I recently installed Studor Mini-Vent air admittance valves (AAVs) in my attic on the two secondary (2 inch) plumbing vents (serving laundry room and kitchen) so that the vents no longer penetrate the roof. After doing this, my kitchen sink gurgles whenever the clothes washer drains into the laundry standpipe. If I remove the AAV on the laundry vent, the gurgling no longer happens, so it doesn't seem like there is a blocked vent.
I tested the AAV with my mouth and it seems to be working properly.
My only guess is that the AAVs require more pressure to open than the pressure required to gurgle the sink. Should I look for "weaker" AAVs? Would installing an AAV by the kitchen sink help eliminate the gurgling?
Best Answer
There is a blockage downstream of the kitchen. AAV allow air to enter the system and not exit. Plumbing systems are a neutral pressure system and the vent equalizes the pressure on the back side of the waste water. As the water from your laundry goes down the drain the blockage causes a pressure build up that the AAV no longer allows to escape. Removing the AAV allows the air to escape up the vent pipe.
One other possibility is a main waste line trap with the vent removed.
Main waste cleanout
Chest of Books
Some houses still have a set up like this. In this picture the vent is on your lawn and the clean-out is under the sidewalk or street. Often people remove the vent because it looks like some weird piece of metal with a cap on it sticking out of the lawn. With that vent gone and AAVs added top the air has nowhere to escape. This is an unlikely scenario but it is possible.