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mrfixit

Moderator

Posts: 1,987

Location: USA

21

Friday, June 24th 2016, 11:23am

I fixed his link. It's not a valve at all. Looks like a vaccum breaker to me.

Maybe valve 5 is the only one coming off of the house.

Wet_Boots

Supreme Member

Posts: 5,123

Location: Metro NYC

22

Friday, June 24th 2016, 5:15pm

I think that could be a phenomenon of too much system demand combined with under-sized supply plumbing, although that might be its own unique oscillation event. It takes a fairly low supply pressure to get a pressure vacuum breaker to dump, and it can happen when two zones are on at the same time, although there is usually more banging noise in the plumbing. I've heard of, from customers of systems I maintain, but did not install, of much stronger and slower cycles with that same PVB, with the dump water coming out so forcefully that it washed away some of the soil beneath the PVB.

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