Unusual pressure safety valve installation

System

This discussion was created from comments split from: **The wtf plumbing thread**.
MOD NOTE. I moved this to a new thread. It has become more than just a wtf post.

Calahonda52

Any thoughts on the PRV plumbing here

It goes up into the attic and bends over the Cold water tank

Andy From Sligo

https://www.boards.ie/discussion/comment/119649830#Comment_119649830

Well i suppose if it works its neater to have all that expanded water from the PRV exit into the tank in the attic rather than all out into the hot press.

Actually though, come to think of it when / if that PRV does open, all that yucky black central heating dirty water will go into the clean water of the header tank in the attic - so yeah, not a good idea.

they would better to put a small header tank next to the large header tank even though the CH is of sealed type and put a overflow pipe leading to outside - or even just extend that overflow pipe from the PRV thats bending over the header tank and bring it to the outside under the eaves so that if PRV ever does open it can just exit outside the house

wiz569

That looks like the prv from a sealed dhw cylinder so no yucky heating water, the only trouble with it is you won't know when it's passing till the tank in the attic starts overflowing, if they had no other option they should have fitted a tun dish so you could at least see when it's passing.

Dtp1979

https://www.boards.ie/discussion/comment/119649830#Comment_119649830

https://www.boards.ie/discussion/comment/119651204#Comment_119651204

In that particular scenario a tundish wouldn’t work.

what they did was a total diy job. I’m surprised they didn’t blank it off.

the tank upstairs won’t overflow either as mentioned about as any water released from the prv will be replaced. It’s just circulating.

solution: find out why the prv is passing water. Pipe it outside in copper.

Charlie19

It be interesting to see the rest of that install.

wiz569

https://www.boards.ie/discussion/comment/119652407#Comment_119652407

Stupid me of course it would just circulate,

but the tun dish would at least make it obvious it's passing no?

Obviously it's not the correct way to install regardless.

Dtp1979

https://www.boards.ie/discussion/comment/119653037#Comment_119653037

I’m all for using a tundish but in this case how would it work if the pipework was rising up higher? All the water would overflow out of the tundish

wiz569

Yep that's another D'oh moment, sorry m8.

whizbang

Prv quite often only pass a small amount of water regularly. In this case you will have the water standing in the pipe, eventually drying/congealing and blocking the pipe.

dathi

i took this from joules installation guide.

When operating normally water will not be discharged. Water discharge from the two safety valves will only occur under fault conditions. The tundish should be vertical, located in the same space as the unvented hot water storage system and be fitted as close as possible, and lower than the valve, with no more than 600mm between the safety device outlet e.g. the temperature relief valve and the tundish. The position of the tundish must be that when installed it is visible to the occupants of the premises. When positioning the tundish, the drain valves and motorised valve ensure that these items are positioned away from any electrical devices. The discharge pipe (D2) coming from the tundish should terminate in a safe place where there is no risk to persons in the vicinity of the discharge, be of metal and: • Be at least one pipe size larger than the nominal outlet size of the safety device unless its total equivalent hydraulic resistance exceeds that of a straight pipe 9m long, i.e. discharge pipes between 9m and 18m equivalent resistance length should be at least two sizes larger than the nominal outlet size of the safety device, between 18 and 27m at least 3 sizes larger, and so on