Help with a leaking pressurised domestic water system

[Ian_Edwards]

When bought my current boat, I was aware that the pressurised domestic water system leaked.

So far the only leak I've detected is from pressure relief valve on the calorifier, whenever I look at it, it seems to be dripping.

Before I buy and fit a new pressure relief valve. Can anyone advise on how the system should be set up?

The pump is a Par Max 4 and the pressure switch cuts in at 1.4bar (20psi) and cuts out at 2.8bar (40psi).

There is an accumulator in the system, and it's marked with a maximum pressure rating of 4.14 Bar (60 psi), but I've no idea about what the status of the pressure vessel is.

The pressure relief valve looks like a Hot Pot valve set at 3bar, so when the system is cold it shouldn't leak.

However, when the calorifier is heated, by either the engine, emersion heater or Eber Hydronic, the pressure will rise. The expansion should contained by the expansion tank, but the pressure will rise and the difference between the maximum pump pressure of 2.8bar and the relief valve pressure 3.0bar is quite small, so I guess this is why it leaks.

I could replace the pressure relief valve with a 4bar version, or play around with the expansion tank pressure.

Anyone out there with any experience of setting up pressurised domestic hot water systems, who can advise?

 

[Mrnotming]

This problem is widespread and some folks have changed the calorifier relief valve to no effect.Suggest reducing the pressure in the accumulator firstly.However,overnight it may still achieve a pressure in excess of the relief valve.So many folk on here switch off the pump overnight and just accept that the system is poorly designed.
others will disagree,and perhaps by now an OP has a definitive solution.I have not as yet!

 

[theoldsalt]

Ian,

Your pump cuts out at 40psi and your prv is set to relieve at 42psi. These figures are very close together. Almost certainly there will be pressure pulses in the system when the pump and taps operate which could cause the prv to open and dribble. I suggest you either fit a prv with a higher relief pressure or change your pump for a 25psi model. Your suggestion of a change of prv to 4bar (56psi) seems the cheaper solution.

 

[Ian_Edwards]

Thanks for the replies.

I'll order an new 4bar relief valve and try reducing the pressure in the accumulator.

Any idea what the pressure should be???

I've got a reasonable accurate old pressure gauge, which I'll take to the boat next time I go.

I guess that with pump off and a a tap open I should see the residual pressure in the accumulator, but I've no idea what that should be.

 

[HunterWanderer]

Where is the accumulator connected?

There is often a non return valve in the calorifier so the accumulator has to be connected to the output side of the calorifier.

 

[VicS]

Thanks for the replies.

I'll order an new 4bar relief valve and try reducing the pressure in the accumulator.

Any idea what the pressure should be???

I've got a reasonable accurate old pressure gauge, which I'll take to the boat next time I go.

I guess that with pump off and a a tap open I should see the residual pressure in the accumulator, but I've no idea what that should be.

According to this http://www.jabscoshop.com/files/Accumulator and Expansion Tank Instructions ZPWL4 doc595.pdf The accumulator pressure should be 2 - 3 psi below the cut in pressure of the pump


And the pressure in the expansion tank should be set at the pump cut out pressure

.

 

[Ian_Edwards]

Thanks VicS, I wasn't aware there was a difference between an accumulator and an expansion tank.

The link you provided is very useful!

I don't know if the system on Eynhallow is an expansion tank or an accumulator, I'll need to check next time I go to the boat and see if there is a nonreturn valve in the system, and then check the pressure in the tank. I'll then work from there. I've ordered a 4bar pressure relief valve, the old valve has been leaking for so long, my guess is that the sealing faces will be worn, so a new id probaly required.

Once again thank for your help.

 

[jwilson]

I had similar persistent leakage problems from the original and then a new PRV till I fitted a second larger expansion tank between calorifier and taps.

The original setup was a single accumulator tank just after cold supply to taps, which worked OK to keep tap flow reasonably steady. But the PRV leaked often when water heated. Even after changing the PRV (twice) and religiously clicking the valve round to clean the seating every month it still leaked. A second (large as I could conveniently fit) expansion tank sorted the problem.

 

[Ian_Edwards]

Thanks jwilson, that'll be plan "B" then. I'll try a new relief valve and setting the accumulator/expansion tank pressure first.

 

[Mrnotming]

Thanks VicS for the useful Cleghorn Waring link.
With this info I should be able to sort out my system.
Invaluable, thanks again.

 

[duncan99210]

The PRV on my calorifier is connected to a short length of pipe that leads into the fresh water tank, so any water is simply sent back into the tank.....

 

[VicS]

If you ever discover that your domestic cold water supply is getting warm you will know where to look........ if the legionella does not get you first!

 

[johnalison]

My leaking valve is in line and is an odd one with a non-return valve included. Unfortunately the replacement is sitting at home, while I am in Germany. Oddly enough, it has settled down in the last weeks and the pump only cuts in about hourly. You can do without an accumulator if you use one of the newer automatically adjusting pumps, which some boats are now fitted with.

 

[Ian_Edwards]

Re: Help with a leaking pressurised domestic water system - update

Just a note to thank everyone for contributing.

The problem is now solved, I fitted a 4 Bar PRV and pumped up the expansion tank to match the pump, which turned out to be a Sensor Max 17, rated at 17 L/min with a fixed pressure of 2.1 Bar (30psi). The pressure in the expansion tank was low (less than 20psi), so the expansion tank was part filled with water at the working pressure of 2.1 Bar.

Whilst working on the system I also fitted a new 1kW immersion heater element, the old one had some kind of earth or neutral fault, which turned out to be the 240 volt AC power being connected the wrong way around, i.e. the live and neutral were reversed.

Fitting a new immersion heater element, was a real pain, and took a long time because the access was so restricted, but it did mean that I had to drain the calorifier, which in turn means that there is now an air pocket in the top of the calorifier. The air pocket should help by providing additional expansion capacity.

I also have a 4L plastic milk bottle loosely connected by a short hose to the PRV, so I can monitor any leakage. After living on board for a month, the milk bottle is still empty, so I guess the problem is solved for now.