Expansion vessel. Rookie mistake
 

Our mains pressure HW system has an external expansion vessel.

Lately its not being doing its job and water has been trickling through
the pressure relief valve whenever it was heating up.

I had tried unsuccessfully to recharge it with my bicycle track pump but I
ended up convincing myself that the internal rubber bag had failed.

Anyhow, took the bull by the horns today and depressurised the HW system
and undid the pipe connection. I then unscrewed the securing jubilee clips
that hold it to the wall bracket.

**** me but the holding it up with one hand in the top of the airing
cupboard and trying to lift it off the pipe work was not happening! Managed
to undo another pipe joint and to free the unit and then dragged it out of
the cupboard.

Turned out of course that it was still full of water and at about 30cm wide
and 40 cm tall it would hold around 28L!

With hindsight I should obviously have let air into the top of the tank to
allow it to drain. Wont make that mistake again!

The bag actually seemed fine and once reinstalled and re-pressurised to 3
bar there was no evidence of any leak.

Tim

--
Please don't feed the trolls

Expansion vessel. Rookie mistake
 

On 07/04/2021 18:07, Tim+ wrote:
Our mains pressure HW system has an external expansion vessel.

Lately its not being doing its job and water has been trickling through
the pressure relief valve whenever it was heating up.

I had tried unsuccessfully to recharge it with my bicycle track pump but I
ended up convincing myself that the internal rubber bag had failed.

Anyhow, took the bull by the horns today and depressurised the HW system
and undid the pipe connection. I then unscrewed the securing jubilee clips
that hold it to the wall bracket.

**** me but the holding it up with one hand in the top of the airing
cupboard and trying to lift it off the pipe work was not happening! Managed
to undo another pipe joint and to free the unit and then dragged it out of
the cupboard.

Turned out of course that it was still full of water and at about 30cm wide
and 40 cm tall it would hold around 28L!

With hindsight I should obviously have let air into the top of the tank to
allow it to drain. Wont make that mistake again!

The bag actually seemed fine and once reinstalled and re-pressurised to 3
bar there was no evidence of any leak.

Tim

Thanks for owning-up; it might save me from making the same mistake when
the day (inevitably) arrives.

Expansion vessel. Rookie mistake
 

On 07/04/2021 18:07, Tim+ wrote:
Our mains pressure HW system has an external expansion vessel.

Lately its not being doing its job and water has been trickling through
the pressure relief valve whenever it was heating up.

I had tried unsuccessfully to recharge it with my bicycle track pump but I
ended up convincing myself that the internal rubber bag had failed.

Anyhow, took the bull by the horns today and depressurised the HW system
and undid the pipe connection. I then unscrewed the securing jubilee clips
that hold it to the wall bracket.

**** me but the holding it up with one hand in the top of the airing
cupboard and trying to lift it off the pipe work was not happening! Managed
to undo another pipe joint and to free the unit and then dragged it out of
the cupboard.

Turned out of course that it was still full of water and at about 30cm wide
and 40 cm tall it would hold around 28L!

With hindsight I should obviously have let air into the top of the tank to
allow it to drain. Wont make that mistake again!

The bag actually seemed fine and once reinstalled and re-pressurised to 3
bar there was no evidence of any leak.

Tim

With the bag failed you would get water out of the shraeder valve,
especially if you remove the insert completely.

Remember that for repressurising, you should really have the hot water
circuit completely depressurised so that the diaphragm can force all the
water out back into the system. To save that faff, on my system I have
an isolating valve to the hot water circuit and a drain valve for the
vessel itself. Obviously, you need to remember to open the isolating
valve once you have repressurised the vessel (and really you should do
that when the heating is off).

Expansion vessel. Rookie mistake
 

On 7 Apr 2021 at 18:47:18 BST, "newshound"
wrote:

On 07/04/2021 18:07, Tim+ wrote:
Our mains pressure HW system has an external expansion vessel.

Lately its not being doing its job and water has been trickling through
the pressure relief valve whenever it was heating up.

I had tried unsuccessfully to recharge it with my bicycle track pump but I
ended up convincing myself that the internal rubber bag had failed.

Anyhow, took the bull by the horns today and depressurised the HW system
and undid the pipe connection. I then unscrewed the securing jubilee clips
that hold it to the wall bracket.

**** me but the holding it up with one hand in the top of the airing
cupboard and trying to lift it off the pipe work was not happening! Managed
to undo another pipe joint and to free the unit and then dragged it out of
the cupboard.

Turned out of course that it was still full of water and at about 30cm wide
and 40 cm tall it would hold around 28L!

With hindsight I should obviously have let air into the top of the tank to
allow it to drain. Wont make that mistake again!

The bag actually seemed fine and once reinstalled and re-pressurised to 3
bar there was no evidence of any leak.

Tim

With the bag failed you would get water out of the shraeder valve,
especially if you remove the insert completely.

Remember that for repressurising, you should really have the hot water
circuit completely depressurised so that the diaphragm can force all the
water out back into the system. To save that faff, on my system I have
an isolating valve to the hot water circuit and a drain valve for the
vessel itself. Obviously, you need to remember to open the isolating
valve once you have repressurised the vessel (and really you should do
that when the heating is off).

Otherwise you would need to pressurise it up to about 4 bar or more which
would be possible but difficult with a bicycle pump.

--
Roger Hayter

Expansion vessel. Rookie mistake
 

Roger Hayter wrote:
On 7 Apr 2021 at 18:47:18 BST, "newshound"
wrote:

On 07/04/2021 18:07, Tim+ wrote:
Our mains pressure HW system has an external expansion vessel.

Lately its not being doing its job and water has been trickling through
the pressure relief valve whenever it was heating up.

I had tried unsuccessfully to recharge it with my bicycle track pump but I
ended up convincing myself that the internal rubber bag had failed.

Anyhow, took the bull by the horns today and depressurised the HW system
and undid the pipe connection. I then unscrewed the securing jubilee clips
that hold it to the wall bracket.

**** me but the holding it up with one hand in the top of the airing
cupboard and trying to lift it off the pipe work was not happening! Managed
to undo another pipe joint and to free the unit and then dragged it out of
the cupboard.

Turned out of course that it was still full of water and at about 30cm wide
and 40 cm tall it would hold around 28L!

With hindsight I should obviously have let air into the top of the tank to
allow it to drain. Wont make that mistake again!

The bag actually seemed fine and once reinstalled and re-pressurised to 3
bar there was no evidence of any leak.

Tim

With the bag failed you would get water out of the shraeder valve,
especially if you remove the insert completely.

Remember that for repressurising, you should really have the hot water
circuit completely depressurised so that the diaphragm can force all the
water out back into the system. To save that faff, on my system I have
an isolating valve to the hot water circuit and a drain valve for the
vessel itself. Obviously, you need to remember to open the isolating
valve once you have repressurised the vessel (and really you should do
that when the heating is off).

Otherwise you would need to pressurise it up to about 4 bar or more which
would be possible but difficult with a bicycle pump.


A track pump can do 100psi (7ish bar) with no difficulty. Problem is small
stroke volume compared to size of reservoir and trying to use it standing
on a stool in the top of the wiring cupboard! ;-)

Tim

--
Please don't feed the trolls

Expansion vessel. Rookie mistake
 

On 07/04/2021 22:01, Tim+ wrote:
Roger Hayter wrote:
On 7 Apr 2021 at 18:47:18 BST, "newshound"
wrote:

On 07/04/2021 18:07, Tim+ wrote:
Our mains pressure HW system has an external expansion vessel.

Lately its not being doing its job and water has been trickling through
the pressure relief valve whenever it was heating up.

I had tried unsuccessfully to recharge it with my bicycle track pump but I
ended up convincing myself that the internal rubber bag had failed.

Anyhow, took the bull by the horns today and depressurised the HW system
and undid the pipe connection. I then unscrewed the securing jubilee clips
that hold it to the wall bracket.

**** me but the holding it up with one hand in the top of the airing
cupboard and trying to lift it off the pipe work was not happening! Managed
to undo another pipe joint and to free the unit and then dragged it out of
the cupboard.

Turned out of course that it was still full of water and at about 30cm wide
and 40 cm tall it would hold around 28L!

With hindsight I should obviously have let air into the top of the tank to
allow it to drain. Wont make that mistake again!

The bag actually seemed fine and once reinstalled and re-pressurised to 3
bar there was no evidence of any leak.

Tim

With the bag failed you would get water out of the shraeder valve,
especially if you remove the insert completely.

Remember that for repressurising, you should really have the hot water
circuit completely depressurised so that the diaphragm can force all the
water out back into the system. To save that faff, on my system I have
an isolating valve to the hot water circuit and a drain valve for the
vessel itself. Obviously, you need to remember to open the isolating
valve once you have repressurised the vessel (and really you should do
that when the heating is off).

Otherwise you would need to pressurise it up to about 4 bar or more which
would be possible but difficult with a bicycle pump.


A track pump can do 100psi (7ish bar) with no difficulty. Problem is small
stroke volume compared to size of reservoir and trying to use it standing
on a stool in the top of the wiring cupboard! ;-)

Tim

Not if you have one of the little Lidl tyre pumps running of their 20v
lithium batteries! (Actually I have not checked what pressure it gets up
to, but it was very handy the other day using the football filler
"hypodermic" to blow out the jets of the carb on my two stroke hedge
trimmer). It does have quite a reasonable volumetric flow, certainly
enough for an expansion vessel.

Expansion vessel. Rookie mistake
 

On 07/04/2021 18:07, Tim+ wrote:
Our mains pressure HW system has an external expansion vessel.

Lately its not being doing its job and water has been trickling through
the pressure relief valve whenever it was heating up.

I had tried unsuccessfully to recharge it with my bicycle track pump but I
ended up convincing myself that the internal rubber bag had failed.

Anyhow, took the bull by the horns today and depressurised the HW system
and undid the pipe connection. I then unscrewed the securing jubilee clips
that hold it to the wall bracket.

**** me but the holding it up with one hand in the top of the airing
cupboard and trying to lift it off the pipe work was not happening! Managed
to undo another pipe joint and to free the unit and then dragged it out of
the cupboard.

Turned out of course that it was still full of water and at about 30cm wide
and 40 cm tall it would hold around 28L!

With hindsight I should obviously have let air into the top of the tank to
allow it to drain. Wont make that mistake again!

The bag actually seemed fine and once reinstalled and re-pressurised to 3
bar there was no evidence of any leak.

The normal procedure for checking and re-pressurising is to:

Turn off mains cold inlet to cylinder.
Open a hot tap somewhere - water will drain until any water in the
expansion vessel is expelled.

Now check the pressure at the shrader valve. If it's less than
(typically) 3 bar, add air until it's at 3 bar.

Close the hot tap, and open the inlet valve to the cylinder.

I added some notes to the maintenance section:

http://wiki.diyfaq.org.uk/index.php/...g_requirements


--
Cheers,

John.

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

Expansion vessel. Rookie mistake
 

newshound wrote:
On 07/04/2021 22:01, Tim+ wrote:


A track pump can do 100psi (7ish bar) with no difficulty. Problem is small
stroke volume compared to size of reservoir and trying to use it standing
on a stool in the top of the wiring cupboard! ;-)

Tim

Not if you have one of the little Lidl tyre pumps running of their 20v
lithium batteries! (Actually I have not checked what pressure it gets up
to, but it was very handy the other day using the football filler
"hypodermic" to blow out the jets of the carb on my two stroke hedge
trimmer). It does have quite a reasonable volumetric flow, certainly
enough for an expansion vessel.

Certainly would have been nice to have! Must look out for one.

Tim



--
Please don't feed the trolls

Expansion vessel. Rookie mistake
 

On 07/04/2021 22:01, Tim+ wrote:
Roger Hayter wrote:
On 7 Apr 2021 at 18:47:18 BST, "newshound"
wrote:

On 07/04/2021 18:07, Tim+ wrote:
Our mains pressure HW system has an external expansion vessel.

Lately its not being doing its job and water has been trickling through
the pressure relief valve whenever it was heating up.

I had tried unsuccessfully to recharge it with my bicycle track pump but I
ended up convincing myself that the internal rubber bag had failed.

Anyhow, took the bull by the horns today and depressurised the HW system
and undid the pipe connection. I then unscrewed the securing jubilee clips
that hold it to the wall bracket.

**** me but the holding it up with one hand in the top of the airing
cupboard and trying to lift it off the pipe work was not happening! Managed
to undo another pipe joint and to free the unit and then dragged it out of
the cupboard.

Turned out of course that it was still full of water and at about 30cm wide
and 40 cm tall it would hold around 28L!

With hindsight I should obviously have let air into the top of the tank to
allow it to drain. Wont make that mistake again!

The bag actually seemed fine and once reinstalled and re-pressurised to 3
bar there was no evidence of any leak.

Tim

With the bag failed you would get water out of the shraeder valve,
especially if you remove the insert completely.

Remember that for repressurising, you should really have the hot water
circuit completely depressurised so that the diaphragm can force all the
water out back into the system. To save that faff, on my system I have
an isolating valve to the hot water circuit and a drain valve for the
vessel itself. Obviously, you need to remember to open the isolating
valve once you have repressurised the vessel (and really you should do
that when the heating is off).

Otherwise you would need to pressurise it up to about 4 bar or more which
would be possible but difficult with a bicycle pump.


A track pump can do 100psi (7ish bar) with no difficulty. Problem is small
stroke volume compared to size of reservoir and trying to use it standing
on a stool in the top of the wiring cupboard! ;-)

Tim


a hobby mains powered compressor with an air hose and a tyre inflator
guage makes this easy.....

Expansion vessel. Rookie mistake
 

On 07/04/2021 23:37, John Rumm wrote:
On 07/04/2021 18:07, Tim+ wrote:
Our mains pressure HW system has an external expansion vessel.

Lately its not being doing its job and water has been trickling through
the pressure relief valve whenever it was heating up.

I had tried unsuccessfully to recharge it with my bicycle track pump
but I
ended up convincing myself that the internal rubber bag had failed.

Anyhow, took the bull by the horns today and depressurised the HW system
and undid the pipe connection.Â* I then unscrewed the securing jubilee
clips
that hold it to the wall bracket.

**** me but the holding it up with one hand in the top of the airing
cupboard and trying to lift it off the pipe work was not happening!
Managed
to undo another pipe joint and to free the unit and then dragged it
out of
the cupboard.

Turned out of course that it was still full of water and at about 30cm
wide
and 40 cm tall it would hold around 28L!

With hindsight I should obviously have let air into the top of the
tank to
allow it to drain. Wont make that mistake again!

The bag actually seemed fine and once reinstalled and re-pressurised to 3
bar there was no evidence of any leak.

The normal procedure for checking and re-pressurising is to:

Turn off mains cold inlet to cylinder.
Open a hot tap somewhere - water will drain until any water in the
expansion vessel is expelled.

Now check the pressure at the shrader valve. If it's less than
(typically) 3 bar, add air until it's at 3 bar.

Close the hot tap, and open the inlet valve to the cylinder.

I added some notes to the maintenance section:

http://wiki.diyfaq.org.uk/index.php/...g_requirements


Only for unvented DHW though. For combis, or "system" boiler with vented
DHW you need "my" method. I must admit I had not noticed when I posted
earlier that Tim has unvented DHW.

Expansion vessel. Rookie mistake
 

On 23:37 7 Apr 2021, John Rumm said:
On 07/04/2021 18:07, Tim+ wrote:


Our mains pressure HW system has an external expansion vessel.

Lately it's not being doing its job and water has been trickling
through the pressure relief valve whenever it was heating up.

I had tried unsuccessfully to recharge it with my bicycle track
pump but I ended up convincing myself that the internal rubber
bag had failed.

Anyhow, took the bull by the horns today and depressurised the HW
system and undid the pipe connection. I then unscrewed the
securing jubilee clips that hold it to the wall bracket.

**** me but the holding it up with one hand in the top of the
airing cupboard and trying to lift it off the pipe work was not
happening! Managed to undo another pipe joint and to free the
unit and then dragged it out of the cupboard.

Turned out of course that it was still full of water and at about
30cm wide and 40 cm tall it would hold around 28L!

With hindsight I should obviously have let air into the top of
the tank to allow it to drain. Won't make that mistake again!

The bag actually seemed fine and once reinstalled and
re-pressurised to 3 bar there was no evidence of any leak.

The normal procedure for checking and re-pressurising is to:

Turn off mains cold inlet to cylinder. Open a hot tap somewhere -
water will drain until any water in the expansion vessel is
expelled.

Now check the pressure at the shrader valve. If it's less than
(typically) 3 bar, add air until it's at 3 bar.

Close the hot tap, and open the inlet valve to the cylinder.

I added some notes to the maintenance section:

http://wiki.diyfaq.org.uk/index.php/...DHW#Servicing_
requirements

This reminds me ... not long ago I was asking here about a failing
expansion vessel inside my boiler.

http://al.howardknight.net/?ID=161797506000

I had a new one fitted in the external pipework. Should the failed
expansion vessel inside the boiler have been isolated or perhaps
drained?

Expansion vessel. Rookie mistake
 

Pamela wrote:


I had a new one fitted in the external pipework. Should the failed
expansion vessel inside the boiler have been isolated or perhaps
drained?


I cant see that it would be worth the bother. Presumably you had an
external one fitted because changing the internal one was bothersome.

Tim


--
Please don't feed the trolls

Expansion vessel. Rookie mistake
 

On 18:57 9 Apr 2021, Tim+ said:

Pamela wrote:


I had a new one fitted in the external pipework. Should the
failed expansion vessel inside the boiler have been isolated or
perhaps drained?


I can't see that it would be worth the bother. Presumably you
had an external one fitted because changing the internal one was
bothersome.

Tim

That's correct: it was filling and emptying in an erratic way. It's
still in series with the new expansion tank in the water circuit.

Expansion vessel. Rookie mistake
 

On Wednesday, 7 April 2021 at 23:37:35 UTC+1, John Rumm wrote:
..
Now check the pressure at the shrader valve. If it's less than
(typically) 3 bar, add air until it's at 3 bar.

For what it's worth I note that the instructions for my vessel say to pump it up to 0.2 bar less than the static pressure. I've always assumed it is to give a slight positive bias in the direction of intended travel so as to minimise stresses when it returns to the at-rest position.

Expansion vessel. Rookie mistake
 

On 10/04/2021 14:23, Mathew Newton wrote:
On Wednesday, 7 April 2021 at 23:37:35 UTC+1, John Rumm wrote: .
Now check the pressure at the shrader valve. If it's less than
(typically) 3 bar, add air until it's at 3 bar.

For what it's worth I note that the instructions for my vessel say to
pump it up to 0.2 bar less than the static pressure. I've always
assumed it is to give a slight positive bias in the direction of
intended travel so as to minimise stresses when it returns to the
at-rest position.

It depends a bit on what the PRV on the inlet is set to (and the water
pressure if its less than the PRV setting)

--
Cheers,

John.

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

Expansion vessel. Rookie mistake
 

On Sunday, 11 April 2021 at 00:15:32 UTC+1, John Rumm wrote:

For what it's worth I note that the instructions for my vessel say to
pump it up to 0.2 bar less than the static pressure. I've always
assumed it is to give a slight positive bias in the direction of
intended travel so as to minimise stresses when it returns to the
at-rest position.
It depends a bit on what the PRV on the inlet is set to (and the water
pressure if its less than the PRV setting)

Yes, I'd take the lower of the two as the reference.