expansion vessel

Wearb · 05-03-2014 8:02pm #1

Would this work?
I want to check pressure in a vessel and don't want to drain down the system. The vessel is downstairs and the bleed screw of the highest radiator is 3 metres (head) above it.
If I turn off the mains water supply and leave the top radiator screw open (collecting excess water), I think I can accurately pressurise the vessel.
This head of water will create about .3 bar at the vessel. Supposing that the vessel required 1 bar, then in this case if I put .7 bar in the vessel, would it amount to the same thing?
Am I missing something here? Why is it not done this way?

Dtp1979 · 05-03-2014 8:22pm

Wearb wrote: »

Would this work?
I want to check pressure in a vessel and don't want to drain down the system. The vessel is downstairs and the bleed screw of the highest radiator is 3 metres (head) above it.
If I turn off the mains water supply and leave the top radiator screw open (collecting excess water), I think I can accurately pressurise the vessel.
This head of water will create about .3 bar at the vessel. Supposing that the vessel required 1 bar, then in this case if I put .7 bar in the vessel, would it amount to the same thing?
Am I missing something here? Why is it not done this way?

I dunno wearb. I know someone that used to be here that'd know

scudo2 · 05-03-2014 8:24pm

It will work no problem there.
You will have quite a bit of water though.

Make sure no pumps are on !!
I do similar with oil boiler drain cocks, drop the water pressure to 0. leave it open a small bit, top up pressure vessel, while water pressure stayes between 0-0.1
Check air valve for leakage then top up water = no air locked.

Doom · 05-03-2014 8:25pm

Are the expansion vessels not pre-charged?

scudo2 · 05-03-2014 8:43pm

Doom wrote: »

Are the expansion vessels not pre-charged?

Ment to be !!!
But you should always check with a small pen type pressure gauge, + manufactures recommend that you do, just to cover you and themselves.

I was in boiler manufactures last year, a manager and myself checked them out of cueriousty, 20% had only .5 bar

They should ALWAYS be checked at a service. Handy if they have a flexy hose, you can just lift them to feel if they have water in them before pumping them up.

05-03-2014 8:53pm

If I check a vessel I take all the pressure off the otherside of the membrane, i am happy to do so because i'v been caught out before and I don't trust anything else.

Egass13 · 05-03-2014 9:01pm

gary71 wrote: »

If I check a vessel I take all the pressure off the otherside of the membrane, i am happy to do so because i'v been caught out before and I don't trust anything else.

I would be of the same opinon, prefer to have them empty just to guarantee the pressure is correct

scudo2 · 05-03-2014 9:14pm

gary71 wrote: »

If I check a vessel I take all the pressure off the otherside of the membrane, i am happy to do so because i'v been caught out before and I don't trust anything else.

I ment a tiny bit of water, less than a half cup full, or empty + water pressure is also at 0 when I get there, so I know there is no need to drain before pumping.
If its half full and you pump without draining then only filling 70% of the vessel.
But you and I + most others already know that.

05-03-2014 9:30pm

scudo2 wrote: »

I ment a tiny bit of water, less than a half cup full, or empty + water pressure is also at 0 when I get there, so I know there is no need to drain before pumping.
If its half full and you pump without draining then only filling 70% of the vessel.
But you and I + most others already know that.

Gas boiler expansion vessels are a bit different they are susceptible to blockage between the vessel and the boiler so I fully drain the boiler to prove the boiler isn't making a fool of me, which it has in the past.

corkgsxr · 05-03-2014 9:45pm

Your just guessing at pressure that way. Id only do it with no pressure at the other side.

Egass13 · 05-03-2014 10:00pm

gary71 wrote: »

Gas boiler expansion vessels are a bit different they are susceptible to blockage between the vessel and the boiler so I fully drain the boiler to prove the boiler isn't making a fool of me, which it gas in the past.

Happened to me on a mynute 16e , flexi hose blocked solid . Of course I fitted a new vessel before I coped it but we learn from our mistakes I suppose

Wearb · 05-03-2014 10:02pm

corkgsxr wrote: »

Your just guessing at pressure that way. Id only do it with no pressure at the other side.

I don't think it's guesswork the way I described it. A certain colum of water excerts a certain pressure.

Wearb · 05-03-2014 10:05pm

Doom wrote: »

Are the expansion vessels not pre-charged?

They can be, but they still need to be checked. As Scudo said.

05-03-2014 10:09pm

Doom wrote: »

Are the expansion vessels not pre-charged?

I don't trust nuffink

scudo2 · 05-03-2014 10:15pm

gary71 wrote: »

Gas boiler expansion vessels are a bit different they are susceptible to blockage between the vessel and the boiler so I fully drain the boiler to prove the boiler isn't making a fool of me, which it has in the past.

Good point. Thanks

I'm getting older and wiser every day.

Wearb · 05-03-2014 10:15pm

Egass13 wrote: »

I would be of the same opinon, prefer to have them empty just to guarantee the pressure is correct

Does that mean draining down the system.

Would a way to check for blockage like this work; check vessel pressure and water pressure, put a little extra pressure in vessel and watch for increase in water pressure and then put vessel back to original pressure?
Lack of increase in water pressure would indicate blockage.

scudo2 · 05-03-2014 10:18pm

Wearb wrote: »

Does that mean draining down the system.

Would a way to check for blockage like this work; check vessel pressure and water pressure, put a little extra pressure in vessel and watch for increase in water pressure and then put vessel back to original pressure?
Lack of increase in water pressure would indicate blockage.

Only if there's water in the pressure vessel to shove back into the heating system.

No need to totaly drain system, just drop pressure to 0

05-03-2014 10:21pm

Wearb wrote: »

Does that mean draining down the system.

Would a way to check for blockage like this work; check vessel pressure and water pressure, put a little extra pressure in vessel and watch for increase in water pressure and then put vessel back to original pressure?
Lack of increase in water pressure would indicate blockage.

When working on a gas boiler I'm ticking boxs, to not do this can lead to doubts in my mind, also i'v missed faults and chased my own tail by not following my own boring process of elimination.

Wearb · 05-03-2014 10:32pm

scudo2 wrote: »

Only if there's water in the pressure vessel to shove back into the heating system.

No need to totaly drain system, just drop pressure to 0

Agree about vessel (your first paragraph), perhaps increase water pressure and watch for rise in vessel pressure.

Would be impossible to drop down to zero in the case I described, because the water upstairs would be exerting pressure unless drained down to vessel level.

Wearb · 05-03-2014 10:37pm

gary71 wrote: »

When working on a gas boiler I'm ticking boxs, to not do this can lead to doubts in my mind, also i'v missed faults and chased my own tail by not following my own boring process of elimination.

Yes that I totally understand. I have arrived at faults with preconceived ideas that delayed my fix, instead of following well tried and tested diagnostic procedures.

scudo2 · 05-03-2014 10:39pm

Wearb wrote: »

Agree about vessel (your first paragraph), perhaps increase water pressure and watch for rise in vessel pressure.

Would be impossible to drop down to zero in the case I described, because the water upstairs would be exerting pressure unless drained down to vessel level.

Almost 0
A sealed system will not produce or excert pressure from upstairs as it will form a vacume, unless there is an auto air vent in the hotpress to allow air back in breaking vacume effect.

Wearb · 05-03-2014 10:46pm

scudo2 wrote: »

Almost 0
A sealed system will not produce or excert pressure from upstairs as it will form a vacume, unless there is an auto air vent in the hotpress to allow air back in breaking vacume effect.

Thanks Scudo. Would the vacuum not try to get air through the drain point, like the way turning a bottle upside down does?

scudo2 · 05-03-2014 11:02pm

Wearb wrote: »

Thanks Scudo. Would the vacuum not try to get air through the drain point, like the way turning a bottle upside down does?

Not if the hose is attatched. Or the valve is only open a small bit.
If air can't get in water can't escape.

With a vacume, water and atmospheric air pressure are equil at drain cock.

Wearb · 05-03-2014 11:10pm

scudo2 wrote: »

Not if the hose is attatched. Or the valve is only open a small bit.
If air can't get in water can't escape.

With a vacume, water and atmospheric air pressure are equil at drain cock.

Thanks. I Will try it next time.

K.Flyer · 06-03-2014 12:51am

Wearb wrote: »

Would this work?
I want to check pressure in a vessel and don't want to drain down the system. The vessel is downstairs and the bleed screw of the highest radiator is 3 metres (head) above it.
If I turn off the mains water supply and leave the top radiator screw open (collecting excess water), I think I can accurately pressurise the vessel.
This head of water will create about .3 bar at the vessel. Supposing that the vessel required 1 bar, then in this case if I put .7 bar in the vessel, would it amount to the same thing?
Am I missing something here? Why is it not done this way?

In this situation and after neutralising the pressure, I would go to the hot press and take off the auto vent. Then connect a hose (with a hose clip) long enough to run down stairs and outside, ensure DHW circuit is fully open and pump away.
My reasoning being that you cannot tell how much water is in a vessel before you start pumping. So by doing this any water volume displaced from the vessel is free to leave the system safely and with little to no restriction.
Also, my understanding is if the pre-charge pressure for the vessel is say 1 bar, then this is the pressure as if the vessel was in your hands and not connected to anything. So with this in mind, in theory, if you have the vessel disconnected and pre-charge to 1 bar, then reconnect it to a .3 bar head then the pressure on the air valve should read 1.3bar. So to allow for head of pressure in your calculation I would think you add the .3 bar, meaning you are pumping up to 1.3 bar. (I am open to being corrected)

scudo2 · 06-03-2014 1:02am

K.Flyer wrote: »

In this situation and after neutralising the pressure, I would go to the hot press and take off the auto vent. Then connect a hose (with a hose clip) long enough to run down stairs and outside, ensure DHW circuit is fully open and pump away.
My reasoning being that you cannot tell how much water is in a vessel before you start pumping. So by doing this any water volume displaced from the vessel is free to leave the system safely and with little to no restriction.
Also, my understanding is if the pre-charge pressure for the vessel is say 1 bar, then this is the pressure as if the vessel was in your hands and not connected to anything. So with this in mind, in theory, if you have the vessel disconnected and pre-charge to 1 bar, then reconnect it to a .3 bar head then the pressure on the air valve should read 1.3bar. So to allow for head of pressure in your calculation I would think you add the .3 bar, meaning you are pumping up to 1.3 bar. (I am open to being corrected)

With all my wisdom a 8 ltr vessel can only hold 8 ltr water max.
As 12 ltr vessel can only hold 12 ltr water max !!
I'd throw in a few smile faces but haven't a clue how to with my phone.

Fair enough, you could pump out the whole system if diaphram is riped !!

I'm Trying to show the funny side rather than be sarcastic.

K.Flyer · 06-03-2014 1:33am

scudo2 wrote: »

With all my wisdom a 8 ltr vessel can only hold 8 ltr water max.
As 12 ltr vessel can only hold 12 ltr water max !!
I'd throw in a few smile faces but haven't a clue how to with my phone.

Fair enough, you could pump out the whole system if diaphram is riped !!

I'm Trying to show the funny side rather than be sarcastic.

No bother Mr.S

, my point was to show an easier way, rather than trying to pump out through a small orifice like a vent screw.

Wearb · 06-03-2014 10:38am

K.Flyer wrote: »

In this situation and after neutralising the pressure, I would go to the hot press and take off the auto vent. Then connect a hose (with a hose clip) long enough to run down stairs and outside, ensure DHW circuit is fully open and pump away.
My reasoning being that you cannot tell how much water is in a vessel before you start pumping. So by doing this any water volume displaced from the vessel is free to leave the system safely and with little to no restriction.
Also, my understanding is if the pre-charge pressure for the vessel is say 1 bar, then this is the pressure as if the vessel was in your hands and not connected to anything. So with this in mind, in theory, if you have the vessel disconnected and pre-charge to 1 bar, then reconnect it to a .3 bar head then the pressure on the air valve should read 1.3bar. So to allow for head of pressure in your calculation I would think you add the .3 bar, meaning you are pumping up to 1.3 bar. (I am open to being corrected)

I think that you are correct. I had the calculation the wrong way around.

Wearb · 06-03-2014 10:47am

scudo2 wrote: »

With all my wisdom a 8 ltr vessel can only hold 8 ltr water max.
As 12 ltr vessel can only hold 12 ltr water max !!
I'd throw in a few smile faces but haven't a clue how to with my phone.

Fair enough, you could pump out the whole system if diaphram is riped !!

I'm Trying to show the funny side rather than be sarcastic.

For smiley use a colon and a bracket like this. : ). I have put a space between my colon and bracket to stop it turning into a smiley for illustration purposes.

use other bracket for frown

murphaph · 06-03-2014 1:43pm

I'm a layman so go easy...

I have a question for the experts sort of related to this topic:
I have had to change a pump and an expansion vessel on my ancient gas boiler recently. I am not comfortable with partially draining the system as I always seem to get it airlocked when I refill-don't know why.

So anyway, I now drain the whole thing down (hose from rad below boiler, all rads on same floor (apartment) and all lower than boiler, flow and return pipes lead down from boiler into floor screed and round to the rads and back).

When I drain the whole thing down I open the drain cock and about 3 litres of water comes out and the manometer on the boiler hows 0 bar but of course as described upthread, there's a vacuum so no more water comes out until I remove the auto air vent at the very top of the boiler (on expansion vessel), then another litre or so comes out and it stops again until I crack the union to the expansion vessel and it carries on again for another litre or so and then it stops completely until I open the bleed screws on the rads (all of them) and then the system will finally drain (slowly) completely.

To refill system I leave everything open and slowly fill up until water comes out rad bleed screws, then I close them and fill up some more until it comes out the union under the expansion vessel then I tighten that ad then finally it comes out of the top of the expansion vessel and I replace the auto air release valve and then I fill up until I reach operating pressure.

My question is...why doesn't the whole system drain down when the vacuum is released at the boiler, can't the system suck air in there to empty the rads? (just curious...I hope I don't have to go near the thing again and if I do I'm going to replace it as it's 23 years old now)

scudo2 · 06-03-2014 4:05pm

Each rad. Boiler. Cylinder has a high point causing a vacume.
Air has to freely get in to allow water to drain out.

Dtp1979 · 06-03-2014 9:25pm

The thing that disturbs me there is a layman working on a 23 year old gas boiler

DGOBS · 06-03-2014 9:47pm

Agreed Declan, only RGI's are allowed to work on domestic gas appliances.

Please guys keep your gasworks questions & answers to the tech forum (as you always do)

murphaph · 06-03-2014 10:07pm

Dtp1979 wrote: »

The thing that disturbs me there is a layman working on a 23 year old gas boiler

A layman, but not an idiot. German law allows laymen to service the water circuit components of a gas boiler but prohibits interfering with any gas lines or control/ignition components. That's sensible enough IMO. It's different in Ireland, fair enough I'll leave it there.

Dtp1979 · 06-03-2014 10:18pm

murphaph wrote: »

A layman, but not an idiot. German law allows laymen to service the water circuit components of a gas boiler but prohibits interfering with any gas lines or control/ignition components. That's sensible enough IMO. It's different in Ireland, fair enough I'll leave it there.

My apologies I didn't realise it happened in Germany

scudo2 · 07-03-2014 9:10am

murphaph wrote: »

A layman, but not an idiot. German law allows laymen to service the water circuit components of a gas boiler but prohibits interfering with any gas lines or control/ignition components. That's sensible enough IMO. It's different in Ireland, fair enough I'll leave it there.

There is still a bit of confusion on the issue. I made 5 phone calls to experienced RGI's last night. Not board members, 4 out of 5 said its ok for non RGI to work on water end of boiler once cover wasn't removed. ie for external pump and pressure vessel work only, ( not internal )
1 said all water work was ok !!!

Nobody said
" no work anywhere near the boiler "

Billy Bunting · 07-03-2014 9:45am

I know several plumbers who work on GAS instantaneous water heaters, they say they don't break the gas supply, I passed this on to my RGII inspector and got a :rolleyes:

07-03-2014 10:50am

scudo2 wrote: »

There is still a bit of confusion on the issue. I made 5 phone calls to experienced RGI's last night. Not board members, 4 out of 5 said its ok for non RGI to work on water end of boiler once cover wasn't removed. ie for external pump and pressure vessel work only, ( not internal )
1 said all water work was ok !!!

Nobody said
" no work anywhere near the boiler "

Your talking about two different things, firstly gasworks ie anything on a gas appliance that requires the use of a tool secondly work outside of gasworks that may impact on a appliance ie... draining a heating system then refilling without bleeding the heat exchanger thus melting the boiler.

The second is not gas works but you would be in the gas do do as it were;)

murphaph · 07-03-2014 10:54am

scudo2 wrote: »

There is still a bit of confusion on the issue. I made 5 phone calls to experienced RGI's last night. Not board members, 4 out of 5 said its ok for non RGI to work on water end of boiler once cover wasn't removed. ie for external pump and pressure vessel work only, ( not internal )
1 said all water work was ok !!!

Nobody said
" no work anywhere near the boiler "

German boilers have lead seals on the bits you can't touch as a layman, but I bet the law is much clearer over here than in Ireland as to what is and is not allowed. If it's prohibited to even open the cover in Ireland then RGIs should carry one way seals that show if a boiler has been opened by a non RGI person or something. I personally think water work by a competent individual should be allowed inside the boiler casing, but that's a matter of opinion I suppose. I agree that under no circumstances should non-RGI folks mess with the gas stuff.

There are many things that can kill you in the family home. A poorly wired light fitting can easily be an electric shock hazard...but the law doesn't prohibit a home owner from putting up his own lights (I got a nice belt of such a light fitting in a house I own, luckily it didn't do any long term damage but it hurt like hell). In an apartment situation I can see some logic perhaps in an outright ban on laymen opening a gas boiler, but in your own house where you can't poison the neighbours, not so much (the law is full of contradictions of course...smoking kills people, yet it's not banned etc.)

Egass13 · 07-03-2014 11:22am

murphaph wrote: »

German boilers have lead seals on the bits you can't touch as a layman, but I bet the law is much clearer over here than in Ireland as to what is and is not allowed. If it's prohibited to even open the cover in Ireland then RGIs should carry one way seals that show if a boiler has been opened by a non RGI person or something. I personally think water work by a competent individual should be allowed inside the boiler casing, but that's a matter of opinion I suppose. I agree that under no circumstances should non-RGI folks mess with the gas stuff.

There are many things that can kill you in the family home. A poorly wired light fitting can easily be an electric shock hazard...but the law doesn't prohibit a home owner from putting up his own lights (I got a nice belt of such a light fitting in a house I own, luckily it didn't do any long term damage but it hurt like hell). In an apartment situation I can see some logic perhaps in an outright ban on laymen opening a gas boiler, but in your own house where you can't poison the neighbours, not so much (the law is full of contradictions of course...smoking kills people, yet it's not banned etc.)

Why is poisoning the neighbours considered worse than poisoning your own family? Every layman seems to have that view and to be honest it confuses me?

DGOBS · 07-03-2014 11:56am

Natural Gas and LPG are not poisonous! The explode, and that would affect your neighbours also!

Lets say, you take the cover off your boiler, and do some hydraulic work, change the pump etc, this could inadvertently cause a gas leak on the other fittings and components in the appliance in proximity to it during your works (have seen it more than once) and you would have neither the training or possibly the ability to test it correctly for safety.

Natural gas is lighter than air, so can easily move form one area (or property) to another, LPG is heavier than air and can pool in areas or find it's way into unsealed ducts, drains and basements. Unlike electricity, there is no 'RCD' there to protect you.

We have many German boilers installed and for sale in Ireland, I have not seen any with lead seals.

07-03-2014 1:05pm

DGOBS wrote: »

Natural Gas and LPG are not poisonous! The explode, and that would affect your neighbours also!

Lets say, you take the cover off your boiler, and do some hydraulic work, change the pump etc, this could inadvertently cause a gas leak on the other fittings and components in the appliance in proximity to it during your works (have seen it more than once) and you would have neither the training or possibly the ability to test it correctly for safety.

Natural gas is lighter than air, so can easily move form one area (or property) to another, LPG is heavier than air and can pool in areas or find it's way into unsealed ducts, drains and basements. Unlike electricity, there is no 'RCD' there to protect you.

We have many German boilers installed and for sale in Ireland, I have not seen any with lead seals.

Manufactures make boilers for specific country's regulations so a UK & Ireland boiler can very different from a boiler aimed at other EU country's.

DGOBS · 07-03-2014 2:35pm

I thought all gas appliance for sale in Europe comply with the Gas Appliance Directive?
Assume his must be due to regional requirements then?

murphaph · 07-03-2014 5:27pm

DGOBS wrote: »

I thought all gas appliance for sale in Europe comply with the Gas Appliance Directive?
Assume his must be due to regional requirements then?

The seals are not factory fitted AFAIK. I believe the "RGI"/Chimney sweep fit them upon commissioning the boiler and they are replaced by the "RGI" if he needs to work on affected components. It makes sense as the "RGI" guy will need to be able to remove the seals and replace them when he's working on the affected components.

gifted · 07-03-2014 6:38pm

scudo2 wrote: »

There is still a bit of confusion on the issue. I made 5 phone calls to experienced RGI's last night. Not board members, 4 out of 5 said its ok for non RGI to work on water end of boiler once cover wasn't removed. ie for external pump and pressure vessel work only, ( not internal )
1 said all water work was ok !!!

Nobody said
" no work anywhere near the boiler "

The whole system is seriously confused. In the last month I've removed a 6" gas header in work and replaced with a new 6" header with 3no 4" branches, all electric welded and gas welded. Piped a new 3" gas pipe up onto a roof, again all gas welded and will be connecting that into a CHP unit next week, but yet I'm not allowed work on a 1/2" copper pipe to a domestic boiler ( I have no interest in working on domestic boilers by the way).

IMO all gas pipework (domestic/commercial/industrial)should be covered with the same rules.
Replacement parts for gas boilers should only be sold to holders of RGII Id cards and the ID number of the RGI and serial number of the replacement part should be taken by the suppliers in case of any incidents, so the RGI can be traced by the serial number.

Thats my tuppence worth...sorry for boring ye.:o

murphaph · 07-03-2014 7:37pm

gifted wrote: »

The whole system is seriously confused. In the last month I've removed a 6" gas header in work and replaced with a new 6" header with 3no 4" branches, all electric welded and gas welded. Piped a new 3" gas pipe up onto a roof, again all gas welded and will be connecting that into a CHP unit next week, but yet I'm not allowed work on a 1/2" copper pipe to a domestic boiler ( I have no interest in working on domestic boilers by the way).

IMO all gas pipework (domestic/commercial/industrial)should be covered with the same rules.
Replacement parts for gas boilers should only be sold to holders of RGII Id cards and the ID number of the RGI and serial number of the replacement part should be taken by the suppliers in case of any incidents, so the RGI can be traced by the serial number.

Thats my tuppence worth...sorry for boring ye.:o

It's an interesting idea. It's a bit too big brother for me as someone who considers himself technically competent and happy to work on things. As I mentioned before...lots of things in the home have the capacity to kill you (including solid fuel stoves, electricity installations and so on) but we don't prohibit sale of light switches to the general public (wire a metal light switch wrong (live to earth contact) and you have a ready made death trap and not all properties have RCDs nor are required to have them!!!). Would you be happy if light switches were only sold to time served electricians? I know I wouldn't be. What about vehicles? I'm gonna change the front pads on my missus' car on Sunday...if I bugger it up I could kill her, my son and who knows who else. Should only time served mechanics be allowed to buy/replace brake pads? I'm sure most of the guys here are pretty handy and would be horrified at the idea of being prevented from working on their cars for H&S reasons.

gifted · 07-03-2014 8:44pm

murphaph wrote: »

It's an interesting idea. It's a bit too big brother for me as someone who considers himself technically competent and happy to work on things. As I mentioned before...lots of things in the home have the capacity to kill you (including solid fuel stoves, electricity installations and so on) but we don't prohibit sale of light switches to the general public (wire a metal light switch wrong (live to earth contact) and you have a ready made death trap and not all properties have RCDs nor are required to have them!!!). Would you be happy if light switches were only sold to time served electricians? I know I wouldn't be. What about vehicles? I'm gonna change the front pads on my missus' car on Sunday...if I bugger it up I could kill her, my son and who knows who else. Should only time served mechanics be allowed to buy/replace brake pads? I'm sure most of the guys here are pretty handy and would be horrified at the idea of being prevented from working on their cars for H&S reasons.

In my opinion they should be, I just paid €180 yesterday to get my family car serviced by a professional, I could have done it myself but why would I risk my family?
The point I was trying to make is that Domestic Gas works is covered by a law and it shouldn't be so easy for a non registered person to get spare parts.
Anyway, That's my own personal opinion, seeing as the above highlighted is not against the law then there's nothing stopping people from doing them

expansion vessel

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