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Posted: Tue Jan 04, 2011 10:20am

Post Subject: Non return valve calorifier

Tony, On draining down my cold water system for the winter, I found that after switching off the water pump, shutting off the supply from my water tank, and opening the taps to drain water etc. when opening a drain valve fitted in the plastic pipe close to the calorifier cold water inlet, I was able to drain cold water from the calorifier. Although I was initially happy to be able to take a quantity of water out of the calorofier, I thought that they were fitted with an integral non-return valve on there inlet side connection to the cold supply, is this correct? I then decided to drain any residual water from the flexible pipe connecting the cold water supply to the toilet, only to find it kept running (no water pump operating as it was switched off and isolated as previously described. As there is an isolating valve to the toilet supply I turned it off. My only explanation is that if there is not a non return valve fitted to the calorifier this must be caused by the calorifier (water head pressure) causing the water to flow back. Does this sound plausible, and if so what do you recommend? I was thinking of fitting a non return valve if necessary before the calorifier thus allowing me to drain the cold system thouroughly, at present I would have to fully empty the calorifier. Thanks Duncan

Tony-B
Tony-B

Posted: Tue Jan 04, 2011 10:43am

Post Subject: Non return valve calorifier

Dear Duncan, whatever gave you the idea that calorifiers had an internal NRV? The expensive ones designed for sea use that come already plumbed with goodness knows what on them probably do have an NRV but that is in the external pipe work. Ordinary foam covered copper cylinders as used for many inland boats are just very strong versions of domestic indirect cylinders.I suspect the water flowing from the toilet may have been more to do with the head of the water in the tap spurs because it can be very hard to drain a calorifier unless you let air in at the top by either loosening a connections or turning the pressure relief valve so it is held off its seat. Now the wisdom of leaving a calorifier full of water is for you to judge - even a well insulated one. I do not see how you can fully drain the cold water system (or the hot) without a low level drain *replaced* because of the taps are higher than the pipe runs usually. The drain *replaced* by the calorifier may have been designed to do this. However there is still the question of water trapped in the hot pipes etc. To fully protect the system you would have to drain the hot & cold pipework, including the calorifier, toilet, shower mixer and even the water pump. To absolutely minimise the dangers of frost damage it might be a good idea to take the water pump & shower mixer home with you for the winter. I would also want to make sure no water is trapped in the toilet mechanism (whatever type it is) because turning a valve off without ensuring the toilet mechanism is dry makes it more likely that freezing water in the toilet mechanism would burst something rather than push water back into the pipework and out of a tap. By all means fit a NRV at the calorifier inlet but be aware that in doing so you may render any expansion vessel fitted into the cold supply inoperative, but expansion vessels and accumulators are another whole topic. Tony Brooks

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Posted: Tue Jan 04, 2011 2:55pm

Post Subject: Non return valve calorifier

Tony, I understood that it is good practice to fit a NRV, and that some calorifiers had them fitted as standard. In any event the calorifier is a vertical type and the water head is approx 3 foot above the toilet hose connection, are you saying that this water head is insufficient to allow a flow from the hose when disconnected from the toilet inlet? Duncan

Tony-B
Tony-B

Posted: Tue Jan 04, 2011 4:10pm

Post Subject: Non return valve calorifier

I said some calorifires probably have NRVs fitted as standard but not INTERNAL ones. The expensive ones may well have NRVs fitted to the factory fitted EXTERNAL pipework. All I advised was that it can be very difficult to persuade a calorifier to drain down unless you allow air into the top. I made no mention of the head being sufficient or insufficient to allow this. I suspect the problems I and others have found is that the hot tap jumpers are sucked onto their seats, thus preventing air being drawn through the taps. In this way the depression in the hot pipework would prevent water draining from the calorifier. I do not know if this is the case but as far as I can see its the most likely explanation. I just want you to be aware that calorifiers might not drain as easily as you seem to think. Tony Brooks

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Posted: Tue Jan 04, 2011 4:48pm

Post Subject: Non return valve calorifier

Tony, I am only trying to be able to drain the pipework without having to drain the calorifier, if as it seems for whatever reason the calorifier is emptying through this low level drain tap or toilet inlet hose, (and there is a gurgling sound coming from the calorifier when the drain tap is open)then presumably I need to fit a NRV in the external pipework between the calorifier cold water input and the drain tap, does this sound ok? If there is no NRV fitted does any pressure build up due to hot water expansion in the calorofier not cause a problem with back pressure in the cold feed, and if so could this cause any damage to accumulator and/or water pump, I am wondering if the pressure would blow back through the system rather than through the Pressure Release Valve on the calorifier? Duncan

Tony-B
Tony-B

Posted: Tue Jan 04, 2011 5:48pm

Post Subject: Non return valve calorifier

If what you describe as an accumulator really is an accumulator then fitting a non-return valve in the calorifier inlet should cause no problems what so ever. If however it's an expansion vessel (same item, different pressure and different task)then fitting the non-return valve will prevent it working so the pressure relief valve will have to deal with all water expansion. However I would question the wisdom of trapping water in the calorifier in the light of the reports I have seen of frost damaged calorifiers over the last few weeks. Just to be clear. Draining the cold pipework will not drain the hot so that will still be subject to frost damage. You also have a set of NRVs in the water pump and as water may be considered incompressible they will prevent the expanding hot water coming back into the cold system. However the accumulator will allow some hot water to start to flow back but how much and how hot is open to question. The PRV that you should have close to or on the calorifier outlet should prevent any damage to the system. Tony Brooks

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Posted: Tue Jan 04, 2011 6:03pm

Post Subject: Non return valve calorifier

Tony, Thanks, I have checked the boat manual issued by the builder and they refer to the device as an "expansion vessel" it is fitted close to the water pump outlet. Next time I am on the boat I will allow as much water as possible to drain from the system, even if this means emptying the calorifier. However I have noted some concerns you have raised in past responses regarding the lack of support to the internal heating coils after the surrounding water is removed, is this an issue with only certain types/ages of calorifier? Duncan

Tony-B
Tony-B

Posted: Tue Jan 04, 2011 7:37pm

Post Subject: Non return valve calorifier

All I can say about that is that I was warned about the potential for such failures by one of my plumbing lecturer colleagues. I, myself have never experienced a failure of a vertical calorifier when drained but have experience a couple of horizontal ones with internal failure. The failures may have down down to a design flaw but as no one can see inside the calorifier I have to mention the possibility simply to protect the magazine and myself. After the last few weeks I think you will be very wise to drain down the calorifier. I suspect the danger of frost damage is more than the danger of vibration failure with a drained system. Tony Brooks

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