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Calorifier pressure release valve


Dave .Morialta

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So my calorifier is under the bed and the release valve appears to be piped under floor . The water which is not much collects under the floor in the corner. I assume its to low down to connect to a waste outlet however could i fit something like a container that the water feeds into to save me having to mop up the water.

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9 minutes ago, Dave .Morialta said:

could i fit something like a container that the water feeds into to save me having to mop up the water.

Yes of course but the question arises “why is the PRV leaking in the first place?”

 

Do you have an expansion vessel in the hot circuit? Does it still work?  Have you rotated the PRV to ensure that it’s seated correctly?

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1 minute ago, Dave .Morialta said:

Its not leaking but surely it there to release the pressure which will mean a small amount of water coming out.

Not in a properly designed system.

It is ideally there as a precaution, not something that will dribble as part of normal operation.

If you have an adequate hot water expansion vessel, as per WotEver's question, then that should control any expansion, with no need for PRV drip.

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13 minutes ago, Dave .Morialta said:

There is a expansion tank on heating system but not direct of water cylinder 

Yes, you really need  one on the hot water outlet side of the calorifier.

If it were a Surejust/Surecal calorifier, they make this very clear, and will not cover a calorifier under warranty if one is not fitted.

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Hi

Ok i now understand what actually happens from reading another post on here. It would appear that systems can be installed with or without an expansion tank although better to have one. What i think i will do is fit a vessel so i can see how much is actually coming out then decide which way to go. Thanks everyone plumbing and me don't get on ? 

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42 minutes ago, Mike the Boilerman said:

 

Hardly.

 

The PRV is a safety device, which will only discharge under fault conditions. 

 

Ergo, we know the OP's installation has a fault. 

 

 

While I don't doubt either your expertise or the literal accuracy of your diagnosis, is it important if there is a small discharge?

 

My PRV used to leak into the bilge through a pipe provided for the purpose. When I had some (5 figures worth of) work done on the boat last winter, the yard (in passing and without reference to me) cut a new skin fitting for this pipe. They did not charge for this and could, presumably, have changed the PRV or altered the pressure in the expansion tank at less cost to them.

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15 hours ago, alan_fincher said:

Yes, you really need  one on the hot water outlet side of the calorifier.

If it were a Surejust/Surecal calorifier, they make this very clear, and will not cover a calorifier under warranty if one is not fitted.

Only necessary if there is a NRV between the accumulator on the cold side and the calorifier feed (and if that accumulator is adequately sized for expansion).

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3 minutes ago, Onewheeler said:

Only necessary if there is a NRV between the accumulator on the cold side and the calorifier feed (and if that accumulator is adequately sized for expansion).

I was just going to say that but you beat me to it, more succinct than I could have been. 

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4 minutes ago, Onewheeler said:

Only necessary if there is a NRV between the accumulator on the cold side and the calorifier feed (and if that accumulator is adequately sized for expansion).

Indeed. My system has a NRV on the outlet side of the calorifier only, and our accumulator is very small but we get no leakage from the PRV.

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3 minutes ago, Keeping Up said:

Indeed. My system has a NRV on the outlet side of the calorifier only, and our accumulator is very small but we get no leakage from the PRV.

I suspect that in most installations a NRV is solving an imaginary problem. Our NB hasn't got one, and our shared oil tanker used to have one until I took it out. The latter enabled me to remove the expansion tank and repurpose some space in a cupboard.

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9 hours ago, frahkn said:

While I don't doubt either your expertise or the literal accuracy of your diagnosis, is it important if there is a small discharge?

 

 

The calorifier is capable under certain conditions of turning into a small bomb. Very unlikely to happen, but possible. (The condition being when the immersion heater thermostat jams ON and the water in the calorifier rises to 100c and as it begins to boil, the pressure rises and along with it the boiling point so the water temp creeps up too, above 100c. Eventually the tanks splits and 40 litrs of water at say 5 bar and 110c instantaneously turns to steam. You don't want this to happen, you really REALLY REALLY don't.) The main defence against this is the PRV on a boat as there is no combined "temperature & pressure relief valve" as fitted to a house calorifier, so straight away one of the normal safety devices is missing. Now if your one single safety device is dribbling intermittently, it is operating when it should not be, which is a fault in itself. Yes is it 'failing safe', but when it is doing this, it is telling you about another fault i.e. that the pressure in the calorifier is creeping up too high. If you don't care about this then fine, no particular consequences other than a split calorifier eventually, but if you like things to be 'just so' and right, then this needs fixing and yes it is important.

 

 

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14 minutes ago, Mike the Boilerman said:

 

The calorifier is capable under certain conditions of turning into a small bomb. Very unlikely to happen, but possible. (The condition being when the immersion heater thermostat jams ON and the water in the calorifier rises to 100c and as it begins to boil, the pressure rises and along with it the boiling point so the water temp creeps up too, above 100c. Eventually the tanks splits and 40 litrs of water at say 5 bar and 110c instantaneously turns to steam. You don't want this to happen, you really REALLY REALLY don't.) The main defence against this is the PRV on a boat as there is no combined "temperature & pressure relief valve" as fitted to a house calorifier, so straight away one of the normal safety devices is missing. Now if your one single safety device is dribbling intermittently, it is operating when it should not be, which is a fault in itself. Yes is it 'failing safe', but when it is doing this, it is telling you about another fault i.e. that the pressure in the calorifier is creeping up too high. If you don't care about this then fine, no particular consequences other than a split calorifier eventually, but if you like things to be 'just so' and right, then this needs fixing and yes it is important.

 

 

Thanks Mike.

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44 minutes ago, Onewheeler said:

Only necessary if there is a NRV between the accumulator on the cold side and the calorifier feed (and if that accumulator is adequately sized for expansion).

Yes, but I made reference to Surejust/Surecal, and these do have a pre-plumbed NRV, hence why they need the EV, and they are not warrantied by Surejust without one.

A lot of boats, (most, possibly?), do not have a old water accumulator that is adequately sized to act reliably as an EV for heating water in a large calorifier.

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11 hours ago, frahkn said:

While I don't doubt either your expertise or the literal accuracy of your diagnosis, is it important if there is a small discharge?

 

My PRV used to leak into the bilge through a pipe provided for the purpose. When I had some (5 figures worth of) work done on the boat last winter, the yard (in passing and without reference to me) cut a new skin fitting for this pipe. They did not charge for this and could, presumably, have changed the PRV or altered the pressure in the expansion tank at less cost to them.

A small discharge indicates that the pressure in you calorifier has exceeded the pressure rating of the pressure relief valve. With hydrostatic pressure, ie solid liquid, no air you only need a small volume of water to give a large pressure increase. Some people fit pressure relief valves that are very close the the maximum pressure rating of the calorifier

 

Edited by ditchcrawler
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3 hours ago, ditchcrawler said:

A small discharge indicates that the pressure in you calorifier has exceeded the pressure rating of the pressure relief valve. With hydrostatic pressure, ie solid liquid, no air you only need a small volume of water to give a large pressure increase. Some people fit pressure relief valves that are very close the the maximum pressure rating of the calorifier

 

I admit that I do not know the setting of the PRV or the pressure rating of my calorifier. I have not touched either since I bought the boat.

 

On the other hand, the PRV has been seeping since I bought the boat as well (and does so whether on shore power with the immersion heater or with only engine heating). It's been seven years now so I expect my inertia will continue until I hear the bang!

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A dribbling PRV sounds typical of hydraulic pressure due to not having an expansion vessel, I've spoken to a few people who thought weeping was normal behaviour, one of them did his own fitout and didn't fit an exp vessel or accumulator thinking his variable pressure pump negated the need for one, he had no idea what I was on about when I tried to explain how hydraulic pressure made his PRV weep.

 

Having a PRV pressure release close to the pump pressure can be a bit annoying at times but it does confirm it's working. 

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1 hour ago, nb Innisfree said:

Having a PRV pressure release close to the pump pressure can be a bit annoying at times but it does confirm it's working. 


Also confirms the system is badly designed and/or incorrectly specified. 
 

 

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22 hours ago, Mike the Boilerman said:

 

The calorifier is capable under certain conditions of turning into a small bomb. Very unlikely to happen, but possible. (The condition being when the immersion heater thermostat jams ON and the water in the calorifier rises to 100c and as it begins to boil, the pressure rises and along with it the boiling point so the water temp creeps up too, above 100c. Eventually the tanks splits and 40 litrs of water at say 5 bar and 110c instantaneously turns to steam. You don't want this to happen, you really REALLY REALLY don't.) The main defence against this is the PRV on a boat as there is no combined "temperature & pressure relief valve" as fitted to a house calorifier, so straight away one of the normal safety devices is missing. Now if your one single safety device is dribbling intermittently, it is operating when it should not be, which is a fault in itself. Yes is it 'failing safe', but when it is doing this, it is telling you about another fault i.e. that the pressure in the calorifier is creeping up too high. If you don't care about this then fine, no particular consequences other than a split calorifier eventually, but if you like things to be 'just so' and right, then this needs fixing and yes it is important.

 

 

Small point of order but my Cleghorn Waring supplied calorifier has a combined temp & pressure valve. I don’t know if they still supply them with the unit. They are made by Honeywell I think. Quite a nice design as you can strip them without removing the fitting if they need cleaning. 

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16 minutes ago, frangar said:

Small point of order but my Cleghorn Waring supplied calorifier has a combined temp & pressure valve.

 

Is this in addition to the PRV or instead of? 

 

Domestic calorifiers have both. A PRV calibrated to 2 or 3 Bar and a T&P valve calibrated to open at usually 5 or 6 Bar or 90c. 

 

 

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5 minutes ago, Mike the Boilerman said:

 

Is this in addition to the PRV or instead of? 

 

Domestic calorifiers have both. A PRV calibrated to 2 or 3 Bar and a T&P valve calibrated to open at usually 5 or 6 Bar or 90c. 

 

 

It’s one of these

 

https://www.jabscoshop.com/pressure-systems/c-warm-heaters/c-warm-heater-accessories/cw415-c-warm-temperature-and-pressure-relief-valve-3bar.htm

 

It’s supposed to be a PRV as well....as I’ve got a expansion vessel I’ll only know when it blows up. Btw the immersion I’ve fitted has a high temp cut out as well as the normal stat. 
 

edited to add

 

I might have been mistaken about not removing it to clean...it is possible to strip it down tho as mine did get a dribble when I hadn’t pumped up the expansion vessel for a while. 

Edited by frangar
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16 minutes ago, frangar said:

 

Yes that offers far better protection than a simple PRV as it will open (hopefully) if the temp approaches boiling point, and bring in fresh cold water to the calorifier in the event of the heater thermostat contacts welding themselves together,. as they regularly do.

 

 

19 minutes ago, frangar said:

It’s supposed to be a PRV as well...

 

Yes it is. The problem is that PRVs tend to stick closed if left untested for long periods of time, hence the fitting of a separate PRV on household calorifiers. Twice the chance of one or the other opening in fault conditions. 

 

 

20 minutes ago, frangar said:

Btw the immersion I’ve fitted has a high temp cut out as well as the normal stat. 

 

Yes this is a legal requirement nowadays for immersion heaters in houses, since the death of two children about 20 years ago. Not for boats, but any immersion heater thermostat manu not incorporating overheat disconnection for a boat heater would have a hard time in court illustrating they had designed responsibly in the event of an explosion, if they had not incorporated one. So I'd expect all immersion heater/stats to have overheat protection built in nowadays.

 

 

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