cylinder collapse.

sitja · 23-12-2010 6:37pm #1

Hi guys,

Might seem a silly question to some but just want to know if a dhw cylinder implodes can it still be used?? Obviously if it appears there are no leaks. Got a call today as this has happened some one i know..

From what i gathered there feed and expansion froze and had heating on so bang.. But when talking to them and they shut off the heating they said the dent popped back out.. So that makes me ask the question or does the cylinder definetly need to be changed?

Buford T Justice · 23-12-2010 6:48pm

sitja wrote: »

Hi guys,

Might seem a silly question to some but just want to know if a dhw cylinder implodes can it still be used?? Obviously if it appears there are no leaks. Got a call today as this has happened some one i know..

From what i gathered there feed and expansion froze and had heating on so bang.. But when talking to them and they shut off the heating they said the dent popped back out.. So that makes me ask the question or does the cylinder definetly need to be changed?

Are you saying that the cylinder collapsed inwards? I doubt the F&E Tank freezing would have caused that. The main volume of water is domestic hot, and only a coil linked to the F&E Tank.

sitja · 23-12-2010 6:53pm

as far as im aware yeah- they say it buckled in. Correct myself- not the f&e tank, but if the water supply cistern feed to cylinder freezes and the expansion off cylinder freezes and assuming they drew water from tap this would cause it to implode.

Sparkpea · 23-12-2010 11:33pm

yeah thats right - it could have caused that

if theres no leaks then in the short term its still ok to use it, in the long term i would change it asap (or shortly after christmas or when better weather picks up) as its likely to leak at some stage - no idea how long it could last

sitja · 23-12-2010 11:41pm

I have seen it and its a very little dent very unlikely to leak. One thing that baffles me is that they have claimed that they did not draw water from any hot tap??? so how exactly would it cave in then??

Sparkpea · 23-12-2010 11:45pm

it doesn't make sense really - when was the last time this person had their heating on? is it frozen as well?

if the tank in the loft freezes ok thats one thing, but for it to implode the dome of the hot tank then the hot tank would need to freeze also imo. it sounds like someone has connected the mains to it and tried to blow an airlock/ice out of it - even at that its only ever happened to me once.

sitja · 24-12-2010 1:18am

it happened while heating was on- that was working. it was off a whole day before that, noone was at it either im told.

chuck eastwood · 25-12-2010 11:14am

If the tank empty's due to frozen supply pipes the heating will still work as its a seperate circuit but the water to your hot tap will have gone meaning there is water passing through the coil in the tank but the tank itself is empty. the air in the tank will expand due to the heat from the coil. When the heating goes off the tank will contract basiacally causing a vacum due to a one way expansion / overflow valve not letting the air into the system. I wouldnt start the heating again unless you can be sure there is water in the tank and its not leaking

sitja · 25-12-2010 1:11pm

so ya the heating will work but will also cause the cylinder to implode as of the reason you stated, thanks, i genuinely didnt think it would implode unless the feed to it and expansion were blocked and some one drew from a hot water tap.

Buford T Justice · 25-12-2010 4:59pm

chuck eastwood wrote: »

If the tank empty's due to frozen supply pipes the heating will still work as its a seperate circuit but the water to your hot tap will have gone meaning there is water passing through the coil in the tank but the tank itself is empty. the air in the tank will expand due to the heat from the coil. When the heating goes off the tank will contract basiacally causing a vacum due to a one way expansion / overflow valve not letting the air into the system. I wouldnt start the heating again unless you can be sure there is water in the tank and its not leaking

The Cylinder wouldn't empty if the water is gone from the tank upstairs. The tank is filled from the bottom and drained from the top, so if there's no pressure pushing the water it'll just sit there. Its highly unlikely that the water was gone.

Also, in the same way that water can expand via the OSV, the air would expand in the same way and also contract.

For this to have caused a collapse you would need a partial vacuum in the cylinder in the first place and it would need to be completely sealed to keep the air inside. When air expands contracts it becomes the same volume again after contraction as would have been in the cylinder in the first place so I don't see that this is what caused it.

sitja · 25-12-2010 5:08pm

well i certainly think the cylinder had lost its water inside as i now witnessed the tank implode, it goes when the heating is left on for awhile cylinder starts to close in turned it off and bam pops back out. very strange. love to know how it actually drained the water out.

Buford T Justice · 26-12-2010 12:18pm

You've got me on that one. Unless someone actually physically drained the cylinder, then I Can't see how it would be empty.

sitja · 26-12-2010 2:21pm

Ya i am also quite confused by the matter. All i do know is that both feed and xpansion from the cylinder were frozen. I know it certainly wasnt drained purposely by anyone in the house. But the fact is it had to be empty because it imploded. How does a cylinder empty without obviously draining from the draincock or siphoning it out?

Sparkpea · 26-12-2010 3:35pm

unlikely that the heating being on has boiled the water into steam and evaporated... anyway that would probably only happen to the bottom of the coil so there should still be 4" of water in it or so.

dunno.. im stumpt

Tiercel Dave · 26-12-2010 3:51pm

Just had a quick look at this and can't figure it out yet but to put one more ingredient into the mix I've seen a cylinder where the coil inside was leaking into the domestic water. It's a hard one to spot cause the heating water and the domestic water are mixing but no water is being lost! Dave

sitja · 26-12-2010 4:54pm

ya its a mystery, was finding it hard to believe until i witnessed it.So basically while heating is on the cylinder just starts to deform, roughly after 20 minutes.

2 stroke · 27-12-2010 2:07am

Coil is burst inside cylinder, cylinder is sucked in when ch pump starts. Saw this before, realy baffling.

Buford T Justice · 27-12-2010 2:19am

2 stroke wrote: »

Coil is burst inside cylinder, cylinder is sucked in when ch pump starts. Saw this before, realy baffling.

How can this happen? If its a pressurized system, then the CH pressure will leak into the water until the pressure equalizes, and there will be no vacuum to draw the water out of the cylinder and cause the collapse. Plus, when water heats it would expand out of the coil, and not inwards.

Likewise with an open system, it will have the same head of pressure as the dhw system, and no way of creating a vacuum.

Definitely a strange one.

sitja · 27-12-2010 11:36am

its an open system, maybe he means when c.h is on the pump pulling the water through the coil is creating a negative pressure causing cylinder to collapse. It takes up to 20 or 30 minutes before it actually starts happening though?

Buford T Justice · 27-12-2010 1:25pm

sitja wrote: »

its an open system, maybe he means when c.h is on the pump pulling the water through the coil is creating a negative pressure causing cylinder to collapse. It takes up to 20 or 30 minutes before it actually starts happening though?

Don't think so. The CH pump will be able to bypass the coil in the cylinder anyway due to the way it'll be plumbed.

Plus, it would just collapse the coil in the cylinder, you would need a much greater vacuum to do it to the tank itself.

2 stroke · 27-12-2010 4:03pm

Fingers McGee wrote: »

How can this happen? If its a pressurized system, then the CH pressure will leak into the water until the pressure equalizes, and there will be no vacuum to draw the water out of the cylinder and cause the collapse. Plus, when water heats it would expand out of the coil, and not inwards.

Likewise with an open system, it will have the same head of pressure as the dhw system, and no way of creating a vacuum.

Definitely a strange one.

My earlier post was a drunken one, this is a hungover one.

It can happen in an open system if feed and expansion pipes are blocked or frozen. cylinder can be sucked in when ch pump starts if coil is leaking inside cylinder.

sitja · 27-12-2010 7:08pm

Ya i assumed you meant that the cold feed an expansion were blocked and in a open system. Only thing i wonder though is.... i have seen the water in these rads and there not very clean, i know this is a sign of corrosion, but if it the coil was leaking wouldnt it also discolour the dhw in the cylinder and be obvious enough that something is not right when drawing water from the hot taps.

Buford T Justice · 27-12-2010 8:27pm

sitja wrote: »

Ya i assumed you meant that the cold feed an expansion were blocked and in a open system. Only thing i wonder though is.... i have seen the water in these rads and there not very clean, i know this is a sign of corrosion, but if it the coil was leaking wouldnt it also discolour the dhw in the cylinder and be obvious enough that something is not right when drawing water from the hot taps.

Yes it would. If the CH coil was leaking water out into the DHW then you'd know about it.

cylinder collapse.

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