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post #1 of 12 (permalink) Old 06-08-2012, 21:28 Thread Starter
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left water pump running dry

After a sat night away i drained down the water tank, went home emptied the few bits out of the van, then locked up. this evening (mon) wife was in the van and heard the pump surging and shouts whats that noise, i switched the pump off at the panel left it while and filled the tank and tested if it would still pump and all seems ok. Not had the the van long so still learning about the systems in it. the pump is a posiflow 3000-151-2201. and the van is a autocruise pioneer renior.
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post #2 of 12 (permalink) Old 06-08-2012, 21:39
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Obviously it's not good to leave the water pump running dry (this can only happen if the pump is calling for water, i.e. a tap has been left open). You seem to have been lucky this time.
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post #3 of 12 (permalink) Old 06-08-2012, 23:09
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I don't know about your pump, but ours is a very common type.
It is basically an electric motor rotating a cam which causes a rubber membrane to flex. A pair of rubber discs serve as one-way valves.
The presence or absence of water would not have any effect on any of these.
I think the worst would come from over heating but that would take some considerable time.

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post #4 of 12 (permalink) Old 07-08-2012, 07:01
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This is the only info I found

This is all I found

If it's a diaphram pump, all may be fine, just fill the system and give the pump chance to dispel all the air and it might work OK.

Our Shurflo was left on the 3 months, and the solar panel kept it going, I re-filled expecting the worst, bu tit was just like before.

Shurflo actually say on the box that they can run dry with no problems, so if you have to replace a Shurflo trailking 7 20/30psi pump is less than £50, search using "supaprice" only get the highest PSI your water boiler will handle.

Kev.
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post #5 of 12 (permalink) Old 07-08-2012, 08:50
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Most now work on a pressure drop so if there is no water in the system it should be off.
Steve
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post #6 of 12 (permalink) Old 07-08-2012, 09:31
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max123, that is totally wrong, with no water in the system the pressure switch will "see" no pressure and activate the pump motor, which will run until the switch "sees" it's shut off pressure.
So no water it will run continuously.
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post #7 of 12 (permalink) Old 07-08-2012, 10:13
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I always thought they worked like a shower pump, ie. a magnetic float and reed relay, so when the tap is turned on there is a pressure difference ans the pump Is switched on. You are probably correct and as I can't be arsed to go outside and look at my system I will take your word for it.
Steve
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post #8 of 12 (permalink) Old 07-08-2012, 10:55
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Steve, there are two basic types of motorhome systems in use nowadays.
Switched and pressure differential, on the switched system (common on Hymers) the taps have an electrical switch that actually turns pump on and off.
There are a few different types of presure pump, most work using the same principal of a water pressure activated switch that turns pump on when no or low pressure present and off when the operating pressure is achieved, on most pumps the switch is incorporated within the pump.

John
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post #9 of 12 (permalink) Old 27-09-2021, 20:43
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This was a problem I knew about, but still fell into the trap.

I turned off the electrics and drained the system (including leaving the taps open) ready for the winter. The next day, my son went into the motorhome and turned on the electrics. Obviously the pressure switch started demanding and the pump ran. My son did not notice the noise and then left the electrics on when he exited the motorhome. Luckily I spotted it the next morning (and the pump is still ok).

Is there a standard solution to avoid this problem (and why is it not fitted at manufacture)? I have a Hymer CC684. Maybe there is a hidden switch that I have not found yet!

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post #10 of 12 (permalink) Old 28-09-2021, 06:18
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No hidden switch that I am aware of, but it would be easy to fit a switch close to the pump to totally isolate it “just in case”, our control panel though has a water pump switch, just turning on the 12v does not turn on the water pump until that is pressed.

I do not know what control panel you have, but check that it does not exist on the control panel.

Alternatively, give your son a bill “just in case” that may well make him think (obviously I do not know if he is 4 or 40 but you get the picture 😁 ).
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