Accumulator tank for hot water

[blackrose]

I have an accumulator tank fitted downstream of my water pump, but I've just bought another one to install into my hot water system because I was warned that with the one-way valve fitted in the cold water feed to the calorifier I had created a pressure vessel and needed to let the hot water expand. I'm not sure where the expansion is going at the moment - perhaps it's just being taken up by the plastic pipes and expansion of the calorifier itself.

 

Anyway, a friend bought me an ordinary red 8 litre accumulator tank from a plumbing shop quite cheaply which I'm going to T into the cold water feed pipe downstream of the one way valve. The only thing is it doesn't say whether it's for use with hot or cold water so does anyone know if it's ok, or do you need special accumulator for hot water systems?

Edited January 4, 2007 by blackrose

[Ernie]

I have an accumulator tank fitted downstream of my water pump, but I've just bought another one to install into my hot water system because I was warned that with the one-way valve fitted in the cold water feed to the calorifier I had created a pressure vessel and needed to let the hot water expand. I'm not sure where the expansion is going at the moment - perhaps it's just being taken up by the plastic pipes and expansion of the calorifier itself.

 

Anyway, a friend bought me an ordinary red 8 litre accumulator tank from a plumbing shop quite cheaply which I'm going to T into the cold water feed pipe downstream of the one way valve. The only thing is it doesn't say whether it's for use with hot or cold water so does anyone know if it's ok, or do you need special accumulator for hot water systems?

There is usually a pressure relief valve at the top of the calorifier that vents to the outside of the boat if the pressure in the hot water system rises above a preset level.

[elessina]

I have an accumulator tank fitted downstream of my water pump, .... an ordinary red 8 litre accumulator tank from a plumbing shop quite cheaply which I'm going to T into the cold water feed pipe downstream of the one way valve. The only thing is it doesn't say whether it's for use with hot or cold water so does anyone know if it's ok, or do you need special accumulator for hot water systems?

I do not know if an accumulator is ok with hot water, but not quite sure why you are asking. If I read correctly, you are going to install it in the cold supply, after the non return valve situated prior to the input into the calorifier. And this sounds the right place.

 

I had a problem of the water coming out of the safety valve, when the calorifier was heated up when I first installed my system. I simply removed the non return valve, and have had no problem since. But another way (probably the right way, so as to stop any 'hot' water backing up the cold water supply) is to install a second accumulator, as you intend to do. But I can not imagine this getting very hot, unless it is very very close to the clorifier, and I do not see that it needs to be close to the calorifier.

 

Ian

Elessina

[John Orentas]

Can't see that there is any advantage to be gained in having two accumulators in a system.

[blackrose]

There is usually a pressure relief valve at the top of the calorifier that vents to the outside of the boat if the pressure in the hot water system rises above a preset level.

 

Yes, but I wanted to allow for a bit of expansion before this pressure is reached - it's a bit of a waste if your hot water ends up in the canal.

 

I do not know if an accumulator is ok with hot water, but not quite sure why you are asking. If I read correctly, you are going to install it in the cold supply, after the non return valve situated prior to the input into the calorifier. And this sounds the right place.

 

I had a problem of the water coming out of the safety valve, when the calorifier was heated up when I first installed my system. I simply removed the non return valve, and have had no problem since. But another way (probably the right way, so as to stop any 'hot' water backing up the cold water supply) is to install a second accumulator, as you intend to do. But I can not imagine this getting very hot, unless it is very very close to the clorifier, and I do not see that it needs to be close to the calorifier.

 

Ian

Elessina

 

Ok, I hadn't thought of that but surely the cold water feed downstream of the non-return valve is actually part of the hot water system? My non retun valve is only about 4ft away from the calorifier, meaning that the accumulator will have to be installed within this distance - say about 3ft from the calorifier. I'll check to see how hot this pipe gets before I install the tank

 

How do you stop hot water backing up your cold water pipe if you don't have a non-return valve? Woudn't an immersion heater for example, continue to heat the tank until hot water reached your water pump? I also heard (but I don't know if this is correct), that the non-return valve is there to prevent bacterial growth in the cold water pipe. But if this were true then what stops bacterial growth in the hot water pipes?

 

Can't see that there is any advantage to be gained in having two accumulators in a system.

 

The first accumulator next to the waterpump is there to regulate water pressure, the one I am going to install is there for an entirely different reason - to allow for hot water expansion.

Edited January 4, 2007 by blackrose

[dor]

Provided your calorifier is properly bled so their is no significant amount of air in it, you will not get much hot water backing up without the NRV. Whilst the system will pressurise due to the expansion, water is virtually incompressible, so only a tiny amount of water will come back if you say turn a cold water tap on without a NRV fitted.

 

Your system with the accumulator in the cold pipe just after the pipe should be fine, this will hold the pressure and when you turn a cold tap on, the pressure will be directed from there, not from your calorifier.

 

Most people find that once an accumulator is fitted, they get virtually no loss through the PRV on the calorifer.

Edited January 4, 2007 by dor

[Ernie]

"Yes, but I wanted to allow for a bit of expansion before this pressure is reached - it's a bit of a waste if your hot water ends up in the canal."

 

I have never experienced hot water venting from the relief valve and I do test the valve occasionally to make sure it has not seized up.

 

I don't have any non return valve in my system so I guess any expansion pressure is being handled by the accumulator?? I have also never noticed any warming of the cold water.

[DHutch]

...My non retun valve is only about 4ft away from the calorifier, meaning that the accumulator will have to be installed within this distance - say about 3ft from the calorifier. I'll check to see how hot this pipe gets before I install the tank

I wouldnt have thought the cold feed would at all hot 3ft from the calorifirer.

- We have a very simular setup at home with our imersion heater, the pipe is stone cold as it leaves the tank almost, deffonaty not hot enought to do any harm to the expantiontank/accumulator.

 

On the boat im pritty sure we just dont have the one-way valve! Which is the other was of doing it. Or putting up with the possablty of a tiny passing thought the PRV. (although makesure it is going overboard, or into the sterntube bildge or whater, some go into the cabin bildge, which is poor)

 

 

Daniel

[Keeping Up]

There is very very little expansion as the water heats up, but there will be some; presumably there is also a pressure increase as some of the dissolved gases attempt to break free. It will be partly offset by the fact that the copper calorifier tank also expands as it warms up. The pressure relief valve will often dribble slightly if you heat from very cold to very hot without drawing off any hot water during that time, and what you are suggesting would probably prevent that.

 

The NRV does prevent hot water getting back into the cold feed, but the amount that does so will be negligible. Like you I think the idea of bacterial growth is a red herring. From my experience the only time you get enough back-flow to be detected, is if you switch off the pump and then open both a high-level hot tap and a low-level cold tap at the same time. This was the viewpoint expressed my my boatbuilder, and it seems to make sense; it was on this reasoning that he actually fitted te NRV just after the tank (ie in its hot water outlet pipe rather than in its cold-water inlet). There can be no back-flow through it, so hot water from the tank cannot flow back into the cold system because this would create a vacuum in the tank (I know this works because if I want to drain the tank I have to let the air in to it). When everything heats up, any slight expansion may indeed push some hot water back down the cold pipe but it has never pushed enough to reach the cold tap that is 6 feet from it; it then slightly raises the pressure in the accumulator rather than dribbling out of the pressure relief valve.

 

Allan

[ChrisPy]

I'm doing exactly what blackrose suggests. 2 accumulators, one upstream and one downstream of the non-return valve in the calorifier feed line just downstream of the main pump. the upstream one protects the complete cold system, the downstream one protects the complete hot system, and I hope I never see the pressure saftey valve relieving itself.

[blackrose]

Thanks for all your responses. I'll check to see how warm/hot the cold water feed pipe to the calorifier gets after the NRV before Ting the accumulator in. Hopefully it will stay cold/warm and it won't be an issue.

[chris w]

There is very very little expansion as the water heats up, but there will be some

 

The expansion is about 4%. If you have a fairly typical 13 gallon calorifier (~60 litres) the water will therefore expand by about 2 litres in volume some of which will be wasted over the side through the PRV.

 

Since a (bladder-type) accumulator will only hold half its volume in water (the other half is pressurised air above the bladder) the accumulator needs to be about 8% of the volume of the calorifier or in round numbers say 10%. So a 60 litre calorifier would need a 6 litre minimum accumulator. The usual nearest standard size of accumulator is 8 litres which would therefore serve a calorifier up to about 17 gallons (80 litres).

 

Chris

[smileypete]

Anyway, a friend bought me an ordinary red 8 litre accumulator tank from a plumbing shop quite cheaply which I'm going to T into the cold water feed pipe downstream of the one way valve. The only thing is it doesn't say whether it's for use with hot or cold water so does anyone know if it's ok, or do you need special accumulator for hot water systems?

 

Probably intended for a central heating system so should be fine with hot.

 

cheers,

Pete.

[DHutch]

The expansion is about 4%. If you have a fairly typical 13 gallon calorifier (~60 litres) the water will therefore expand by about 2 litres in volume some of which will be wasted over the side through the PRV.

 

Since a (bladder-type) accumulator will only hold half its volume in water (the other half is pressurised air above the bladder) the accumulator needs to be about 8% of the volume of the calorifier or in round numbers say 10%. So a 60 litre calorifier would need a 6 litre minimum accumulator. The usual nearest standard size of accumulator is 8 litres which would therefore serve a calorifier up to about 17 gallons (80 litres).

 

Chris

And simuarly, our 210L hotwater cylinder in our house had a 22L expantion vessal...

 

 

Daniel

[ChrisPy]

The expansion is about 4%.

4% is on the high side. total expansion from freezing to boiling is 4.3%. For most of us we should see more than about 2% in practice.

[elessina]

How do you stop hot water backing up your cold water pipe if you don't have a non-return valve? Woudn't an immersion heater for example, continue to heat the tank until hot water reached your water pump? ....

I initially installed the non-return valve to stop hot water backing up the cold water pipe. But the safety valve would dribble whenever we turned the immersion heater on, or ran the boat engine. This because the hot water had nowhere to expand into, two options, install a second accumulator (as you intend to do) or remove the non-return valve. Removing the non-return valve was the simplest (and cheapest) solution.

 

Hot water backing up the cold pipe. During the summer I noticed a very small amount of 'warm' water coming out the cold water tap, this lasted for no more than 1 second. Now, in the winter, no warm water at all.

 

Suggestion, do not install the non-return valve or accumulator, and see how the system performs. I think it will be fine. But if you find hot water backing up the cold pipe, install the NRV and accumulator….. On the other hand you have already bought both, so will not save any money by not fitting them…. Choices!!!!!

 

Talking Non-return valves. A few months back our fresh water pump (Whale) kept on cycling on-off every hour or so. I installed a non-return valve just before the pump (between pump and strainer), cured the problem completely. We now always leave the pump on at night, and it does not cycle, in fact we can often flush the loo in the morning and there is still sufficient pressure in the system for the pump not to have to operate. If you have a spare non-return valve, it may be worth considering installing one prior to pump!!!!

 

Ian

Elessina

[blackrose]

I initially installed the non-return valve to stop hot water backing up the cold water pipe. But the safety valve would dribble whenever we turned the immersion heater on, or ran the boat engine. This because the hot water had nowhere to expand into, two options, install a second accumulator (as you intend to do) or remove the non-return valve. Removing the non-return valve was the simplest (and cheapest) solution.

 

Hot water backing up the cold pipe. During the summer I noticed a very small amount of 'warm' water coming out the cold water tap, this lasted for no more than 1 second. Now, in the winter, no warm water at all.

 

Suggestion, do not install the non-return valve or accumulator, and see how the system performs. I think it will be fine. But if you find hot water backing up the cold pipe, install the NRV and accumulator….. On the other hand you have already bought both, so will not save any money by not fitting them…. Choices!!!!!

 

Talking Non-return valves. A few months back our fresh water pump (Whale) kept on cycling on-off every hour or so. I installed a non-return valve just before the pump (between pump and strainer), cured the problem completely. We now always leave the pump on at night, and it does not cycle, in fact we can often flush the loo in the morning and there is still sufficient pressure in the system for the pump not to have to operate. If you have a spare non-return valve, it may be worth considering installing one prior to pump!!!!

 

Ian

Elessina

 

So you're basically using the cold water pipe (+ calorifier itself) to allow for expansion. My NRV is already in so I may as well fit the accumulator. Although I've had no problems so far I was warned by two different people and it seems sensible to prevent the possibility of a cracked calorifier because the pressure release valve seized or failed to work properly.

 

Sounds like your Whale pump was allowing pressure to fall upstream of it causing it to cycle. Why does this happen? I'd have thought the pressure upstream of the pump from the weight of the water in the tank was fairly constant? My Sureflo pump is on all night & doesn't cycle unless there's a leak.

 

I've got into the habit of always switching it the pump off when I go out and I installed a cheap switch so as not to wear out my trip switch panel. The number of times I've seen flooded boats... (ok it's only 3 or 4). It's never a leak from outside, but fresh water that you've brought onboard that hasn't stayed where it was supposed to. Also if you inadvertantly ran your tank dry and your pump kicked in while you were out, your pump would burn itself out.

[John Orentas]

Talking Non-return valves. A few months back our fresh water pump (Whale) kept on cycling on-off every hour or so. I installed a non-return valve just before the pump (between pump and strainer), cured the problem completely. We now always leave the pump on at night, and it does not cycle, in fact we can often flush the loo in the morning and there is still sufficient pressure in the system for the pump not to have to operate. If you have a spare non-return valve, it may be worth considering installing one prior to pump!!!!

Ian

Elessina

 

 

If the water pump is cycling it may well indicate you have a leak somewhere, far better to fix the leak rather than fitting a non return valve, the leak may still be there.

I knew a chap who had an old coach, the low air pressure air brake light insisted on coming on, he took the bulb out and solved the problem.

On principle it is a good idea to avoid the use of non return valves, they can cause 'locking in' of pressures and prevent draining down if ever required.

[blackrose]

If the water pump is cycling it may well indicate you have a leak somewhere, far better to fix the leak rather than fitting a non return valve, the leak may still be there.

I knew a chap who had an old coach, the low air pressure air brake light insisted on coming on, he took the bulb out and solved the problem.

On principle it is a good idea to avoid the use of non return valves, they can cause 'locking in' of pressures and prevent draining down if ever required.

 

Ian's NRV is fitted upstream of his pump so a leak downstream would not prevent the pump from cycling.

 

If there were a leak upstream of the pump wouldn't that just be replaced by more water from the tank & keep the pressure constant? I think what's happening in Ian's case is that for some reason water is gradually moving from the downstream side of the pump back through the pump causing a loss in downstream pressure & the pump to cycle. The NRV he has fitted is now stopping that from happening.

 

I have been woken up on a couple of occasions when my pump which is under the bed, suddenly went off in the middle of the night. I searched everywhere for a leak and eventually realised that the hot water in the calorifier had cooled down during the night causing a drop in pressure and enabling the pump to cycle.

Edited January 5, 2007 by blackrose

[John Orentas]

I have been woken up on a couple of occasions when my pump which is under the bed, suddenly went off in the middle of the night. I searched everywhere for a leak and eventually realised that the hot water in the calorifier had cooled down during the night causing a drop in pressure and enabling the pump to cycle.

 

 

That's why I said, it 'may well' indicate you have a leak somewhere, if the valves within the pump allow passsge of water it will show the same symptom though without the leak. The principle still holds however, if it is a Sureflo a strip and clean with usually cure the problem.

[blackrose]

That's why I said, it 'may well' indicate you have a leak somewhere, if the valves within the pump allow passsge of water it will show the same symptom though without the leak. The principle still holds however, if it is a Sureflo a strip and clean with usually cure the problem.

 

I wasn't disputing what you said John. Of course if your pump cycles without a tap being turned on your first suspicion should be that you have a leak. However the NRV that Ian has fitted is upstream of the pump so will make no difference to this possibility one way or the other. If fitting the NRV stopped the pump cycling then it the cycling definately wasn't caused by a leak downstream of the pump and probably not upstream either.

Edited January 5, 2007 by blackrose

[Split Pin]

Unless I have missed it somwhere no one has mentioned that if the accumulater is a bladder type then the pressure above the bladder needs to be adjusted to less than the system working pressure. Normally by approx 2 psi. If not the the accumulater won't do any thing wherever you put it.

 

Just been looking at mine temperature rating is -10C to +99C made by Hotpot, Bladder type

Edited January 5, 2007 by Split Pin

[John Orentas]

I wasn't disputing what you said John. Of course if your pump cycles without a tap being turned on your first suspicion should be that you have a leak. However the NRV that Ian has fitted is upstream of the pump so will make no difference to this possibility one way or the other. If fitting the NRV stopped the pump cycling then it the cycling definately wasn't caused by a leak downstream of the pump and probably not upstream either.

 

 

Don't follow your reasoning there but I won't pursue it.

[blackrose]

Don't follow your reasoning there but I won't pursue it.

 

Well, think about it. THe NRV is positioned upsteam of the pump, therefore it only prevents water from going backwards. Water can still go forwards and in the event of a leak it will still leak and still cause the pump to cycle. Therefore, if there is a leak it will make no difference one way or the other.

 

All the NRV is doing in Ian's case is preventing watyer from backing up through the pump and creating a pressure drop on the downstream side. He hasn't installed it to stop a leak.

[DHutch]

I have to admit, im with blackrose on this one john.

- Ians NRV is simply backing up the oneway valves within the pump itself.

- We of cause do exactly the same with our boiler feed pumps. (although the nrv are just after the pump, rather than just before)

 

 

Daniel