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Pressure release valve leaking...still


Eloisec93
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Hey 

I have a pressure release valve on my calorifyer with a pipe that goes to the engine bilge.

It only leaks a drip every few seconds when the engine is running and heating up hot water in the calorifyer.

 

I have replaced the pressure release valve but the same thing happens. Drip by drip it fills up my engine bilge as the engine is on. When the engine is off no dripping 

 

I don't really understand has anyone got any advice or suggestions?

 

I have an expansion tank near the water tank and water pump. 

 

I know I have posted already but I wanted to post again with the information that I do have an expansion tank.

 

IMG_20211121_091018.jpg

IMG_20211128_195507.jpg

IMG_20211128_185016.jpg

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Do you understand the difference between an accumulator and an expansion vessel?

 

Well of course physically they are the same. The difference is where in the system they are located, and what the air pressure is set to.


If the orange/red thing we can see in the picture is connected just after the water pump, it is an accumulator. It’s purpose is to slow down the rate at which the pump cuts in and out when a tap is partially open.

 

If it is connected to the hot water pipes between the calorifier and the hot water taps, it’s an expansion vessel. It purpose is to limit pressure rise as a cold calorifier heats up (and the water expands).
 

Yes I know the label says “expansion vessel” but it could have been repurposed as an accumulator. Please check whether it’s fitted to the cold water feed after the pump and before the calorifier, or between the calorifier and the hot taps.

 

Even just consider the general location. If it’s next to the pump and cold water tank at the front of the boat, meanwhile the calorifier is near the back of the boat, chances are it’s being used as an accumulator and you don’t have an expansion vessel.

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If it turns out that it definitely is plumbed in as an expansion vessel (which seems unlikely) then maybe the air pressure has leaked away. The black plastic cover visible in the photo unscrews to reveal an air valve, same type as found on car wheels. With the water pump turned off and hot and cold taps open to depressurise the system, the air pressure should be 2.75 bar. You are best using some sort of inflating device like a foot pump with a pressure gauge, because just connecting something to measure the pressure will likely cause some air pressure to be lost.

 

But if the thing is actually being used as an accumulator, the correct inflation pressure is about 1 bar, hence why I said it’s important to identify whether it’s being used as an expansion vessel or an accumulator.

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From what I understand your PRV appears to be doing what it should, releasing water pressure from your calorifier as the engine runs, heating the water causing its volume to expand. The problem is your vent pipe has been run into your bilge which I think is quite a common set up. I presume you rely on a bilge pump to pump it out? Mine is vented directly overboard via a skin fitting so the bilge stays dry. 

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8 minutes ago, MichaelG said:

From what I understand your PRV appears to be doing what it should, releasing water pressure from your calorifier as the engine runs, heating the water causing its volume to expand. The problem is your vent pipe has been run into your bilge which I think is quite a common set up. I presume you rely on a bilge pump to pump it out? Mine is vented directly overboard via a skin fitting so the bilge stays dry. 

 

But with an expansion vessel in the hot pipes the PRV should not leak and the one shown looks adequate.

 

Right at the start of this in another post  the OP was told that a leaking PRV could be a faulty PRV, no expansion vessel, or the pump cut out pressure too high. To the best of my knowledge she has changed the PRV so as long as the old and new one are of the same release pressure that can be ruled out.

 

I do not recall seeing the pump cut out pressure so that could still be the problem as could low pressure in the red expansion vessel (if that is  wgat it is and not an accumulator) so the steps needs are:

 

1. Establish if the red thing is an accumulator or expansion vessel.

2. If is is an expansion vessel pressurise it to the cut out pressure marked on the water pump as described by Nick except my view is that the small amount of pressure lost when using an ordinary tyre gauge can be ignored.

3. Run the system up to pressure and remeasure the pressure in the expansion vessel. This will be the pump cut out pressure so should be no higher than the markings on the pump. If it is higher then I would try adjusting the pump, fit a remote pressure switch, or if needs must fit a new pump.

 

 

 

 

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4 minutes ago, Tony Brooks said:

 

But with an expansion vessel in the hot pipes the PRV should not leak and the one shown looks adequate.

 

Right at the start of this in another post  the OP was told that a leaking PRV could be a faulty PRV, no expansion vessel, or the pump cut out pressure too high. To the best of my knowledge she has changed the PRV so as long as the old and new one are of the same release pressure that can be ruled out.

 

I do not recall seeing the pump cut out pressure so that could still be the problem as could low pressure in the red expansion vessel (if that is  wgat it is and not an accumulator) so the steps needs are:

 

1. Establish if the red thing is an accumulator or expansion vessel.

2. If is is an expansion vessel pressurise it to the cut out pressure marked on the water pump as described by Nick except my view is that the small amount of pressure lost when using an ordinary tyre gauge can be ignored.

3. Run the system up to pressure and remeasure the pressure in the expansion vessel. This will be the pump cut out pressure so should be no higher than the markings on the pump. If it is higher then I would try adjusting the pump, fit a remote pressure switch, or if needs must fit a new pump.

 

I was wondering what the grey box thing is to the left of the pump in the last photo. Since it seems to have wires that go to the pump, is it an external pump pressure switch?

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Just now, nicknorman said:

I was wondering what the grey box thing is to the left of the pump in the last photo. Since it seems to have wires that go to the pump, is it an external pump pressure switch?

 

Well done, yes it is, I was so busy looking at the expansion vessel thing I did not notice it. So if the OP has been twiddling the screw in the end of the pump it is probably the wrong cut out pressure adjustment, She needs the  nut under the grey plastic cover.

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Just now, nicknorman said:

I was wondering what the grey box thing is to the left of the pump in the last photo. Since it seems to have wires that go to the pump, is it an external pump pressure switch?

That is indeed a square D pressure switch! Didn’t even look at the pic! Whoops! Well that’s better than the internal one found on pumps. If the OP makes a note of the model number they can find it’s rated on/off pressure online together with instructions on how to adjust the cut in/out pressure. There are many different models but they all use the same principle. An easy way to read cut in/out pressure is to depressurise the accumulator & fit a digital tyre pressure gauge to the valve…once the switch is set on then pump the accumulatior back up.  

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1 hour ago, MichaelG said:

From what I understand your PRV appears to be doing what it should, releasing water pressure from your calorifier as the engine runs, heating the water causing its volume to expand. The problem is your vent pipe has been run into your bilge which I think is quite a common set up. I presume you rely on a bilge pump to pump it out? Mine is vented directly overboard via a skin fitting so the bilge stays dry. 

 

Sadly this is plain wrong. The PRV should not be dripping. 

 

The PRV (pressure relief valve) is a safety device which under correct conditions will not be operating. It should NOT be dribbling water, ever. 

 

The PRV dripping water indicates the presence of a system fault which needs fixing. It might be a design fault, or a component failure. Others here have already explained the possibilities in detail.

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9 minutes ago, MtB said:

 

Sadly this is plain wrong. The PRV should not be dripping. 

 

The PRV (pressure relief valve) is a safety device which under correct conditions will not be operating. It should NOT be dribbling water, ever. 

 

The PRV dripping water indicates the presence of a system fault which needs fixing. It might be a design fault, or a component failure. Others here have already explained the possibilities in detail.

I agree, although the “design fault” is fairly common I suspect. Our boat didn’t have an expansion vessel (but did have a NRV at calorifier input). The boatbuilder felt it was a good thing that the PRV was exercised regularly. At the time I didn’t know any better but now I do!

 

So for the last 10 years we’ve not had an expansion vessel. For the last 5 years or so it’s been on my round tuit list. I finally fitted one a month or two ago. This was prompted by the immersion heater starting to trip the mains RCD. Horizontal calorifier with immersion heater halfway along at the top (more normally at the end, I think)?

Took plastic cover off immersion - lots of water and wet foam. Stable door bolted etc.

 

Fortunately it turned out to be a leak through the rubber O ring that sealed the immersion thread. Replaced with a flat fibre gasket it still leaked. Worrying! But when I added some sinful PTFE tape it stopped leaking, I think mostly because the tape lubricated the threads and allowed me to get it a bit tighter (access only possible with 1 hand).

 

Phew, so the calorifier hadn’t split (yet) which was lucky.

 

Anyway the moral is that routinely exercising the calorifier up to its maximum pressure is BOUND to shorten its life!

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2 hours ago, nicknorman said:

I agree, although the “design fault” is fairly common I suspect. Our boat didn’t have an expansion vessel (but did have a NRV at calorifier input). The boatbuilder felt it was a good thing that the PRV was exercised regularly. At the time I didn’t know any better but now I do!

 

So for the last 10 years we’ve not had an expansion vessel. For the last 5 years or so it’s been on my round tuit list. I finally fitted one a month or two ago. This was prompted by the immersion heater starting to trip the mains RCD. Horizontal calorifier with immersion heater halfway along at the top (more normally at the end, I think)?

Took plastic cover off immersion - lots of water and wet foam. Stable door bolted etc.

 

Fortunately it turned out to be a leak through the rubber O ring that sealed the immersion thread. Replaced with a flat fibre gasket it still leaked. Worrying! But when I added some sinful PTFE tape it stopped leaking, I think mostly because the tape lubricated the threads and allowed me to get it a bit tighter (access only possible with 1 hand).

 

Phew, so the calorifier hadn’t split (yet) which was lucky.

 

Anyway the moral is that routinely exercising the calorifier up to its maximum pressure is BOUND to shorten its life!

Mmm interesting. I don't think my system has an expansion vessel fitted, just an accumulator, I think I would have seen it unless it's really tucked away. I shall have to have a good root around and follow the hot pipes to check. I wouldn't know if the PRV activates regularly as it is vented overboard rather than into the bilge. 

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1 minute ago, MichaelG said:

Mmm interesting. I don't think my system has an expansion vessel fitted, just an accumulator, I think I would have seen it unless it's really tucked away. I shall have to have a good root around and follow the hot pipes to check. I wouldn't know if the PRV activates regularly as it is vented overboard rather than into the bilge. 

 Our calorifier didn't come with any fittings such as mixer valves etc (it's not a surecal one) and so the NRV was external, just a very short length of pipe away from the cold water inlet. However this allowed me to add the expansion vessel on the cold side of the calorifer (between the NRV and the calorifier) which is the best place for it, since if it is on the hot side, it fills with hot water which then cools because it is not insulated. So you have to leave the hot tap open whilst the now cold water in the expansion vessel comes out, before hot starts arriving from the calorifier. So my point is that an EV might be on the cold side, between the NRV and the calorifier.

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30 minutes ago, nicknorman said:

 Our calorifier didn't come with any fittings such as mixer valves etc (it's not a surecal one) and so the NRV was external, just a very short length of pipe away from the cold water inlet. However this allowed me to add the expansion vessel on the cold side of the calorifer (between the NRV and the calorifier) which is the best place for it, since if it is on the hot side, it fills with hot water which then cools because it is not insulated. So you have to leave the hot tap open whilst the now cold water in the expansion vessel comes out, before hot starts arriving from the calorifier. So my point is that an EV might be on the cold side, between the NRV and the calorifier.

Thanks for the advice. My calorifier, pump, accumulator and associated gubbins is all housed under the bed which has to be taken apart to get a clear view of everything. I'll have to have a good look to see if there's an expansion vessel hiding in there. Interestingly I don't get the burst of cold water before hot from the hot tap you mention but conversly when I have a tank of hot water my cold tap runs warm for a few seconds before coming through cold.  

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My NRV was just after the pump with the PRV just on the tap side and vented back to the inlet side of the pump with just an accumulator on just downstream of the PRV. This is very unconventional but it allowed all the parts of the water system to be mounted a board that could be removed for the winter and taken home. The accumulator also acted as an expansion vessel. It sounds as if yours might be similar. The downside is that there will be an interface of how and cold water where bacteria might breed and if the last co;d tap is close to the calorifier hot/warm water might come out of it for a few seconds. Mine had about a 20ft pipe run so there was no problem.

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19 minutes ago, MichaelG said:

Thanks for the advice. My calorifier, pump, accumulator and associated gubbins is all housed under the bed which has to be taken apart to get a clear view of everything. I'll have to have a good look to see if there's an expansion vessel hiding in there. Interestingly I don't get the burst of cold water before hot from the hot tap you mention but conversly when I have a tank of hot water my cold tap runs warm for a few seconds before coming through cold.  

That rather sounds like you don't have an NRV. As the calorifier heats up and the water expands, it pushes back into the cold system, the increased pressure mostly being absorbed by the accumulator. If you don't have an NRV then there is no point in having an expansion vessel.

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8 minutes ago, Tony Brooks said:

My NRV was just after the pump with the PRV just on the tap side and vented back to the inlet side of the pump with just an accumulator on just downstream of the PRV. This is very unconventional but it allowed all the parts of the water system to be mounted a board that could be removed for the winter and taken home. The accumulator also acted as an expansion vessel. It sounds as if yours might be similar. The downside is that there will be an interface of how and cold water where bacteria might breed and if the last co;d tap is close to the calorifier hot/warm water might come out of it for a few seconds. Mine had about a 20ft pipe run so there was no problem.

Thanks for the advice Tony. You could well be right as the calorifier is only about six feet from the bathroom sink and shower and about ten feet from the galley sink.

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6 hours ago, nicknorman said:

Anyway the moral is that routinely exercising the calorifier up to its maximum pressure is BOUND to shorten its life!

 

Yes, just like it did on De Havilland Comets. Weird that the concept of metal fatigue was little understood until they started falling out of the sky and extensive investigations discovered the effect. Where repeated straining of metal well within its elastic limit still leads to fracturing. I think we see the same thing happening to calorifiers in boats when they have no expansion vessel.

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1 hour ago, ditchcrawler said:

I think mine is dribbling, ether that or its going back through the pump. Mine is plumbed into the basin waste so I decided to block the outlet to see if the level came up in the basin. The pump didn't cut in once.

 


im not sure that plumbing it into the basin waste is the best idea. In the event of an overheat caused by eg an immersion heater runaway (which I grant you is pretty unlikely) such that the water hits boiling point at pressure, when the PRV opens scalding hot steam / water would come out, and continue to come out since as the pressure drops so does the boiling point. Not nice to get a face-full of scalding steam whilst preening yourself in the basin mirror!

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10 minutes ago, nicknorman said:


im not sure that plumbing it into the basin waste is the best idea. In the event of an overheat caused by eg an immersion heater runaway (which I grant you is pretty unlikely) such that the water hits boiling point at pressure, when the PRV opens scalding hot steam / water would come out, and continue to come out since as the pressure drops so does the boiling point. Not nice to get a face-full of scalding steam whilst preening yourself in the basin mirror!

Saving grace there, no immersion. It seemed like a good idea at the time as they say

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16 hours ago, Eloisec93 said:

 

 

I have an expansion tank near the water tank and water pump. 

 

I know I have posted already but I wanted to post again with the information that I do have an expansion tank.

 

 

IMG_20211128_195507.jpg

IMG_20211128_185016.jpg

 

That looks more like it's an accumulator tank to me as it's near the water pump and (cold) water tank so I'd assume it's connected to your cold pipes.

 

You need to have a look for the same sort of vessel connected to the hot water system near your calorifier. It could be some distance from the calorifier but would likely be in the vicinity.

16 hours ago, nicknorman said:

Do you understand the difference between an accumulator and an expansion vessel?

 

 

I don't think so....

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21 hours ago, nicknorman said:

Yes I know the label says “expansion vessel” but it could have been repurposed as an accumulator. Please check whether it’s fitted to the cold water feed after the pump and before the calorifier, or between the calorifier and the hot taps.

 

Even just consider the general location. If it’s next to the pump and cold water tank at the front of the boat, meanwhile the calorifier is near the back of the boat, chances are it’s being used as an accumulator and you don’t have an expansion vessel.

 

Also, I find myself wondering what's inside that big mass of what looks like insulation inside red polythene to the right of the vessel in the photo. Looks to me like an old style hot water cylinder jacket  Could this boat have two calorifiers perhaps? 

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Another think that looks a bit odd. Mounted on the left of the blue calorifier there is what looks like the PRV but it has  a sliver "something" fitted at its base and there seems to be a small plastic pipe or round cable coming from it. No idea what that is.

 

And lower right of the accumulator/expansion vessel there is a blue "something" with brass at its top end.  I cant see what it is  connected to but it looks unusual to me.

 

Edited to add, further inspection of the set of photos suggest it must be a connection on the pump taken at a funny angle.

Edited by Tony Brooks
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