolates the pump, and glows red when the pump is running. If you can't hear the pump from inside the van then maybe adding a warning lamp would help matters?

 

[ProfJohnL]

Your symptoms suggest to me that your pump is simply not able to develop enough pressure at anything less than maximum voltage. Most probably due to a worn impeller. Is it a stand-alone pump you put into an aqua-roll ....or a built-in pump?

Carver only sold submersible pumps.

And it is far from unusual to have to readjust the pressure switch setting as the supply voltage changes.

 

[Richard_374305805]

Thanks Prof - I did wonder if it was more common place to have to adjust the regulator, I've never had to do it with the 2 vans I've owned over 20 odd years, but then the first of those had micro switches on the taps so you didn't have this problem, but they frequently failed and boy where they a pain to change.

 

[VicMallows]

And it is far from unusual to have to readjust the pressure switch setting as the supply voltage changes.

Why would that be? The pressure switch is a mechanical device which switches at a set pressure .... whether or not an electrical supply is present. You appear to be confirming what I said: that at lower voltage the pump is incapable of developing the pressure needed to operate the pressure switch. Yes of course you can reduce the pressure setting, and if that suits your needs then just leave it at that setting.

 

[WoodlandsCamper]

On a previous van I replaced the 2-wire pressure switch with a 3-wire voltage compensating switch and it worked a treat. Unfortunately they are no longer available, I believe the design was bought by one of the conglomerates and they don't manufacture it because it affects the sale of 'other' components.

 

[ProfJohnL]

And it is far from unusual to have to readjust the pressure switch setting as the supply voltage changes.

Why would that be? The pressure switch is a mechanical device which switches at a set pressure .... whether or not an electrical supply is present. You appear to be confirming what I said: that at lower voltage the pump is incapable of developing the pressure needed to operate the pressure switch. Yes of course you can reduce the pressure setting, and if that suits your needs then just leave it at that setting.

Hello Vic,
That is exactly it, you may need to adjust the pressure switch to suit the supply voltage. This is not uncommon.

Yes you could leave it set at the lower pressure, but as usual its a compromise.

See
https://www.youtube.com/watch?v=CUbfuxl3R_o

Using the method recommended by Whale, the setting will only work as described for a modest range of supply voltages.

Lets consider what will happen if the supply voltage is lowered, becasue the pump impeller will be turning slower, it will develop less pressure, ultimately the pump will not produce enough pressure to trip the switch, resulting is the pump continuing to run.

Now consider what happens if the voltage is increased. The pump will run faster, and this will have several effect:
The rate of pressure rise in the pipe work will be faster,
The pressure overshoot will be greater.
The combined effect will be the pump will start to turn off and on (hunting) whilst the tap is open.

For separate hot and cold taps, this may not a major problem, but if the system is feeding a mixer tap, then the problem is different. Inside the mixer tap the hot and cold water flows are mixed in a chamber before they emerge from the tap. This mixing chamber has teh effect of allowing pressures in both hot and cold systems to be equalised. As long as both hot and cold systems are delivering water at the same pressure both will flow, but if either system is raised relative to the other will inhibit the flow from the lower pressure system.

The problem arises becasue the hot water tanks have a designed expansion air cap to allow cold water to expand as its heated, but it also has a secondary effect of acting as a pressure accumulator. As the pump runs it will pressurise both cold and hot circuits, but when the pressure switch trips, the air cap maintains a high pressure and will preferentially continue to deliver water from the hot tank, even though the cold flow has stopped, This delivers alternating mixed warm and just hot water.

 

[VicMallows]

So you are telling me that caravans with pressurised systems do not also include a suitably sized accumulator vessel in the pressurised cold supply? .... surprise, surprise!. (It is standard practice in boats for precisely the reasons you cite).

The shower in our 'van has separate hot/cold taps. One of the first things I did was to fit a decent separate thermostatic mixer valve. Now you simply turn on the hot tap if you want a consistent hot shower at the correct temperature. If you want a cold shower you turn on the cold tap!

 

[ProfJohnL]

So you are telling me that caravans with pressurised systems do not also include a suitably sized accumulator vessel in the pressurised cold supply? .... surprise, surprise!. (It is standard practice in boats for precisely the reasons you cite).

The shower in our 'van has separate hot/cold taps. One of the first things I did was to fit a decent separate thermostatic mixer valve. Now you simply turn on the hot tap if you want a consistent hot shower at the correct temperature. If you want a cold shower you turn on the cold tap!

Got it in one!