hot water heat exchanger

[Richard D]

Drained the hot water heat exchanger over winter by taking off the water pipes, connected the pipes again and later in the day went to draw water from the tap, no water, found water leaking in the bilge. The heat exchanger looks like an emersion heater laying on its side with on one end the two engine water pipes plus cold water supply at the bottom and the hot water outlet at the top and that was all I thought there was, until I traced the leak to a pipe about 5 foot long lying in the builge. I have never noticed the pipe before, from the look of it it does not seem to have any sign of being connected to anything as the end is ragged and not sign of any clips being on it. This pipe is connected to the other end of the unit and presume it is some sort of excess pressure relief pipe.
Any ideas what it does and why it should now be leaking.

Richard


that has never been connected in my time on the boat, lying aboleakin

 

[skip50]

Certainly sounds like the PRV (pressure relief valve). I have the same problem, removed the calorifier tank last autumn, when boat ashore, cleaned up faces of valve which had some calcification on them and reinstalled. Guess what-leaks worse them ever, although only when on mains electric with the element working. New valves can be obtained, but mine didn't seem an exact match, hence my 'refurbishment' of the old valve.

 

[NormanS]

Yes, it sounds like the tube from the pressure relief valve. (When the water in the tank is heated it expands). You are recommended to operate the valve manually, once a month or so, usually by turning it anticlockwise. That makes sure that it is seating alright. Play with the valve, and if necessary, strip it and clean the faces.

 

[Richard D]

The position the unit is fixed makes it impossible to get to the far end to do anything to this valve and to remove the whole unit would be a mamoth job, so I am thinking why not fit another valve to the 1/2 inch diameter hose that comes from the fitted valve. Can you get these new valve assemblies or is there another proprietory unit that could be got from a plumbers merchant. Any idea what pressure they blow off at.

Richard

 

[Sandyman]

The position the unit is fixed makes it impossible to get to the far end to do anything to this valve and to remove the whole unit would be a mamoth job, so I am thinking why not fit another valve to the 1/2 inch diameter hose that comes from the fitted valve. Can you get these new valve assemblies or is there another proprietory unit that could be got from a plumbers merchant. Any idea what pressure they blow off at.

Richard

Can you not even get to the valve to operate it ? If you can, try opening & closing it a few times as it may just be dirt / crud on the valve seat.

Normally they operate at 3 bar, 42 PSI. Trying to think of a reason why not to do as you are contemplating but nothing except mounting the
new valve comes to mind and making good connections !!!!!!!!!!!!!!! hum

 

[Richard D]

Unfortunately I cannot get at the far end of the unit, this is the reason I did not know there was a pipe coming out of that end until I found the water leaking into the bilge. The unit has been fitted in to a small compartment, behind the engine, very neat as far as space saving but useless if any maintenance needed. My unit is purely engine water heated , no mains imersion heater, I find it hard to beleive a pressure relief valve is necessary, as my engine water only gets to 75 C after a lot of engine use so the water cannot be heated above this and I imagine that with heat loss from the pipes to the callorifier the max tempo will be 65 which when warming the water is unlikely to heat it to as much as the input temp, so what chance is there of too much pressue, not a lot. From a pysics point of view what pressure could 65c water produce, not much I would think.

Richard

Richard

 

[Bobobolinsky]

I think, I would rake it out, even though a mammoth task. No point of a bodge and you could empty a lot of water into the bilges at the most inopportune moment.

Take the opportunity to make it more user friendly to service

 

[NormanS]

Something that you could do, if you really cannot access the leaking pressure relief valve, would be to connect an accumulator to the existing tube. In its simplest form, an accumulator is a bit like an inverted plastic lemonade bottle, about 2 litre capacity, but tougher, and more expensive. All that happens is that when the water in the system is heated, and expands, it expands into the accumulator, and compresses the air, in the accumulator, preventing burst pipes and tanks due to excessive pressure.

 

[Richard D]

Understand the princepal but dont think that will work, as with my valve leaking all the time it will fill the "bottle" with water and so no room for expansion again.

Richard

 

[NormanS]

I don't think that you do understand the principle. So where do you think the air will go?

 

[Hoolie]

Two points:

When water is heated it expands and without some outlet can develop enormous pressure, even for a 45 degree rise. It will therefore always come out of your pressure release valve when the engine is running.

If you fit an accumulator or expansion tank as Norman_S suggests the air is contained behind a membrane and compresses when the water pressure rises. Unless you have (yet another) leak the air is retained indefinitely. Pretty well all domestic boilers have a similar expansion tank arrangement.

But evidently your PRV is leaking and needs cleaning up as others have said ... ... ...