Expansion vessel

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Mike
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Expansion vessel

Post by Mike » Wed Oct 31, 2018 5:19 pm

Its time to change my domestic hot water tank, as in all things French its at mains pressure, my existing tank does not as far as I know (could be internal) have an expansion vessel, the tun-dish discharges through a wall into the garden and the ground is generally damp in that location, so the new DHW tank will have an expansion vessel fitted, Now the question: I have been looking at various installations and the vessel seems to be either on the cold or hot side, I know the theory of each, i.e. fitting on the cold side due to the heating of the water pushing the suppled water back due to expansion, this is fine unless a non return valve is fitted, then fitting the vessel on the hot side is the only alternative, I think I just answered my own question. :roll: I assume it does not matter where the vessel is fitted as long as its close to the tank on the supply pipe, height would also seem to be irrelevant to its operation, hmmm its good to talk these things through.

Mike

michael86
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Re: Expansion vessel

Post by michael86 » Wed Oct 31, 2018 6:51 pm

Hi Mike,

The expansion vessel should go on the cold supply side between the groupe de securite and the chauffe-eau. You will need to fit a 3/4 inch tee to do this. The non-return valve is in the groupe de securite. There is a diagram showing connections on this page:
https://blog.elyotherm.fr/2013/05/vase- ... n-ecs.html
There will probably be a connection diagram with the new chauffe-eau also.

It is regulation now to also fit a mitigeur thermostatique (thermostatic mixing valve) to limit the temperature of the outgoing hot water. It shows the connection on the diagram in the link. I didn't want one when I fitted our new chauffe-eau as I like to be able to top up my bath with really hot water. If the police come round I will know someone on this site has reported me.

Michael

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RobertArthur
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Re: Expansion vessel

Post by RobertArthur » Wed Oct 31, 2018 9:56 pm

Mixchael86, even the French legislator tries to respect the principle that ex post facto (retroactive) law should be avoided. It goes for the regs in the newest version of the French electrical code: date of construction/installation/Consuel attestation is the minimum. Old house: yesterday's regs, new builds, today's regulations. So I do hope that the plumbing authorities took note of this principle.

About these regs, let's have a look at their content. Does the French law prescribe the (in)famous mitigeur? Room for interpretation in my opinion - correct me if I'm wrong. I read the following in this Arrêté du 30 novembre 2005:

1. Afin de limiter le risque de brûlure :
- dans les pièces destinées à la toilette, la température maximale de l'eau chaude sanitaire est fixée à 50 °C aux points de puisage ;
- dans les autres pièces, la température de l'eau chaude sanitaire est limitée à 60 °C aux points de puisage ;
- dans les cuisines et les buanderies des établissements recevant du public, la température de l'eau distribuée pourra être portée au maximum à 90 °C en certains points faisant l'objet d'une signalisation particulière.


A thermostatic mixer tap with a lock button does a good job in limiting the temperature to a max of about 38 degrees, safe for little children, below the 50 degrees as mentioned in the regs. In case of emergency break glass, unlock and start topping up your bath. Department technicalities: thermostatic mixer taps like to see a fair amount of difference between input and output temperatures. Lowering the input temperature- hello Salmonella - is not always a good idea.

Expansion vessel: not (yet) in the regs, see this EDF information.

I'm not unbiased in this discussion I'm afraid. More than one road leads to Rome.

vic evans
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Re: Expansion vessel

Post by vic evans » Wed Oct 31, 2018 10:24 pm

Whilst recognising the reason for fitting an expansion vessel on a French system it is not subject to the same bye-laws as in the UK which are designed ,amongst other things, to prevent the 'waste' of water.
Personally I prefer the occasional drips from the group safety valve which keep the trap on the stack connected syphon topped up & stop smells. This way I know the valve has been 'exercised' & should do it's job & open in the unlikely event of over pressure.

Mike
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Re: Expansion vessel

Post by Mike » Wed Oct 31, 2018 11:14 pm

Thanks for your input guys and the diagram's I knew I could rely on you all for sensible answers.

mike

Mike
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Re: Expansion vessel

Post by Mike » Thu Nov 01, 2018 11:26 am

Further to my first post, it seems that the only place to fit an expansion tank on a new installation is on the cold feed, this is due to the fairly new requirement for the thermostatic mixing valve which compromises the route for expanding water on the hot side, which to my way of thinking the hot side is the obvious place to put it, but then this is France.

Mike

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Re: Expansion vessel

Post by Fitter » Thu Nov 01, 2018 11:43 am

Mike wrote:
Thu Nov 01, 2018 11:26 am
Further to my first post, it seems that the only place to fit an expansion tank on a new installation is on the cold feed, this is due to the fairly new requirement for the thermostatic mixing valve which compromises the route for expanding water on the hot side, which to my way of thinking the hot side is the obvious place to put it, but then this is France.

Mike
The expansion vessels have a diaphragm inside them, separating the air pressure from the water. Perhaps the diaphragm doesn't last long if fitted on the hot side?
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Re: Expansion vessel

Post by RobertArthur » Thu Nov 01, 2018 11:57 am

Mike, the expansion vessels for sale here in France don't have any insulation, so the hot side is not the obvious place to put it if you want to minimise heat loss.

Mike
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Re: Expansion vessel

Post by Mike » Thu Nov 01, 2018 3:03 pm

I do understand all that, its just that it goes against the grain that the expanding water is used to force cold water into what is after all and expansion tank.

Again thanks for all your thoughts.

Mike

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