On 21/01/2011 17:17, Ronald Raygun wrote:
Lobster wrote:

On 21/01/2011 13:00, John Rumm wrote:
On 20/01/2011 22:12, Roger Mills wrote:
On 20/01/2011 21:23, Ron Lowe wrote:

P5 says the pre-charge pressure on the expansion vessel should be 4
bar.

THe 6 bar reference on P14 is the cracking pressure of the Expansion
Relief Valve.

Pump the thing up to 4 bar cold.


.. . . making sure that the 'wet' side isn't under pressure while you do
so.

which probably means shut off the mains inlet, and open a hot tap...

I assumed I'd need to open a drain cock on the CH to reduce the pressure
to zero, thereby losing all that precious inhibitor - is that not the
case?

No.

There are two distinct pressurised hot water circuits, each with their own
expansion vessels and pressure relief valves. One circuit is for the water
which circulates through boiler, radiators, and the heating coil inside the
HW cylinder, and its EV and PRV are usually located inside the boiler
housing. This is the water which has your inhibitor in it.

Update...

Well the expansion vessel was completely devoid of any pressure at all,
but at least there was no water leaking out so no probs with the
diaphragm. I then discovered a slow (air) leak on the Schraeder valve
so have replaced the valve core, and it seems to be holding OK so far.

Wasn't able to get more than 2.4 bar into the vessel using my footpump
against the wall at chest height - likely to be a problem? Bloody hard
work towards the end (yes the system was depressurised as direct!) -
should it be that difficult? Will it matter not getting to 4 bar?

I'd like to have replaced the whole valve not just the core. However: on
top of the vessel, the valve body is held in place by a retaining nut
(just as it would be on a bicycle tyre). It was easy to loosen the nut,
but it was clear to me if I removed it completely I'd just lose the
valve body for good down inside the expansion vessel! So didn't go
there... are these things supposed to be serviceable? Can the vessel be
dismantled to get at the innards, or will it be a bin job for the whole
vessel if my new core still doesn't work?

(It's a Varem 19-litre white - potable - vessel by the way, in case that
helps)

David