So we had remodled our ensuite a few years ago, and decided to reconfigure at that time as well as go from 1 sink to 2.

Due to the reconfiguration I knew I wasnt going to be able to use the existing stack for venting and was pretty sure that tapping into the bathtub venting wouldnt work as it would be too far away.. sure enough it was.. and we would get air lock in both sinks but they would eventually drain just at about a 20% rate from before.

So Ive gone ahead and installed an AAV to resolve this and the right hand sink drains with no issue now but the left hand sink wont drain at all now.. Both sinks have independant p traps.. Im not sure why it wont drain with the AAV and why it wont even drain like it did before (just slowly)

any thoughts? Did I need to install the AAV closer?

 

Try removing the drain stopper from the problem sink and see if it drains.

 

yes, Ive tried that and it doesnt help.. its completely out.. also tried plugging it and it doesnt help.. if I remove the white cap of the AAV the left sink will fully drain quickly but most of that water comes out of where I just removed the white cap from.

 

AAV's have different DFU ratings. You need an AAV rated to handle a low amount such as just 2 DFU. It's possible that the DFU rating is affecting its performance. Also should have been higher... Not sure about closer but it's possible it should be closer too.

 

ok some more info.. the water flow (drainage) goes from left to right in my setup.

The height I have for the AAV is 5 inches from the top of the horizontal pipe to the bottom of the white valve.. the minimum the mfg recommends was 4 inches.

The AAV that Im using is the Oatey Sure-Vent, which I think is rated properly for this setup.

 

Here is a little more info for you. Oatey makes 4 sizes of AAV Sure-vent. Which do you have? Hopefully it is the smallest rated one that they make. Using the smallest DFU for your application will help ensure it works properly. Just because it says AAV on the package doesn't mean it is right for any application.

And 4" is a minimum. You always want to install them as high as is possible and typically as close to the trap source as possible. Minimum means just that. It's not the recommended height, it's the minimum. You don't put them near minimum unless that's as high as you can possibly go. You put them as high as possible so that they are less likely to ever get plugged and fouled when your sewer backs up.

https://youtu.be/Ffbka3FriQY

 

A big issue is the water coming up out of your AAV when the valve is removed. That indicates that there is a restriction in the drain line somewhere downstream. The drain pipe cannot take the water as fast as it's coming out of the sink. Does the drain line have proper fall? Is there a second trap in the line? Is there a partial clogg?

Always mount the AAV as high as you can get it no matter what the instructions say about a minimum. Higher is better.

The reason the size of AAV is important is the opening force. It is a mechanical one way valve and it takes a certain vacuum force to open the valve. Large valves require more suction to open like from the huge slug of water when a toilet flushes. The relatively small vacuum created by a sink draining likely is not enough to open a big valve. Smaller valves intended for a sink will open with the slightest vacuum and might help with your issue.

 

I agree with Pilot Dane, the fact that the water overflows out of the AAV pipe when you remove it indicates a clog further down the line to me. It's not fully intuitive, but an AAV coupled with a partial clog can make the drains quite slow.

 

Thanks for all your thoughts so far.. here is a crude drawing of my existing setup. The Oatey Sure-Vent I have is the one rated for 160DFU branch, 24DFU Stack, model #39018. Im not too sure about there being a blockage however as the right hand sink does drain properly now that the vent has been installed.. But the left hand sink still doesnt.
I am thinking I will do two things, the first is install another vent as close to the p trap on the left hand sink as I can and make sure both vents are as high as they can be. Just have to know if I have the right type of AAV for this application