Issue with solid fuel stove connected to Systemlink

froshtyv · 30-12-2015 08:41PM #1

Hi,

Quick question,

I had an issue with the P&T valve on my cylinder blowing when the solid fuel stove has been lit.
If i am right, the stove should gravity feed to the coil in the cylinder and the pipe stat should then bring on the solid fuel pump which is feeding into one side of the system link and at the same time bring on a dump pump either GF rads or FF rads or both.
But at the moment the pressure / temperature is building in the cylinder until the P&T valve is activated.

Should this happen at all? I thought that the overflow tank in the attic would act as expansion for the solid fuel? For instance if there was a power cut when the solid fuel had been lit no pump could be brought on to act as a dump thus the hot water would expand up the pipes into the overflow?

Any suggestions or tips on the issue would be great thanks.

kerryplumber · 31-12-2015 02:23AM

froshtyv wrote: »

Hi,

Quick question,

I had an issue with the P&T valve on my cylinder blowing when the solid fuel stove has been lit.
If i am right, the stove should gravity feed to the coil in the cylinder and the pipe stat should then bring on the solid fuel pump which is feeding into one side of the system link and at the same time bring on a dump pump either GF rads or FF rads or both.
But at the moment the pressure / temperature is building in the cylinder until the P&T valve is activated.

Should this happen at all? I thought that the overflow tank in the attic would act as expansion for the solid fuel? For instance if there was a power cut when the solid fuel had been lit no pump could be brought on to act as a dump thus the hot water would expand up the pipes into the overflow?

Any suggestions or tips on the issue would be great thanks.

If the p&t valve is blowing off, I am assuming that u have a solid fuel stove plumbed into a pressurised cylinder???

roy rodgers · 31-12-2015 02:25AM

kerryplumber wrote: »

If the p&t valve is blowing off, I am assuming that u have a solid fuel stove plumbed into a pressurised cylinder???

Which should be a no no...

Dtp1979 · 31-12-2015 10:44AM

+1

kerryplumber · 31-12-2015 07:32PM

A definite no no!!!!!! But it does sound like that's the case here.

Dtp1979 · 31-12-2015 08:18PM

kerryplumber wrote: »

A definite no no!!!!!! But it does sound like that's the case here.

It must be. Never seen a t and p valve on an open vented cylinder

Dardania · 01-01-2016 12:37AM

Dtp1979 wrote: »

It must be. Never seen a t and p valve on an open vented cylinder

Not necessarily. There could be a valve between the cylinder and the overflow tank, which is closed, leading to the p and t blowing...

Dtp1979 · 01-01-2016 12:43AM

Dardania wrote: »

Not necessarily. There could be a valve between the cylinder and the overflow tank, which is closed, leading to the p and t blowing...

Yes but there is no reason to have a t&p valve on an open vented cylinder.

01-01-2016 01:40AM

Dtp1979 wrote: »

Yes but there is no reason to have a t&p valve on an open vented cylinder.

But that doesn't stop some installers from fitting them and I find there fitted often enough.

The installation should be checked by a decent plumber and I'd advise not using the stove until the installation has been checked for safety.

Dtp1979 · 01-01-2016 10:46AM

gary71 wrote: »

But that doesn't stop some installers from fitting them and I find there fitted often enough.

The installation should be checked by a decent plumber and I'd advise not using the stove until the installation has been checked for safety.

Me personally, I've never seen them fitted to an open vented cylinder. There's no harm in fitting one, but also no reason to either

my3cents · 01-01-2016 11:01AM

Where does the water go when one of these valves opens?

roy rodgers · 01-01-2016 11:03AM

If a t+p valve is fitted on a open vented system it shouldn't open as the excess heat and pressure should go up the expansion pipe I'd imagine

01-01-2016 12:15PM

Dtp1979 wrote: »

Me personally, I've never seen them fitted to an open vented cylinder. There's no harm in fitting one, but also no reason to either

I got caught out after I told a installer he had to pipe the T&P outlet in a safe manor, he told me he didn't as it was a open vented system and I should get my facts right before I say anythiny, so now I never assum

I think the reason there fitted is due to some unvented cylinders coming with the valve made in already and the installer chooses not to remove it when he pipes it as open.

01-01-2016 12:30PM

my3cents wrote: »

Where does the water go when one of these valves opens?

I can't see it ever opening on a open system fitted by a qualified plumber(who wouldn't fit one anyway:D).

But for those with unvented cylinders they should have the cylinder serviced every year and one of the checks is to see what happens when the safety valves lift.

As someone who inspects unvented cylinders after problems arise I can tell you that 99% of the unvented installations I see risk or have at times caused 10's of 1000s of Euro worth of water damage.

This is due mainly to the T&P valve pipework(if fitted) not being able to handle the volume of water or the very high temperture of the water, in these cases home owners can have a difficult time claiming on their home insurance as the damage was caused by somebody pretending to be a plumber.

K.Flyer · 01-01-2016 02:38PM

depends on how it is plumbed,
have u looked at the schematics on the sytem-link site to make sure its done correctly.

You are also mixing ideas here: expansion and overflow are different concepts.
Yes the flow from the stove should have free access to the overflow pipe which should go straight up to the cold water header tank and the return should be tee'd with a cold water feed from the same tank, again free.
I have replied before on this, as have others so go look.

Which coil on the tank is the stove, top, middle or bottom

To avoid confusion.
It is the Open Vent / Expansion pipe that goes from the heating system up to and overhangs the feed and expansion tank, not the overflow pipe.

Dtp1979 · 01-01-2016 03:51PM

K.Flyer wrote: »

To avoid confusion.
It is the Open Vent / Expansion pipe that goes from the heating system up to and overhangs the feed and expansion tank, not the overflow pipe.

Yes. The overflow pipe goes from the tank directly outside. The pipe that goes up over the small tank and points back into it is the vent. The pipe that comes from the bottom of the small tank is the expansion.

K.Flyer · 01-01-2016 04:39PM

Dtp1979 wrote: »

Yes. The overflow pipe goes from the tank directly outside. The pipe that goes up over the small tank and points back into it is the vent. The pipe that comes from the bottom of the small tank is the feed and expansion.

Wearb · 01-01-2016 07:09PM

All very sharp today lads. Nice to see you hitting the ground running after all the "socialising".

froshtyv · 02-01-2016 01:41PM

Thanks for all the replies.

The cylinder is 100% pressurised. There is an unvented kit fitted for the CWS.
The P&T valve has lifted and due to there being no waste pipe fitted, the water started coming down through the ceiling.

I knew myself something is a miss if the P&T has gone off. I would have a good knowledge of plumbing systems but solid fuel setups wouldn't be my strong front.

I always struggle to comprehend how you can have an open vented solid fuel stove connected straight into a sealed system via a system link with out using a buffer tank, heat exchanger etc.

Ive seen a few mechanical schematics with an "injector T" used, but again i dont fully understand this setup.

So from what i gather from the post above, the whole system should be an open vented system in order for it to operate correctly?

May thanks

Dtp1979 · 02-01-2016 01:43PM

froshtyv wrote: »

Thanks for all the replies.

The cylinder is 100% pressurised. There is an unvented kit fitted for the CWS.
The P&T valve has lifted and due to there being no waste pipe fitted, the water started coming down through the ceiling.

I knew myself something is a miss if the P&T has gone off. I would have a good knowledge of plumbing systems but solid fuel setups wouldn't be my strong front.

I always struggle to comprehend how you can have an open vented solid fuel stove connected straight into a sealed system via a system link with out using a buffer tank, heat exchanger etc.

Ive seen a few mechanical schematics with an "injector T" used, but again i dont fully understand this setup.

So from what i gather from the post above, the whole system should be an open vented system in order for it to operate correctly?

May thanks

What you have is a potential bomb.
It will work but it is extremely unsafe. Yes, both should be open vented.

02-01-2016 02:43PM

froshtyv wrote: »

Thanks for all the replies.

The cylinder is 100% pressurised. There is an unvented kit fitted for the CWS.
The P&T valve has lifted and due to there being no waste pipe fitted, the water started coming down through the ceiling.

I knew myself something is a miss if the P&T has gone off. I would have a good knowledge of plumbing systems but solid fuel setups wouldn't be my strong front.

I always struggle to comprehend how you can have an open vented solid fuel stove connected straight into a sealed system via a system link with out using a buffer tank, heat exchanger etc.

Ive seen a few mechanical schematics with an "injector T" used, but again i dont fully understand this setup.

So from what i gather from the post above, the whole system should be an open vented system in order for it to operate correctly?

May thanks

You cannot have a uncontrollable heat source heating a unvented cylinder.

Most coils in unvented cylinders are not suitable for gravity circuits which would be one of the traditional ways of connecting a stove.

Don't use the stove till you've confirmed the safety of the installation.

The fact your safety valve isn't piped is a indication of shoddy workmanship as the discharge pipework is of fundamental importance when fitting a unvented cylinder.

Also if your cylinder is fitted in the loft has the extra weight of the stored hot water been taken in to account and has it been fitted on marine ply platform to prevent the cylinder from potentially falling through the loft.

froshtyv · 02-01-2016 06:05PM

Thanks for the replies.

Sounds like i am going to get another plumber to fix the situation.

I thought that when the stove was lit, it would gravity feed into the coil in the cylinder, then when the pipe stat was activated it would turn on the stove pump and an associated rads pump to act as a dump circuit.

There is not waste pipe on the P&T valve, safety valve on the system link or on the inlet control valve for the CWS.

The cylinder is a Joule cylinder, im not sure of the model, but im hoping that the coil being used by the solid fuel at present is 1"

Dtp1979 · 02-01-2016 06:15PM

froshtyv wrote: »

Thanks for the replies.

Sounds like i am going to get another plumber to fix the situation.

I thought that when the stove was lit, it would gravity feed into the coil in the cylinder, then when the pipe stat was activated it would turn on the stove pump and an associated rads pump to act as a dump circuit.

There is not waste pipe on the P&T valve, safety valve on the system link or on the inlet control valve for the CWS.

The cylinder is a Joule cylinder, im not sure of the model, but im hoping that the coil being used by the solid fuel at present is 1"

No matter what, you'll have to un pressurise your cylinder.
Water at 2 bar boils at 144'C. A pressurised cylinder sits at 3 bar when cold. Let's say the oil heating had that cylinder at 60'C. You come home, light a big fire, the cylinder temp rises to 102. The P and T valve is blanked by some fool(which I've often seen). The cylinder is prob 5 bar now but the water isn't near its boiling point to bring it to steam.
Then you open a tap, bringing the cylinder back to atmospheric pressure, therefore lowering its boiling point. If you boil 1 litre of water, you get 1600L of steam.
So you've a 300L cylinder of water, with 480,000L of steam (1600x300) trying to escape from it.
Bang

selfbuildpaddy · 13-01-2016 11:04PM

Hi all. I have a question regarding my oil heating/ stove set up and was wondering if anyone else encountered the same issue.

I have a 4 zone system link with (1. Hot water 2. Downstairs rads 3. Upstairs rads 4. Attic rads). When running on the oil boiler all zones heat perfectly through the system link. My stove is located on the ground floor of my house. Once this begins to heat up it heats a buffer cylinder which is located in my attic via gravity loop. Once the stove setpoint is reached on my stove stat located beside my stove, the stove pump which is located beside my system link, also in the attic starts. This will then turn off my oil boiler and start four output pumps of my system link.

The issue I am having is the hot water from the stove is just circulating around my stove, buffer and system link but will not divert out to the 4 zones. There is a non return valve on my oil boiler circuit which means that it is not circulating from the stove through the oil boiler circuit.

Any help would be greatly appreciated, Thanks.

John T Carroll · 15-01-2016 10:50PM

Dtp1979 wrote: »

No matter what, you'll have to un pressurise your cylinder.
Water at 2 bar boils at 144'C. A pressurised cylinder sits at 3 bar when cold. Let's say the oil heating had that cylinder at 60'C. You come home, light a big fire, the cylinder temp rises to 102. The P and T valve is blanked by some fool(which I've often seen). The cylinder is prob 5 bar now but the water isn't near its boiling point to bring it to steam.
Then you open a tap, bringing the cylinder back to atmospheric pressure, therefore lowering its boiling point. If you boil 1 litre of water, you get 1600L of steam.
So you've a 300L cylinder of water, with 480,000L of steam (1600x300) trying to escape from it.
Bang

My understanding of thermodynamics doesnt tie up with the above.
If you have a 300 Litre of water at 5 Bar and 102C and you depressurise it by opening a tap or whatever you will flash off about 1 litre of steam at 100C and you will be left with 299 litres of water sitting in the cylinder at 0 Bar pressure and 100C. That 1 litre of steam will try to occupy a space of 1.67 M3 of space or 1670 litres, if you take a room of average volume of say 25 M3 then while highly dangerous its not of catastrophic consequences and the cylinder will certainly not blow up.
Now, if the solid fuel stove(uncontrolled heating) had heated that 300 Litres of water to its boiling (saturation) point of almost 159C at 5 Bar then in the event of the opening of a tap, 34 litres of steam will (eventually) flash off at 0 Bar and 100C and you will be left with 266 Litres of water sitting in the cylinder at 0 bar pressure and 100C. Now that 34 Litres of steam will occupy over 57 M3 of space, enough to fill a very large room with a steam/water mix at 100C which can certainly cause fatal injuries due to the huge volume it now occupies. Obviously if one opens a tap, one will quickly close it again but if there is a rupture of the cylinder then that can certainly be catastrophic, thats what makes a solid fuel stove/pressurised cylinder potentially so dangerous.
edit: steam is always measured in Kgs but I left it at Litres so as not to cause too much confusion as its the water that flashes into steam.

I can do for sums on the above for anyone who's interested

Dtp1979 · 15-01-2016 11:10PM

John T Carroll wrote: »

My understanding of thermodynamics doesnt tie up with the above.
If you have a 300 Litre of water at 5 Bar and 102C and you depressurise it by opening a tap or whatever you will flash off about 1 litre of steam at 100C and you will be left with 299 litres of water sitting in the cylinder at 0 Bar pressure and 100C. That 1 litre of steam will try to occupy a space of 1.67 M3 of space or 1670 litres, if you take a room of average volume of say 25 M3 then while highly dangerous its not of catastrophic consequences and the cylinder will certainly not blow up.
Now, if the solid fuel stove(uncontrolled heating) had heated that 300 Litres of water to its boiling (saturation) point of almost 159C at 5 Bar then in the event of the opening of a tap, 34 litres of steam will (eventually) flash off at 0 Bar and 100C and you will be left with 266 Litres of water sitting in the cylinder at 0 bar pressure and 100C. Now that 34 Litres of steam will occupy over 57 M3 of space, enough to fill a very large room with a steam/water mix at 100C which can certainly cause fatal injuries due to the huge volume it now occupies. Obviously if one opens a tap, one will quickly close it again but if there is a rupture of the cylinder then that can certainly be catastrophic, thats what makes a solid fuel stove/pressurised cylinder potentially so dangerous.

I can do for sums on the above for anyone who's interested

Interesting point John. You are obviously very well versed on maths and equations. I'm certainly not. But you say 0 bar a few times. The water in the cylinder will never be at 0 bar as its being pumped? Unvented Cylinders have exploded as a result of being heated by uncontrolled heat sources. Can you explain how?

John T Carroll · 15-01-2016 11:31PM

Dtp1979 wrote: »

Interesting point John. You are obviously very well versed on maths and equations. I'm certainly not. But you say 0 bar a few times. The water in the cylinder will never be at 0 bar as its being pumped? Unvented Cylinders have exploded as a result of being heated by uncontrolled heat sources. Can you explain how?

In general, I would say that its a combination of pressure/temperature or may simply be that the expansion allowance isnt sufficient and as water is essentially incompressible then something has to give when the temperature continue to rise. I would like to read some case studies as I havnt come across any despite working (physically) with all sorts of Boilers, Pressure Vessels and Flash Vessels for well over 45 years.

Re the water in the vessel never being at 0 Bar, I used that because thats the example that you used....but it makes no difference really, for example if the pressure in the cylinder was maintained at 5 Bar and was still at 159C and an opening came in the cylinder then as the water is lowered to atmospheric pressure as it exits it will flash off over 11% as steam (the same) and the remainder will be water at 100C, but outside the cylinder, ie you will have 0.89 kgs of water at 100C and 0.11 kgs steam at 100C.

Dtp1979 · 15-01-2016 11:36PM

John T Carroll wrote: »

In general, I would say that its a combination of pressure/temperature or may simply be that the expansion allowance isnt sufficient and as water is essentially incompressible then something has to give when the temperature continue to rise. I would like to read some case studies as I havnt come across any despite working (physically) with all sorts of Boilers, Pressure Vessels and Flash Vessels for well over 45 years.

Re the water in the vessel never being at 0 Bar, I used that because thats the example that you used....but it makes no difference really, for example if the pressure in the cylinder was maintained at 5 Bar and was still at 159C and an opening came in the cylinder then as the water is lowered to atmospheric pressure as it exits it will flash off over 11% as steam (the same) and the remainder will be water at 100C, but outside the cylinder, ie you will have 0.89 kgs of water at 100C and 0.11 kgs steam at 100C.

But how would the 300l @ 159 drop back down to 100?

John T Carroll · 15-01-2016 11:56PM

Dtp1979 wrote: »

But how would the 300l @ 159 drop back down to 100?

That would only happen if there was a rupture of the cylinder (which is the catastrophic case) where all the contents would very quickly fall to atmospheric pressure, but if there wasnt a rupture and one had a controlled opening or a small hole in the cylinder then you will still get a mixture of 0.89 kgs of water and 0.11 kgs of steam for each kg of water but it will be at a much lower rate and will give people time to get out of the way, what kills people is the sudden release of pressure where all the "flashing" can take place almost instantly, and it will if say the top of the cylinder/vessel ruptures, you can only imagine the consequences if a room full of steam is released instantly. There can be very severe damage as well caused by bits of the vessel material being blown everywhere due to the expansion capabilities of steam even at very low pressures down to 5 PSI (0.35 Bar)

I think maybe I should explain the "flashing" with a few numbers. If you have 1 kg of water at 5 bar and 159C then that will contain 671 units (KJ) of heat, if you have 1 kg of water at 0 Bar and 100C then that will only contain 419 units of heat. Now water can only exist at 100C at atmospheric pressure so the kg of water MUST lose (671-419) units of heat, ie 252 units. But where does it disappear to??, it generates some steam, at atmospheric pressure it requires 2257 units of heat to convert 1 Kg of water into 1 kg of steam but as there is only 252 units available or 11.16%, (252/2257)*100, you end up with 0.11 kgs of steam and the rest, 0.89 kgs, as water.
You know all my secrets now, I must go for some refreshments before they close.

John T Carroll · 16-01-2016 12:23PM

Dtp1979 wrote: »

Unvented Cylinders have exploded as a result of being heated by uncontrolled heat sources. Can you explain how?

Thats still a very good question and the answer I gave re the solid fuel stove raising the temperature to 158C or whatever could only happen if the solid fuel system was itself a unvented system with a 3 bar safety valve in which case the temperature in the hot water storage tank could theoretically rise to 142C, still very dangerous from a Flash Steam point of view. If the solid fuel stove is fitted properly with an vented system then the maximum temperature reached may be 105C to 110C depending on the static head before it starts venting into the combined F&E Tank. In my opinion this temperature can be reached whether there is a vented or non vented hot water storage tank fitted so I really cant say why the unvented cylinder is more at risk under these circumstances, if the solid fuel coil was holed for whatever reason then pressurised water from the hot water storage tank would flow into the solid fuel system and could possibly overflow from the C&F Tank if the C&F Tanks own overflow pipe was too small.

Dtp1979 · 16-01-2016 12:36PM

You mentioned earlier about the culinder rupturing that would cause and explosion. How big of a rupture are you talking about? If the p&t valve failed or stuck, and only opened at say 110 degrees, would this cause a bang?

Issue with solid fuel stove connected to Systemlink

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