Kilt Posted January 30, 2021 Share Posted January 30, 2021 (edited) We’ve just had a new manifold installed on our water supply, to provide us with Toby’s, but there is a dead leg to end of manifold, attaching it to a unused pipe. Leg is maybe 400mm-1000mm in length. we have a private break tank and private pumps, but original water comes from local board, so water is treated. the manifold supplies several properties, so there’s a lot of water flowing through it. im going to go back to installer of manifold and ask same question, but wanted a few extra (better) brains on matter. Is the dead leg anything to worry about? 50-60mm mdpe at 400mm is what about 1 litre? Edited January 30, 2021 by Kilt Link to comment Share on other sites More sharing options...
ProDave Posted January 30, 2021 Share Posted January 30, 2021 Are you saying there is one pump feeding into a manifold that feeds several properties? The only time I have seen this before each property had it's own pump in the break tank so all separate. Link to comment Share on other sites More sharing options...
Kilt Posted January 30, 2021 Author Share Posted January 30, 2021 (edited) 6 minutes ago, ProDave said: Are you saying there is one pump feeding into a manifold that feeds several properties? The only time I have seen this before each property had it's own pump in the break tank so all separate. Two pumps running in tandem. They’re set to 4 bar and we don’t have any pressure issues. however life would be so much simpler if we did have a tank & pump per property! ? Edited January 30, 2021 by Kilt Link to comment Share on other sites More sharing options...
Nickfromwales Posted January 31, 2021 Share Posted January 31, 2021 21 hours ago, Kilt said: We’ve just had a new manifold installed on our water supply, to provide us with Toby’s, but there is a dead leg to end of manifold, attaching it to a unused pipe. Leg is maybe 400mm-1000mm in length. we have a private break tank and private pumps, but original water comes from local board, so water is treated. the manifold supplies several properties, so there’s a lot of water flowing through it. im going to go back to installer of manifold and ask same question, but wanted a few extra (better) brains on matter. Is the dead leg anything to worry about? 50-60mm mdpe at 400mm is what about 1 litre? Fresh disinfected water will be passing this, so I would not worry. The metabolism says the risk is minute. Link to comment Share on other sites More sharing options...
TonyT Posted January 31, 2021 Share Posted January 31, 2021 Agree with risk being minimal, chlorinated water under 20deg, if an L8 risk assessment was to be carried out it would advise the dead leg shouldn’t be more 2x the diameter of the pipe. Link to comment Share on other sites More sharing options...
TonyT Posted January 31, 2021 Share Posted January 31, 2021 So as it’s a new install I would ask them to rectify. Link to comment Share on other sites More sharing options...
Nickfromwales Posted January 31, 2021 Share Posted January 31, 2021 (edited) 8 minutes ago, TonyT said: Agree with risk being minimal, chlorinated water under 20deg, if an L8 risk assessment was to be carried out it would advise the dead leg shouldn’t be more 2x the diameter of the pipe. Over what distance? This is just a short branch. Edited January 31, 2021 by Nickfromwales Link to comment Share on other sites More sharing options...
TonyT Posted January 31, 2021 Share Posted January 31, 2021 When I did my city and guilds legionella courses they advised that the short branch , the water isn’t scoured out if it’s more than 2 x times the diameter, so effectively the last fitting where water is drawn off, in this situation pipe shouldn’t extend more than 100/120mm my plumbers did another course with me, and again this was reiterated but they advised they didn’t get this info at college during apprenticeship L8’s a good money spinner for some companies , disinfecting tanks, shower heads etc , that’s why we do all our estate in house. Link to comment Share on other sites More sharing options...
Conor Posted January 31, 2021 Share Posted January 31, 2021 We (water mains designers) try to keep dead legs under 5x the pipe diameter. E.g a 50mm ID capped pipe would have to be 250mm or less in length. At this length turbulence is sufficient to refresh the water in the leg. Any longer, and the water will be stale and potentially harbour bacteria. However, if you have a way to flush out the leg, then it doesn't really matter as the risk only presents when for some reason the dead water enters the rest of the pipe network. Fyi I've seem some terrifyingly dirty water washed out of hydrants and scour pipes in my time. I'm amazed I still drink tap water Link to comment Share on other sites More sharing options...
Kilt Posted January 31, 2021 Author Share Posted January 31, 2021 (edited) 3 hours ago, TonyT said: So as it’s a new install I would ask them to rectify. New manifold on a old pre-existing system. I underestimated the length, measured today and it’s just over a meter of pipe that’s unused. Edited January 31, 2021 by Kilt Link to comment Share on other sites More sharing options...
Nickfromwales Posted February 1, 2021 Share Posted February 1, 2021 (edited) Sitting down from the upper moving rail of water, that is a very dead leg. As it's not true potable water, I think I'd want that gone. Edited February 1, 2021 by Nickfromwales Link to comment Share on other sites More sharing options...
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