CH expansion vessel. How does it work?

[wedge69]

No problem, just curious.

If I have a sealed central heating system with the expansion vessel charged at 1.5 bar, what actually happens? When the system is on and heating and reaches 1.5 bar, does the expansion vessel allow more room for the water expansion and hence keep the system pressure constant?

I guess what I am asking is what is the relevance of the vessel charge?

Thanks

 

[Piers1989]

No problem, just curious.

If I have a sealed central heating system with the expansion vessel charged at 1.5 bar, what actually happens? When the system is on and heating and reaches 1.5 bar, does the expansion vessel allow more room for the water expansion and hence keep the system pressure constant?

I guess what I am asking is what is the relevance of the vessel charge?

Thanks

You're about right...

When water is heated up it expands, so in a sealed system the volume of water is X (whatever it can hold cold at a certain pressure). When that water is heated up and it expands, its volume becomes Y so the expansion vessel is there to take the extra capacity.

Calculations can be done to work out volumes etc.

 

[wedge69]

So let's say cold pressure is X and ev is charged at Y. When ch comes on, at the point pressure reaches Y the expansion vessel starts to take the excess volume?

 

[Blagard]

I guess what I am asking is what is the relevance of the vessel charge?

To balance the pressure in the CH system. If not charged the internal rubber diaphragm would be pushed over until the air pressure in it reached what the CH heating system is charged at. That might leave no room for the expansion of the hot water.

The EV starts to take up some expansion as soon as the water is heated

It might help if you read the FAQ

//www.diynot.com/forums/plumbing/faqs.37170/