How big is your bucket? (aka PRV collection vessel.)

[Pip]

It may sound a trivial question, but here goes.

I have as I should, directed my Pressure Relief Valve on my solar loop so that if it should operate, the outfall goes into a collection vessel.  I know from photos in the forum, many people just sick a bucket under it, however in my situation due to space limitations I would like to keep the said “bucket” as small as possible.  My heat dump radiator is actually a meter below the EV and PRV so I know that I can leave that out of the calculation. 

So should I allow for a minimal outfall in the case of stagnation, or should I allow capacity for the whole of the loop that is above the PRV.

Any suggestions welcome, and out of interest, has anyone in the forum actually seen a situation where the PRV has activated.

Cheers
Pip

[CeeBee]

This ain't going to help but: Mine's a B&Q special orange plastic job - I guess about 2 gallon. Didn't even know what it was for until I emailed Tony Stone saying "You seem to have left your bucket behind (and inspection lamp) - I've put it aside for when you call round". The EV and PRV are in the loft but on the end of a pipe which is teed off low down, so they shouldn't get to see hot water. In my case, I expect that's more volume than is in the entire system. No evidence that it's ever been in action. Not sure what volume might be expected. If no steam in the system (so EV should really be taking the extra) then a tiny release will give a large relief of pressure. In the steam situation, you hope that the volume needed is just enough to empty the manifold. Still doesn't sound much to me. And if all else fails, all you get is a bit of water somewhere it's not supposed to be, but a limited amount - the volume of the system at absolute worst.

[martin W]

Well I suppose sensibilly you should have a bucket big enought to contain all the fluid in the solar system that could be pumped. BTW should'nt the container be metal and not plastic that could melt and or deform and let the hot contents out?

[Hugo]

AS my E V was in the loft as well I went for a pipe to the outside and into a tundish.
That way there are no worries.

[wookey]

Mine is a 5l aliminium cylindrical tin (I happend to have, previously holding useful items). My entire solar loop volume is 4.5l.

Exactly how much water you would get ejected in case of overpresure depends on the total system volume, the expansion vessel size, the expansion vessel pressure, then system pressure and the height the PRV tee's off at. A correctly designed domestic system should be able to take it all up in the EV and thus not emit any water (this works OK on mine). If for some reason extra steam got produced (e..g because the pump was still running on full and thus pumping against steam pressure, but the heat was not being removed) then you could get enough steam volume to overwhelm the EV, trigger the PRV and let some water out. Clearly it can't possibly be more than the total system volume, and it probably won't be more than 'a bit' which allows the pressure to drop enough to close the valve. Again only if steam production continues will more water come out, probably up to the portion of the system above the take-off point, but steam might push more out.

So a genuinely fail-safe vessel needs to hold whole system volume. One that hols a few litres (3?) will be OK in all but the worst case.

[Pip]

Mine is a 5l aliminium cylindrical tin (I happend to have, previously holding useful items). My entire solar loop volume is 4.5l.

Exactly how much water you would get ejected in case of overpresure depends on the total system volume, the expansion vessel size, the expansion vessel pressure, then system pressure and the height the PRV tee's off at. A correctly designed domestic system should be able to take it all up in the EV and thus not emit any water (this works OK on mine). If for some reason extra steam got produced (e..g because the pump was still running on full and thus pumping against steam pressure, but the heat was not being removed) then you could get enough steam volume to overwhelm the EV, trigger the PRV and let some water out. Clearly it can't possibly be more than the total system volume, and it probably won't be more than 'a bit' which allows the pressure to drop enough to close the valve. Again only if steam production continues will more water come out, probably up to the portion of the system above the take-off point, but steam might push more out.

So a genuinely fail-safe vessel needs to hold whole system volume. One that hols a few litres (3?) will be OK in all but the worst case.

Thanks Wookey, I think you have pretty much summed up my feelings.  In worst case and I had an over flow, it would do no harm, just wash my cellar steps with water and antifreeze, the latter being the reason for the capture in the first place.

[Brandon]

AS my E V was in the loft as well I went for a pipe to the outside and into a tundish.
That way there are no worries.

anti freeze is, I believe considered a pollutant...

[Vollster]

I just bought a 4 gallon cold water tank for this job (with lid so hopefully nobody will feel inclined to move it if there is  a copper pipe going into it!).  However I am not sure whether or not it would stand up to the temperature of the water that would be likely to come out of a pressure release valve although as pointed out already it would only be likely to be a small amount and at 100 centigrade as otherwise it would be steam (or does glycol do something odd to the water and allow it to be liquid at temps higher than 100C. 

Any views?  Has anyone got any ideas of a way of testing it at temperatures other than through water boiled in a kettle?

[Pip]

AS my E V was in the loft as well I went for a pipe to the outside and into a tundish.
That way there are no worries.

anti freeze is, I believe considered a pollutant...

In an early thread there was a discussion about types of antifreeze and other additives in the system such as inhibitor.  But in a nut shell, the type of antifreeze that should be in the solar loop is Propylene Glycol which is considered non toxic, unlike the stuff used in the automotive industry which is Ethylene Glycol and highly toxic, and if ingested can be fatal.
http://www.navitron.org.uk/forum/index.php/topic,6693.msg72735.html#msg72735

What ever is in the system, it seems to be the accepted practice to capture any outfall, not least to see if there has been an over preasure incident.  In many cases it is less hassle to do this rather than run a pipe via a tundish to a suitable drain.

Some people have been known to take spontaneous showers in the stuff, coming out a nice purple colour :
http://www.navitron.org.uk/forum/index.php/topic,6693.msg72776.html#msg72776 

[gus]

For such things as combi's/pressurised heating system's I believe that the regs say you can have the PRV going into a bucket/container but the bucket/container must be made of metal ! And BTW it took me ages to find one ! Everything seems to be plastic now-a-days

[Amy]

and yet the vailant solar system i fitted 2 years ago suggested the PRV was vented into the top of an empty 5 gall glycol drum

[chickensoup]

For such things as combi's/pressurised heating system's I believe that the regs say you can have the PRV going into a bucket/container but the bucket/container must be made of metal ! And BTW it took me ages to find one ! Everything seems to be plastic now-a-days

 Gus,
        The regs state that the prv's attached to combis and sealed systems have to be terminated externally against the wall( not above a window/door or air vent) or low level on the ground.............thats in the British standards. I have to correct you as that is extremely dangerous...................there is a lot more water in a heating system.

               chicko

[martin W]

For such things as combi's/pressurised heating system's I believe that the regs say you can have the PRV going into a bucket/container but the bucket/container must be made of metal ! And BTW it took me ages to find one ! Everything seems to be plastic now-a-days

Found nice galvanised 2 gallon one in local garden centre for £6 (yes I did say £6). Would galv react with the propylene Glycol?

[martin W]

For such things as combi's/pressurised heating system's I believe that the regs say you can have the PRV going into a bucket/container but the bucket/container must be made of metal ! And BTW it took me ages to find one ! Everything seems to be plastic now-a-days

 Gus,
        The regs state that the prv's attached to combis and sealed systems have to be terminated externally against the wall( not above a window/door or air vent) or low level on the ground.............thats in the British standards. I have to correct you as that is extremely dangerous...................there is a lot more water in a heating system.

               chicko

Does that mean the Solar must also be vented externally as it is a sealed system. I am sure it must be vented into a tundish, but I don't know if it *must* be vented externally. (maybe bucket with overflow?) Wouldn't a container that had more capacity than the circuit it was collecting from satisfy the regs without the need to vent the fluid externally?

[chickensoup]

 Martin,
           Nobody YET is policing solar, so you can do as you like on the wet side.

     chicko