Fesh Water in the Bilge

tomg

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Last Wednesday on the boat, stayed the night, immersion heater on (stat set to lowest setting-water hand hot), fresh water pump 'cycles' every 15/20mins or so as if a tap is dripping. Check the bilge in the morning, full of fresh water - bilge auto switch not working!. Culprit appears to be hot water cylinder with water escaping from pressure relief valve. This happened on-passage a couple of years ago when water got very, very hot and I lost most of a tank full into the bilge and the auto pump drained it overboard. Changed pressure relief valve to,I think, 1.5 or 2 bar(anyway highest available). What is happening now though? Faulty valve again perhaps but why when water is only modestly hot - P1V1T1 etc. Never ever had this problem on previous boats. Faulty design of water system? Should I have an accumulator tank and would this solve the problem - but how/why? Only suggestion so far is to replace press.relief valve with a solid plug but this doesn't seem sensible to me.Any advice greatfully received.
 
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Anonymous

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"P1V1/T1" applies only to gasses, not liquids (it comes from the General Gas Equation, PV=nRT). Putting an accumulator into the system will act as a relief as the amount that a liquid expands is fairly small - well within the range of a typical accumulator. Buy an accumulator that has a max pressure a fair bit above your pump cut-out pressure. Of course this will only solve the problem if your diagnosis is correct. If your leak is due to something else then the accumulator won't help!

Accumulators are a 'good thing' on a boat. Once you've had one you wouldn't want to be without one.
 

TrueBlue

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Could solution be even simpler - The over pressure valve is a simple spring loaded device and IME sometimes gets a bit of gunge (limescale) in the seal when the device is off pressure.

There is usually a twist cap on the top which, I suppose, is intended to test the unit. Turning this - clicking it, when you switch on the main pump and bring it up to pressure cleans the valve - ore at least reseals it. Worked for me. Give it a try before spending loads of money?
 

Robin

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Also if you like bone dry bilges as we do, plumb the relief valve hose overboard!

Most HW systems leak water from the relief valve, usually because the system gets pressurised from the pressure pump plus the immersion (which has a thermostat limiting the max temp) then when you run the engine it heats up more (to the temperature of the thermostat setting on the engine) and pressurises the system more. However you do seem to be leaking rather a lot of HW so maybe the relief valve is faulty.
 

snowleopard

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<Should I have an accumulator tank and would this solve the problem>

yes, and probably.

as the water heats up it expands and has nowhere to go so chances are it'll lift the safety valve. it's not a compressable gas so you could build really high pressure with a very small increase in volume of water. that would only release a fairly small volume unless the valve sticks open. if you fit an accumulator, make sure it is between any one-way valve and the cylinder
 

tomg

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Thanks for all the advice. I am going to try and clean the valve and fit an accumulator.The P1T1..thing just goes to show what you think you remember from school physics over 45 years ago. I wonder what else I am certain about which is equally wrong. I really will have to start taking more notice of the strange looks I get from people occaisionally. Up until now I thought it must be that I am incredibly knowledgable and fascinating. Thanks again. /forums/images/graemlins/smile.gif
 
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[ QUOTE ]
I wonder what else I am certain about which is equally wrong. I really will have to start taking more notice of the strange looks I get from people occaisionally. Up until now I thought it must be that I am incredibly knowledgable and fascinating.

[/ QUOTE ]You're not alone /forums/images/graemlins/wink.gif
 
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