I can't find any evidence that unvented cylinders require an annual
inspection.

T

wrote in message
...

I can't find any evidence that unvented cylinders require an annual
inspection.

Given their explosive potential in an overheat situation and a stuck
pressure relief valve, don't you sleep a little easier if it's been
inspected regularly? ;-)

It doesn't seem to be law but just prudent. http://yaph.co.uk/unvented/

Tim

On 2 Dec, 14:21, "Tim Downie"
wrote:
wrote in message

...



I can't find any evidence that unvented cylinders require an annual
inspection.

Given their explosive potential in an overheat situation and a stuck
pressure relief valve, don't you sleep a little easier if it's been
inspected regularly? ;-)

It doesn't seem to be law but just prudent. *http://yaph.co.uk/unvented/

Tim

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".

I became curious about this as it is supposedly one of the benefits of
a thermal store that annual certificated inspection isn't mandatory.
Yet another non-reason to get a thermal store!

T

wrote:
On 2 Dec, 14:21, "Tim Downie"
wrote:
wrote in message

...



I can't find any evidence that unvented cylinders require an annual
inspection.

Given their explosive potential in an overheat situation and a stuck
pressure relief valve, don't you sleep a little easier if it's been
inspected regularly? ;-)

It doesn't seem to be law but just prudent.
http://yaph.co.uk/unvented/

Tim

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.

As long as it's not going to affect others you can decide what level of risk
you're prepared to live with.

Tim

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. (after all, pressure testing of steam or
compressed air systems is often done with water because of its
significantly lower risk - its lack of compressibility making it very
difficult to store mechanical energy in it)

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 2 Dec, 15:10, John Rumm wrote:

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.

Not true. It's a pressurised system with an air reservoir. If
punctured, it will spray hot water at system pressure in a way that
vented systems won't. That's itself a hazard (depending on location).

Any central heating system capable of sinking a trawler (look it up!)
needs some degree of care in its maintenance.

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. (after all, pressure testing of steam or
compressed air systems is often done with water because of its
significantly lower risk - its lack of compressibility making it very
difficult to store mechanical energy in it)

But if it has an immersion element, then that would change the risks.

--
Rod

Hypothyroidism is a seriously debilitating condition with an insidious
onset.
Although common it frequently goes undiagnosed.
www.thyromind.info www.thyroiduk.org www.altsupportthyroid.org

On 2 Dec, 15:58, Andy Dingley wrote:
On 2 Dec, 15:10, John Rumm wrote:

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.

Not true. It's a pressurised system with an air reservoir. If
punctured, it will spray hot water at system pressure in a way that
vented systems won't. That's itself a hazard (depending on location).

Any central heating system capable of sinking a trawler (look it up!)
needs some degree of care in its maintenance.

The point, that annual certificated inspection of unvented hot water
tanks (at £50+ a pop) is not mandatory. I had been mislead into
thinking was is by people trying to sell me a thermal store. Being
lied to irritates me!

It is non sequitur to assume no checking or maintenance will be done.
I can assure you (never having had one of these things before) my
checking will be daily for quite some time after installation, even
knowing that there must be literally millions of the systems installed
safely across Europe, and that mine (with its internal expansion
chamber) is guaranteed for 25 years.

I will take your advice however, and refrain from attacking it with an
axe!

T

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.

Tim

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?
--
fred
BBC3, ITV2/3/4, channels going to the DOGs

On Tue, 2 Dec 2008 14:56:28 -0000
"Tim Downie" wrote:

wrote:
On 2 Dec, 14:21, "Tim Downie"
wrote:
wrote in message

...



I can't find any evidence that unvented cylinders require an annual
inspection.

Given their explosive potential in an overheat situation and a stuck
pressure relief valve, don't you sleep a little easier if it's been
inspected regularly? ;-)

It doesn't seem to be law but just prudent.
http://yaph.co.uk/unvented/

Tim

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.

As long as it's not going to affect others you can decide what level of risk
you're prepared to live with.

Tim



I have an OSO unvented cylinder (it's in the garage with the oil
boiler). I would like to check the safety valves myself, but where do
I find out how?

R.

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

Andy Dingley wrote:
On 2 Dec, 15:10, John Rumm wrote:

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.

Not true. It's a pressurised system with an air reservoir. If
punctured, it will spray hot water at system pressure in a way that
vented systems won't. That's itself a hazard (depending on location).

Agreed - hot water can come out in quantity and cause damage. It needs
careful thought applied to its location in the same way that any stored
hot water system does. After all, people have been killed by ordinary
hot water cylinders when they have ruptured (or deposited their content
into plastic cold water tanks) in lofts and deluged people asleep under
them.

However, that is not remotely similar to the explosive effect you see on
Dribble's oft posted link to a electrically heated sealed contained with
all the safety features defeated.

Any central heating system capable of sinking a trawler (look it up!)
needs some degree of care in its maintenance.

I don't know to which incident in particular you refer, but I would
presume if this was the result of an explosive blast from a water
heater, then it involved superheated water / steam.

There was a case where an American high rise apartment block was brought
down by a similar stored water system failure. (documented in the book
"Why buildings fall down" IIRC:

http://www.amazon.co.uk/exec/obidos/...ternodeltdcomp


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

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

--
Reentrant

Rod 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. (after all, pressure testing of steam
or compressed air systems is often done with water because of its
significantly lower risk - its lack of compressibility making it very
difficult to store mechanical energy in it)

But if it has an immersion element, then that would change the risks.

Yes it does - as would possibly a gravity circulated solid fuel stove.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

In article , Reentrant
writes

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

Oh god, tell me it's not the one where they had to weld it shut and
upgrade it to 10kW to get it to do what their agenda wanted it to?
--
fred
BBC3, ITV2/3/4, channels going to the DOGs

John Rumm wrote:
Andy Dingley wrote:
On 2 Dec, 15:10, John Rumm wrote:

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.

Not true. It's a pressurised system with an air reservoir. If
punctured, it will spray hot water at system pressure in a way that
vented systems won't. That's itself a hazard (depending on location).

Agreed - hot water can come out in quantity and cause damage. It needs
careful thought applied to its location in the same way that any
stored hot water system does. After all, people have been killed by
ordinary hot water cylinders when they have ruptured (or deposited
their content into plastic cold water tanks) in lofts and deluged
people asleep under them.

That's a good point that I'd fogotten about so that risk needs to be added
to the vented tank side of the equation. After all, if you've no loft tank
then that can't happen. I wonder how how many deaths have resulted from
this? Not a lot I'll wager but then probably not too many people have been
killed in the UK by unvented cylinders either.

Tim

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
Reply address works

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

On Tue, 02 Dec 2008 17:13:55 +0000, 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?
Don't forget

d) The manadatory backup over pressure device /over temperature device.



--
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

On Tue, 02 Dec 2008 17:26:25 +0000, John Rumm wrote:

Rod 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. (after all, pressure testing of steam
or compressed air systems is often done with water because of its
significantly lower risk - its lack of compressibility making it very
difficult to store mechanical energy in it)

But if it has an immersion element, then that would change the risks.

Yes it does - as would possibly a gravity circulated solid fuel stove.

Which are explicitly forbidden as a means of heating unvented HWCs.


--
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

On 2 Dec, 17:13, 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?
--
fred
BBC3, ITV2/3/4, channels going to the DOGs- Hide quoted text -

- Show quoted text -

You forgot the mandatory overtemperature relief valve!

On Tue, 02 Dec 2008 18:57:31 +0000, Kevin wrote:

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

Are George Goble's LOX-fuelled barbeque videos still around anywhere?!

--
John Stumbles

Press any key to continue or any other key to exit

In article
,
cynic writes
On 2 Dec, 17:13, 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?
--
fred
BBC3, ITV2/3/4, channels going to the DOGs- Hide quoted text -

- Show quoted text -

You forgot the mandatory overtemperature relief valve!

Ed just beat you to it :-)

I was thinking of pressure cooker type safety devices when I wrote that
and thought it was a potential weakness not to have a backup like the
melting plug that they have but it's nice to know they have it covered.
--
fred
BBC3, ITV2/3/4, channels going to the DOGs

"Ed Sirett" wrote in message
...


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

So to determine how safe it is you need to know the mean time between
failures of each device and the mean time to repair for the devices.
Then you can work out how long a system is likely to run without exploding.

dennis@home wrote:


"Ed Sirett" wrote in message
...


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

So to determine how safe it is you need to know the mean time between
failures of each device and the mean time to repair for the devices.
Then you can work out how long a system is likely to run without exploding.

depends on if they fail safe or not...


--
Cheers,

John.

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\================================================= ================/

"John Rumm" wrote in message
et...
dennis@home wrote:


"Ed Sirett" wrote in message
...


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

So to determine how safe it is you need to know the mean time between
failures of each device and the mean time to repair for the devices.
Then you can work out how long a system is likely to run without
exploding.

depends on if they fail safe or not...

I have yet to see a fail safe that can only fail safe.

wrote in message
...

I can't find any evidence that unvented cylinders require an annual
inspection.

Read the instructions.

wrote in message
...

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".

Have an explosion or leak and the insurance company will disown you.

wrote in message
...

The point, that annual certificated
inspection of unvented hot water
tanks (at £50+ a pop) is not mandatory.

It is. Read instructions.

I have the impression you are some sort of spammer.

"John Rumm" wrote in message
et...

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.

They all have electric immersions, which fail more easily.

"fred" wrote in message ...
In article , Reentrant
writes

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

Oh god, tell me it's not the one where they had to weld it shut and
upgrade it to 10kW to get it to do what their agenda wanted it to?

10kW was so they did not wait too long. It did go booooom.

"Ed Sirett" wrote in message
...

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

Quite possible on a very old neglected system. Expect many of this blows in
10, 20 years time as the install base rises.

Doctor Drivel wrote:
"fred" wrote in message ...
In article , Reentrant
writes

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

Oh god, tell me it's not the one where they had to weld it shut and
upgrade it to 10kW to get it to do what their agenda wanted it to?

10kW was so they did not wait too long. It did go booooom.

Very poor science then. Should have used a standard element and waited.
Heat loss by conduction *might* have been sufficient to prevent an explosion
but it'll require a repeat experiment to determine that.

Tim

Doctor Drivel wrote:

"John Rumm" wrote in message
et...

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.

You snipped the important bit however, which said "For a cylinder heated
via a water flow from a boiler, the chances of super heating it seem
minimal."

They all have electric immersions, which fail more easily.

Even if that were true (which I doubt), a large proportion are unlikely
to ever be heated via the immersion, given the added cost compared to
doing it with the boiler.

While immersion heaters obviously can fail, it would be interesting to
see how many (modern ones) fail in such a mode all the stats and
overheat protections fail, and yet they still carry on heating.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

"Tim Downie" wrote in message
...
Doctor Drivel wrote:
"fred" wrote in message ...
In article , Reentrant
writes

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

Oh god, tell me it's not the one where they had to weld it shut and
upgrade it to 10kW to get it to do what their agenda wanted it to?

10kW was so they did not wait too long. It did go booooom.

Very poor science then.

I am not interested in the science, it went boom. Big boom.

"John Rumm" wrote in message
et...

They all have electric immersions, which fail more easily.

Even if that were true

This is true.

(which I doubt), a large proportion are unlikely to ever be heated via the
immersion, given the added cost compared to doing it with the boiler.

A boom is a boom.

On 2 Dec, 19:05, Ed Sirett wrote:
On Tue, 02 Dec 2008 17:26:25 +0000, John Rumm wrote:
Rod 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. (after all, pressure testing of steam
or compressed air systems is often done with water because of its
significantly lower risk - its lack of compressibility making it very
difficult to store mechanical energy in it)

But if it has an immersion element, then that would change the risks.

Yes it does - as would possibly a gravity circulated solid fuel stove.

Which are explicitly forbidden as a means of heating unvented HWCs.

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

That's why you do it with a pump...

T

Doctor Drivel wrote:
"Tim Downie" wrote in message
...
Doctor Drivel wrote:
"fred" wrote in message ...
In article , Reentrant
writes

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

Oh god, tell me it's not the one where they had to weld it shut and
upgrade it to 10kW to get it to do what their agenda wanted it to?

10kW was so they did not wait too long. It did go booooom.

Very poor science then.

I am not interested in the science, it went boom. Big boom.

I think that says it all.

Tim

"Tim Downie" wrote in message
...
Doctor Drivel wrote:
"Tim Downie" wrote in message
...
Doctor Drivel wrote:
"fred" wrote in message ...
In article , Reentrant
writes

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

Oh god, tell me it's not the one where they had to weld it shut and
upgrade it to 10kW to get it to do what their agenda wanted it to?

10kW was so they did not wait too long. It did go booooom.

Very poor science then.

I am not interested in the science, it went boom. Big boom.

I think that says it all.

It said boom.