We recently bought an older house, with plumbing that was updated about 10 years ago. A problem we found was that the kitchen sink drains very slowly. When I looked at the DWV plumbing, I found something very strange: there was what looked sort of like a loop vent...but with no vent connection, it just looped back to the drain line. Similar to the diagram of a Chicago loop on Wikipedia, if you crossed out the vent connection. Was there a reason for this that I don't understand, or was this as pointless as it looked?
Anyway, I guessed that the slow draining was caused by a lack of proper venting, so I took out the loop, planning to replace it with an air admittance valve. (Yes, they're permitted here.) I tried the drain while the vent lines were wide open, and it drained great. But with the AAV in place, it drained as slow as before.
By temporarily removing the AAV and taping a plastic bag over the vent line instead, I discovered that, when the sink drains, a POSITIVE air pressure is created at the vent, which must have caused the AAV to close, so that I still effectively have an unvented drain whenever the sink is in actual use. Now I'm not sure what to do. Installing a real vent out the roof would mean tearing out cabinetry and opening the wall, which I really want to avoid. (Plus, there's a wide window over the sink, which the vent line would have to go around.) But I can't think of any other options, either.
Anyone have any suggestions?
Thanks,
Paul
Anyway, I guessed that the slow draining was caused by a lack of proper venting, so I took out the loop, planning to replace it with an air admittance valve. (Yes, they're permitted here.) I tried the drain while the vent lines were wide open, and it drained great. But with the AAV in place, it drained as slow as before.
By temporarily removing the AAV and taping a plastic bag over the vent line instead, I discovered that, when the sink drains, a POSITIVE air pressure is created at the vent, which must have caused the AAV to close, so that I still effectively have an unvented drain whenever the sink is in actual use. Now I'm not sure what to do. Installing a real vent out the roof would mean tearing out cabinetry and opening the wall, which I really want to avoid. (Plus, there's a wide window over the sink, which the vent line would have to go around.) But I can't think of any other options, either.
Anyone have any suggestions?
Thanks,
Paul