Expansion vessels and charges

[Matt0029]

What causes an expansion vessel to loss it's charge and at what rate would you expect it too? Thanks

 

[cjg]

i have known expansion vessels to fail after 2-3 years and others to last over 10. Sometimes pressure loss is due to leaking shreider valves it's a mystery sometimes why they have lost it, but it's a simple job to recharge the expansion vessel.

 

[oz-plumber]

Maybe they have never been charged correctly.
Whenever I change an expansion vessel I always check the pressure.
I always check the pressure of an expansion vessel on a new boiler. You would be surprised how many are undercharged.
Probably due to temperatures of where the expansion vessel is charged.

 

[Matt0029]

Do they lose there charge as slowly the nitrogen gas they are charged with passes through the membrane? Oxygen finds it easier to pass through so they are originally charged with nitrogen. I read this somewhere.

 

[Knappers]

There would be some exchange I guess but mostly due to leakey valves and split bellows I think.
A little silicone grease in the schrader valve when topping up is a standard procedure for me now