Reentrant wrote:
Tim Downie wrote:
fred wrote:
In article , Tim Downie
writes
John Rumm wrote:
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.
So, just to summarise, for an unvented cylinder to be at risk of over
pressure failure following oveheating:
a) The immerser must be in use and the stat fail
and
b) The manditory overheat stat must fail
and
c) The manditory over pressure relief valve must fail
Still scared?
Not terribly, no. Never was. But, all those things can fail
silently and the first you might know of their failure is when your
cylinder explodes. Of course it's rare and the Americans and
continentals have been using unvented electrically heated cylinders
for years and we don't hear of massive numbers of incidents.
It just cannont be denied that an open vented cylinder is
intrisically less dangerous than a pressurised one. If I had one or
lived next door to one I'd sleep easier knowing that somebody
competant who understood the dangers had periodically checked the
safety relief valve.
Tim
Not really the same but this is what happened when the Mythbusters
deliberately disabled all the safety features on an American-style water
heater:
http://www.youtube.com/watch?v=ekEHfihiNz4
I did like that episode made me smile not as good as the "clean out
cement mixer with dynamite" for a big bang
http://uk.youtube.com/watch?v=LIPprUxFap8
--
Kevin R
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