On Fri, 20 Aug 2010 20:32:11 +0100, dennis@home wrote:

"VAG_dude" wrote in message
...
On 20 Aug, 19:33, Heliotrope Smith wrote:
VAG_dude wrote in news:bd4932e4-0e04-473a-a550-
:

When you re-pressurise an expansion vessel in a boiler are you
supposed to leave the drain cock open once you have got the pressure
to 0 bar ?

It does not matter if the drain cock is open or closed when pressurising
the expansion vessel as long as there is zero pressure
in the system whilst this operation is carried out.

--- news://freenews.netfront.net/ - complaints: ---

Cheers, turns out I had read a rather confusing guide!

Sorry but it does matter.
When you pressurise the expansion cylinder you want to leave it empty of
water, if you pressurise it while full of water there will be no room for
expansion afterwards.

That is if the system is full of water but at zero pressure the expansion
vessel may still be full of water (there is nowhere for it to go), when you
start to pump in air the pressure will go up but still leave no space for
expansion.

You do need to ensure there is somewhere for the water that may be in the
expansion vessel to go and that is the drain.

Yes, that's what I wondered, otherwise one is trying to compress water!
--
Peter.
The gods will stay away
whilst religions hold sway