Hot water expansion tank

[blackrose]

Does anyone know where I'd get a hot water expansion tank for my calorifier? My 5 year old one sprang a leak last night. I suspect it wasn't for fresh water and it's corroded inside. So, this has got me thinking: Is my accumulator tank that I bought from Uxbridge Boat Centre going to be ok, or are they different because they do hot and cold water?

 

I think the hot water expansion tank came from Screwfix.

Edited December 7, 2012 by blackrose

[bizzard]

If i had a calorifier i'd mount it in a big plastic tray for ready when the thing springs a leak.

[Guest]

If i had a calorifier i'd mount it in a big plastic tray for ready when the thing springs a leak.

Whilst it is nice to have "free" hot water off the engine, come the day when my calorifier inevitably bursts, I will be replacing it with an instantaneous gas water heater like on my previous boat.

[BEngo]

Does anyone know where I'd get a hot water expansion tank for my calorifier? My 5 year old one sprang a leak last night. I suspect it wasn't for fresh water and it's corroded inside. So, this has got me thinking: Is my accumulator tank that I bought from Uxbridge Boat Centre going to be ok, or are they different because they do hot and cold water?

 

I think the hot water expansion tank came from Screwfix.

The one you got from UBC will be fine, as in the short-term would another from Screwfix. Nearly all accumulators/expansion tanks are a rubber bladder in a watertight steel 'box'. (Charlie Fox used to use magnum sized wine bottles mounted neck-down IIRC and Jabsco did something similar in plastic.) The difference between the expansion tanks is whether the 'box' bit is coated/stainless steel to prevent rusting or whether the protection relies on anti-corrosion agents in the water. In your case you need one that's coated i.e. marked/sold "for potable water" because that's what your hot water started out as.

 

N

[Guest]

Does anyone know where I'd get a hot water expansion tank for my calorifier? My 5 year old one sprang a leak last night. I suspect it wasn't for fresh water and it's corroded inside. So, this has got me thinking: Is my accumulator tank that I bought from Uxbridge Boat Centre going to be ok, or are they different because they do hot and cold water?

 

I think the hot water expansion tank came from Screwfix.

I have one from there, and it too is rusting internally. There were some on ebay suitable for potable hot water when I looked recently. Thanks for the reminder

[Mac of Cygnet]

I don't have a hot water expansion tank. Isn't that what the pressure relief valve's for?

[bizzard]

Whilst it is nice to have "free" hot water off the engine, come the day when my calorifier inevitably bursts, I will be replacing it with an instantaneous gas water heater like on my previous boat.

Indeed, I wouldn't swop my Paloma for all the beer in Hertfordshire.

[Guest]

I don't have a hot water expansion tank. Isn't that what the pressure relief valve's for?

Yes- and no. That is a pressure release device to release pressure if things get out of hand. I am told it is also unkind to the calorifier to let this amount of pressure build up. The extra vessel absorbs the build up of pressure, without losing several litres of water overboard during a days cruise (only to lose the same amount of water later, when waiting for the hot water to appear at the tap )

It just seems a more civilised way of doing the job to me (using a vessel.)

That said, I ran for several years before I got around to fitting a vessel.

[nb Innisfree]

I don't have a hot water expansion tank. Isn't that what the pressure relief valve's for?

 

PRVs withiut an expansion tank have a tendency to weep.

[Guest]

PRVs withiut an expansion tank have a tendency to weep.

I have seen that happen too.

[blackrose]

I don't have a hot water expansion tank. Isn't that what the pressure relief valve's for?

 

It depends. If you have a non-return valve in the cold feed pipe to that calorifier (to stop hot water expanding up the cold pipe), then you should have a hot water expansion tank because otherwise the expansion has nowhere to go and will bleed out the pressure relief valve. That relies on the PRV working - if it gets stuck then you have a pressure vessel! A weeping PRV also wastes hot water. If on the other hand you don't have a NRV in the cold feed pipe then you can get away without an expansion tank.

 

I went an bought an 8 litre accumulator tank with stainless inside from Uxbridge that I'll fit as a hot water expansion tank (set to 3 or 4 psi above the pump's cut out pressure). It was 43 quid but that was cheaper than the plumbers merchants.

 

Indeed, I wouldn't swop my Paloma for all the beer in Hertfordshire.

 

Nor would I.

 

I have a calorifier and an instant gas water heater. Why would one have to swop?

Edited December 8, 2012 by blackrose

[Mac of Cygnet]

The extra vessel absorbs the build up of pressure, without losing several litres of water overboard during a days cruise (only to lose the same amount of water later, when waiting for the hot water to appear at the tap )

 

I have a 50litre (I think) calorifier. If the water is heated from (say) 10deg to 60deg in a day's cruising, then the water volume will increase by rather less than 1 litre (I've checked this using coefficient of expansion).

 

So the PRV will release less than one litre into the bilge (which is where it goes). I'm quite happy with that. Not a great waste.

[system 4-50]

I have a 50litre (I think) calorifier. If the water is heated from (say) 10deg to 60deg in a day's cruising, then the water volume will increase by rather less than 1 litre (I've checked this using coefficient of expansion).

 

So the PRV will release less than one litre into the bilge (which is where it goes). I'm quite happy with that. Not a great waste.

but such an inelegant solution

 

 

 

[blackrose]

I have a 50litre (I think) calorifier. If the water is heated from (say) 10deg to 60deg in a day's cruising, then the water volume will increase by rather less than 1 litre (I've checked this using coefficient of expansion).

 

So the PRV will release less than one litre into the bilge (which is where it goes). I'm quite happy with that. Not a great waste.

 

I wouldn't be the litre of hot water I'd worry about wasting, it would be the PRV not working...

 

As I said, if you have a NRV in the system then you have a pressure vessel. If the PRV ever fails then the expansion may rupture the calorifier.

[Guest]

The main reason for my fitting the expansion vessel, was on the recommendation from the maker of the calorifier (mine has NRV on cold feed.) Unfortunately I bought the wrong type.

 

see p7 two expansion tank setup with NRV:

 

http://www.jabscoshop.com/itemimages/C-Warm%20Selection%20Guide.pdf

Edited December 8, 2012 by Guest

[Guest]

I wouldn't be the litre of hot water I'd worry about wasting, it would be the PRV not working...

 

As I said, if you have a NRV in the system then you have a pressure vessel. If the PRV ever fails then the expansion may rupture the calorifier.

That is my take on it. I see the PRV as a safety device, rather than a working solution to pressure build-up. I know plenty of people who don't bother with the second vessel (didn't myself for some time), but I feel happier with one fitted.

Edited December 8, 2012 by Guest

[PaulD]

It depends. If you have a non-return valve in the cold feed pipe to that calorifier (to stop hot water expanding up the cold pipe), then you should have a hot water expansion tank because otherwise the expansion has nowhere to go and will bleed out the pressure relief valve. That relies on the PRV working - if it gets stuck then you have a pressure vessel! A weeping PRV also wastes hot water. If on the other hand you don't have a NRV in the cold feed pipe then you can get away without an expansion tank.

 

I went an bought an 8 litre accumulator tank with stainless inside from Uxbridge that I'll fit as a hot water expansion tank (set to 3 or 4 psi above the pump's cut out pressure). It was 43 quid but that was cheaper than the plumbers merchants.

 

 

 

Nor would I.

 

I have a calorifier and an instant gas water heater. Why would one have to swop?

 

When checking / setting the pressure in the expansion tank should you do it with the water in the system up to pump cut out pressure i.e. with taps closed and after the pump has cut out or at ambient (outside air) pressure i.e. with the taps open?

 

I think it doesn't make any difference because the pump / gauge is just measuring pressure in the bladder above ambient? Correct?

 

Paul

[Guest]

When checking / setting the pressure in the expansion tank should you do it with the water in the system up to pump cut out pressure i.e. with taps closed and after the pump has cut out or at ambient (outside air) pressure i.e. with the taps open?

 

I think it doesn't make any difference because the pump / gauge is just measuring pressure in the bladder above ambient? Correct?

 

Paul

I pressurised my (hot water)expansion tank prior to pressurising the system. I am not saying this is correct procedure, but it worked OK for me.

[trackman]

Our original calorifier had no expansion vessel and its PRV never leaked any water. As far as I recall it had a non return valve in the cold supply.

 

However, earlier this year it failed, perhaps not surprisingly? I replaced it with one of the same type as changing all the pipework to suit a different model was not a task I fancied.

 

The manufacturer (Surecal) now recommends fitting an expansion tank, which I have done. They say this is because there have been too many failures of units where no expansion tank had been fitted.

 

Ironically the new setup leaked from the PRV every time we ran the engine! Recently I've had a play with the pressure in the expansion tank. It was factory set far too high, I found. Since I cut the pressure to 5 psi above the water pump cut out pressure, the weep from the PRV appears to have ceased.