Water pump running occasionally - no obvious leak

[Giant]

We have a 12V Jabsco Par Max 2.9 water pump and a 5 litre accumulator tank, maintained at 15-25psi.

 

Every few hours the pump will run for 5 seconds or so. It's always done this.

 

A leak in the system is the obvious explanation but we've never been able to find any evidence of one. The water would have to end up in the bilges, but they're bone dry everywhere and always have been.

 

It's finally starting to drive me crazy. Is there any other explanation? My thought was that perhaps water was leaking from the high pressure side, back through the pump to the low pressure side, without leaving the system.

 

A couple of weeks ago we stripped and rebuilt the pump - it had started leaking out of the side of the pump housing. We cleaned everything up and refitted all the rubber seals and it's working fine again, but still runs occasionally just as it did before.

Edited June 25, 2015 by Giant

[Nickhlx]

If you have (or could put) a shut off valve on one side or the other of the pump (or both) it would illustrate which side of the pump the pressure is being lost (I assume the pressure switch is within the pump)

which would help narrow down the cause of the problem.

Nick

[Machpoint005]

Have you a flush toilet?

Is it just topping up after contraction in the calorifier tank?

[pete.i]

Mine used to do that until I fitted a non return valve in the feed pipe from the tank. Apparently the pressure was leaking back into the water storage tank and eventually the pump would activate for a few seconds. That cured my water pump activation

[Hoose]

Calorifier cooling will cause this also check the breather is clear on your water tank, ours blocked and caused this exact problem

[ditchcrawler]

I would suggest that if it only runs for 5 seconds your accumulator is not working correctly, if it was then a dip in pressure low enough to start the pump it run for several seconds to recharge the accumulator, unless you have something like a non return valve between the pump and the accumulator

[Machpoint005]

Is it just topping up after contraction in the calorifier tank?

 

 

Calorifier cooling will cause this

 

That echo's still here, despite the change in forum server...

[Hoose]

yeah but i dont use big words

[Neil Smith]

Have you got a tap dripping anywhere?

 

Neil

[wren]

Neil: No dripping taps. First thing I checked.

[john6767]

Hot water cooling down? Ours runs for a few sec every so often and I am fairly certain there is no leak, it's just that you turned the top off just before the pump was about to kick in perhaps.

[Giant]

Thanks for all the thoughts.

 

I'm not sure calorifier cooling would explain it, because we're moored up on shore power with an immersion heater regulating the calorifier temperature.

 

The toilet is a hand pumped sea toilet, the flush supply for it comes directly from the tank.

 

Re: accumulator not working correctly, I'm not really clear on how it could fail without water coming out. If there was air leaking out of the air side, surely we'd eventually just have no water pressure without the pump running.

 

I like the idea of putting a non-return valve upstream of the pump. Will give that a try.

[larkshall]

Not just calorifier can cause it. As atmospheric temp changes, the water pressure in the high pressure water side of the plumbing will increase or decrease slightly. An increase will not affect the system, a decrease can be just enough to drop the pressure enough for your pump to cut in for a few seconds. Ive seen this happen even in a power shower system in a house over a few hours.

[Laurie Booth]

Switch the pump on when you want water, that's what I do.

[Guest]

Mine was doing this too and it was driving me mad, especially if it kicked in during the night!

 

Then I found that there was a faulty valve on the washing machine allowing a tiny amount of water through - sorted.

[ditchcrawler]

If you accumulator is working correctly and pressurised to the correct pressure then when the pump does cut in. it should run for several, not 5 seconds to recharge it. How much water can you draw from a tap before the pump cuts in?

[Machpoint005]

If you accumulator is working correctly and pressurised to the correct pressure then when the pump does cut in. it should run for several, not 5 seconds to recharge it. How much water can you draw from a tap before the pump cuts in?

 

I understand the point, but water pump operation is digital - either the pressure is too low and the pump cuts in, or it isn't and it doesn't.

 

If there is a very gradual reduction in system pressure from a tiny weep (eg into the bog) or a reduction in volume in the calorifer as the water cools, the pump cuts in, but it only takes seconds to recharge the accumulator.

 

When you run water through the tap, the pressure doesn't build up again until you turn the tap off -- then the pump keeps on running until the pressure is high enough again. It doesn't take very long even to do that on our boat, though.

[wren]

The pump will kick in few minutes after the tap is opened (it depends on which tap & how much of course) and continues running for "a while" after the tap is closed. I will try to get more specific numbers, but that's all normal operation as I understand it.

 

The original question is about the way the pump spontaneously runs without a tap being opened, though.

[KenK]

We had a similar problem, the PRV on the calorifier had failed, it was passing water not gummed up with lime scale, I replaced it problem solved.

 

Ken

[Giant]

OK I've just done an experiment.

 

Opened a tap until the pump came on, then closed it. Waited for the pump to finish. So the system should be at 25psi.

 

Then opened the tap and filled a container until the pump came on. It took a bit more than a litre, maybe 1.25l or so.

 

Edit to add: if I close the tap as soon as the pump comes on, it runs for about 11 seconds.

Edited June 26, 2015 by Giant

[springy]

OK I've just done an experiment.

 

Opened a tap until the pump came on, then closed it. Waited for the pump to finish. So the system should be at 25psi.

 

Then opened the tap and filled a container until the pump came on. It took a bit more than a litre, maybe 1.25l or so.

 

Edit to add: if I close the tap as soon as the pump comes on, it runs for about 11 seconds.

 

My interpretation (FWIW) - this suggests that there must be a NRV inbetween the pump and accumulator,

and that the NRV and onwards is ok & leak free, therefore the pressure loss causing the pump to activate is local

to the pump i.e. before the NRV, thus the most likely culprit, in the absence of obvious leaks around the pump, is

flow backwards through the pump inlet valve. When the pump does kick in it only takes 5 seconds to repressurise

the feed up to the NRV, rather than the 11 seconds it takes to recharge the accumulator.

 

springy

[ditchcrawler]

The pump will kick in few minutes after the tap is opened (it depends on which tap & how much of course) and continues running for "a while" after the tap is closed. I will try to get more specific numbers, but that's all normal operation as I understand it.

 

The original question is about the way the pump spontaneously runs without a tap being opened, though.

The point I was trying to make was that if the accumulator is working correctly then by the time the water pressure had fallen sufficiently for the pump to start running it should have enough ullage for the pump to run for several second to recharge it.

OK I've just done an experiment.

 

Opened a tap until the pump came on, then closed it. Waited for the pump to finish. So the system should be at 25psi.

 

Then opened the tap and filled a container until the pump came on. It took a bit more than a litre, maybe 1.25l or so.

 

Edit to add: if I close the tap as soon as the pump comes on, it runs for about 11 seconds.

That proves to my mind that the accumulator is working fine. As did your earler reply, so can be discounted. I still wonder if there is a NRV between the pump and accumulator.

Edited June 26, 2015 by ditchcrawler

[Mike on the Wey]

We had this problem, and I too was worried about a leak. The pump had been running for about 10 seconds every 10-15 minutes. I read a tech Q & A in Canal Boat magazine, which gave me the answer.

 

The non-return valve within the pump was allowing water back towards the tank and thus pressure in the system to reduce. A new pump solved the problem, with the added benefit of being much quieter than the old. (Whale UF1215, replaced like for like).

 

I still switch it off at night, but if we don't draw any water for (say) 8 hours and then switch it back on, it doesn't run as the system has maintained the pressure.

 

Edit to correct minor typo.

Edited June 26, 2015 by Mike on the Wey

[Giant]

There is definitely no NRV between the pump and the accumulator tank. I'm looking at them, they're right next to each other with about a foot of pipe between.

[Giant]

Also: I'm not certain about the 5 second number. That was just an order-of-magnitude number really. It might be that when it comes on without a tap being open it runs for 11 seconds. If I hear it go off tonight I'll count the seconds.