Hi everyone,
I have a problem I can't get my head around. I have a sink with an Oatey AAV (blue) to vent the pipe. If I screw it on, water trickles down the drain. As soon as I remove it, it drains fast. I thought it was broken so I bought another one from Studor. Same issue. So I opened the Oatey AAV to check and everything is fine. I checked for positive pressure in the pipe and it seems fine. All pipes are ABS, and threaded fittings are taped. Main to which it is connected is vented to the roof. Height of the AAV is as drawn.

Any ideas why it doesn't drain

 

Take off the AAV and gently suck & blow into it to make sure the valve is open. I have seen a few older ones that stick a bit. Often just cleaning the seal area is enough to get them working but I've never had a brand new one stick.

 

Thank you for your reply. I tried and even bought another one. None one them work once installed on the pipe but they both mechanically work

 

I had the exact same problem about a year ago. I can 95% guarantee it's a partial clog on the rain, probably below the slab. As soon as the clog is removed, it'll flow as you expect.

It doesn't make sense initially, but I'm pretty sure that's your problem.

 

I'll give it a try with a drum auger. I still can't figure out why it would work when I remove the AAV. It's worth a try

 

Hi Mat –

I’m no plumber and no expert. I just follow these threads for exercise to try and keep my elderly brain from deteriorating any further – or I guess maybe slow it down a little anyway, lol. I was wondering also what would explain what you are seeing. I found articles out there on AAV but I was hoping to see some diagrams or videos with arrows and flows etc. at certain system points to explain the plumbing venting process in general. I couldn’t find any – with arrows, etc. that is.

But I found stuff out there talking about positive pressures, negative pressures, etc in the draining process. I think some of them are a little hard to follow.

Anyway, what I could glean from what I saw was that AAV valves are normally closed but open up and admit air when there is a negative pressure in the pipe. The negative pressure would be caused when the water starts to flow down the pipe. I guess it really is just a sucking caused by the water flow. That suction would open up the AAV valve and let air in and the proper water flow would occur.

But if for some reason the water flow isn’t strong enough, hence the suction not strong enough, the AAV valve would not open properly and without the proper added air from the AAV the water flow would be even more impeded. I guess much more impeded.

So with the AAV removed, a partially blocked drain would actually drain better because it would be getting more air than it would with the AAV connected on the pipe. So that would explain what Zorfdt identified in post # 4.

I have no idea if any of the above is correct – but it sounds pretty good – lol.

Hope you can post back when you get things working and let us know. Good luck!