On Tue, 02 Dec 2008 16:49:03 +0000, Tim Downie wrote:

John Rumm wrote:
Tim Downie wrote:

If you buy a good quality cylinder (I'm going to get an Oso) and have
the appropriate safety ancillaries installed I can't see the point in
wasting time and money on an annual inspection by someone who has
gone on a 0.5 day "course".

It's still a pressure vessel with explosive potential (more so than a
vented cylinder). Safety ancillaries can and do fail. May not be
hard to check yourself if you know what you're doing but I'm not sure
I'd want to live on the other side of a party wall to one that hadn't
been inspected for years. For most non-DIYers, annual inspection
probably makes sense.

I think there is another misconception here as well. The only time a
pressurised water cylinder is at explosion risk is going to be when it
has the possibility of being heated to over the boiling point of the
water content. Then there is the risk of the explosive production of
steam should it rupture.
For a cylinder heated via a water flow from a boiler, the chances of
super heating it seem minimal.

You're forgeting Sods law. The only time the safety valve is likely to
get stressed is when your CH boiler packs up on Christmas Eve and you
turn on the immersion element that's not been used in years. A sticky
stat in that and a sticking safety valve can then lead to an explosive
situation. A vented cylinder needs another level of system failure
before it can blow.

The risk is low but it's a hgher risk than an vented cylinder.

That'll need TWO sticking stats for the immersion heater and TWO sticking
relief valves, one of which has two means of opening.


--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at http://www.diyfaq.org.uk
Gas fitting FAQ http://www.makewrite.demon.co.uk/GasFitting.html
Sealed CH FAQ http://www.makewrite.demon.co.uk/SealedCH.html
Choosing a Boiler FAQ http://www.makewrite.demon.co.uk/BoilerChoice.html