Air Admittance Valve seems to be a problem

[Brian in Virginia]

A friend called about slow drainage in his double kitchen sink. When the dishwasher empties, water backs up into both bowls. When I remove the AAV, water flows freely--no problems, even during dishwasher discharge.
I replaced the Studor Mini-Vent with a new one but the same problem returned. When I stop either drain, fill with water and remove the stopper, the water drains slowly with the Studor in place abut will flow freely when it is removed. Just to be sure, I purchased an Oatey Sure-Vent and replaced he Studor. That did not fix the problem. I'm including a photo of the under sink setup. The homeowner says this is a new problem. (I disconnected and cleaned all of the PVC pipes going to the stack. )

 

[FullySprinklered]

Only thing obviously wrong is your dishwasher discharge line. It should loop up before connecting to the disposer. That has nothing to do with your slow drain issue.
The only thing I see that could be a problem is where your trap arm goes into the trap adapter. If the trap arm is too long, it may be dead-ended into the back side of the tee, constricting the outflow from the sink. Pull that fucker out and shorten it, if that's the case.

 

[Sponsor]

 

[Brian in Virginia]

Only thing obviously wrong is your dishwasher discharge line. It should loop up before connecting to the disposer. That has nothing to do with your slow drain issue.
The only thing I see that could be a problem is where your trap arm goes into the trap adapter. If the trap arm is too long, it may be dead-ended into the back side of the tee, constricting the outflow from the sink. Pull that fucker out and shorten it, if that's the case.

Thanks. I'll take a look at the trap arm. However, when the AAV is off, the water flows freely.

 

[MKS]

Terry has mentioned in simaler posts that there needs to be a vent for the drain system through the roof for the aav to work correctly I believe.
Might be good to check what is going on below the cabinet floor with this drain line also.

 

[Brian in Virginia]

Terry has mentioned in simaler posts that there needs to be a vent for the drain system through the roof for the aav to work correctly I believe.
Might be good to check what is going on below the cabinet floor with this drain line also.

Thanks for the suggestion. I did read in the Oatey instructions that there needs to be a vent through the roof. I am going over on Saturday to check the second vent situation. My friend says this is a new problem, so I'll be checking the whole system again. I've got another AAV that I know works, so I'll try that first.

 

[ReginaTy]

Thanks for the suggestion. I did read in the Oatey instructions that there needs to be a vent through the roof. I am going over on Saturday to check the second vent situation. My friend says this is a new problem, so I'll be checking the whole system again. I've got another AAV that I know works, so I'll try that first.

 

[ReginaTy]

I have ran into this exact problem but only on a single compartment. The issue can be solved by a similar aav valve that is used in a case of positive pressure. What seems to be occuring is that the air pressure when the sink goes to drain, is pushing the valve closed which would happen in a similar situation like a check valve. It then doesmt allow it to open back up for it to drain again. You should be able to solve the problem with that device or what i am going to try is creating almost an island vent loop to allow the water to start draining and create a negative pressure in the plumbing system

 

[Plumber69]

get your drain snaked.

 

[hj]

The drain is obstructed. Removing the AAV eliminates the SYMPTOM, not the problem.

 

[Plumber69]

negative slope will cause your symptoms.

 

[FullySprinklered]

Noticed something just this week that I didn't know before. AAVs have a DFU rating. In other words, they need to be sized for the fixture(s) being serviced.