Sealed system expansion vessel question(s)

12 May 2009
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United Kingdom
Hello-I have some questions please about an expansion vessel that I'd like help with if anyone is willing to?

When buying an expansion vessel do you have to buy one of the correct charge/ or is there a range available for your to charge it? What I mean is:

If i buy a 12 litre vessel and my system requires a 0.5 bar charge, is a normal/standard 12 litre vessel ok? or do i need to be more specific, ie is there 12litre vessels available with 0.5 bar 1 bar and 1.5 bar pressure ranges? (or can you get the correct litre size and charge it to your own requirement)?

Thanks for helping, sorry if i sound confusing....
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Thanks for replying.

a few more questions regarding the vessel if i may:

is it ok to overcharge a vessel slightly, so if the static head in my system is just 0.2 bar then a 0.5 bar pressure charge is OK??

what happens if the vessel is over or under charged or in fact over or under sized? i am guessing a prv relief?

thanks for helping my confused head!
The pre-charge pressure is in the boiler manufacturers manual, a bit over don't matter.

Just in case, there are different vessels for heating, hot water, and boosted water.
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Thanks for helping me with my 2 posts guys.

The vessel i have is in the airing cupbaord. it says on it 12litres. doesn't say an exact charge pressure.

would it be dangerous to not charge it correctly, say if i overcharge or undercharge the new 1?
i read that for every 1 metre of static head from the vessel to the highest rad (so in my case 2 metres) 0.1 bar pressure is the charge. So 0.2 bar should be the charge pressure. but as you have told me kindly, a little over is ok. if i charge it ip to 0.5 bar or even 1 bar is that ok too?
for a domestic property is there like a rule of thumb for the size of the vessel and charge range? thanks for all your help. all the best.
Yes the rule of thumb is whatever it says in the boiler manufacturers instruction manual
i get ya, but my vessel is not in the boiler and i don't even have the boiler manual. it looks like it was added after if that makes sense???.....
But it's connected to it, albeit remote.

Whats the make and model.
potterton flamingo II RS50 it says. i think there was an older header tank before connected to the system but replaced by vessel before i moved in.

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