Unvented Cylinder explosion...

The first thing it would do is push the mains water back down the pipe back into the mains suupply. Mains pressure is normally about 16 bar, these tanks explode at about 300 bar, so not much chance of it ever happening. Also, a lot of pipes leading from hot water tanks in modern houses are made of plastic, the pressure would go through to these and they would blow or become disconnected long in advance of the tank exploding. The only way I can see of doing it would be to totally block off all the pipes leading into the tank with a very secure blanking cap.

 

That's a very good point.

 

hi
not quite right?
check valve?
16 bar mains? i don't think so..

if the hot distribution pipe came adrift with 110 c water in the cylinder, it would potentially rapidly expand the volume of water to steam.
we know this can happen so we install with extra safety measures.

regards
peter

 

This is why i prefer vented cylinders - 2 main reasons: 1. Safety (BRE did some experiments some years ago into explosions in unvented cylinders and I was on site when they blew one up - not for the faint hearted) 2. Domestic hot water from a two coil vented comes fresh straight from the mains - mains pressure and no hanging about for days on end in a hot tank.

diymostthings

 

One question. While I understand that it "could" happen on a direct, Am I correct in thinking it would be impossible to happen on an indirect heated one?

 

Regarding vessels exploding google BLEVE and see what it brings up, a BLEVE in tech speak is a Boiling Liquid Expanding Vapour Explosion.They can be quite dramatic as well as extremely damaging/dangerous.

https://search.yahoo.com/yhs/search?hspart=mozilla&hsimp=yhs-006&ei=utf-8&fr=ytff1-tyc&p=bleve video&type=

I know the above is a gas cylinder,but even steam can be just as destructive.

 

I accept things can go bang, this is a video of circuit breakers blowing up panels

But we can't get away from the fact everything could be dangerous if it's safety features are disabled. See how you get on in an accident if you disable the seat belts, airbags etc

 

I agree with you,however personally I think cars would be safer without airbags,as a copper said "replace drivers airbag with a spike".There are so many idiots driving dangerously today because "if I have a crash I've got airbags", mind you it's the same with electrics,people mess with them nowadays because "if I get it wrong that thing in the box will trip".Safety features such as those above are ok as safety features,sadly a lot of people use them as an excuse for stupid or dangerous behaviour.

 

The explosions can only happen on unvented - almost by definition! But as said the risk is miniscule (but why take it?)

diymostthings

 

So Just to be clear, on an indirect heated cylinder where the heat input was say 80C from the boiler, you can get it to boil water? Are you sure? I can't see how it could possibly get hotter than the input, since if somehow it could, it would actually lose heat to the coil, since heat transfer is hot > cold