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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?

plumbing venting

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    You have a clog/low clearance somewhere. – DMoore Mar 24 at 3:26
  • In the vents or in the wet drain pipes? Or could it be either? – littleturtle Mar 24 at 3:42
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    Drains - for sure. Could be a slight clog but that's it. AAV lets in more air and might help some things drain faster, there is a clog/clearance issue, air isn't moving with the discard, so travels up to the spot of the greatest ease. – DMoore Mar 24 at 3:44
  • Given the comments above I also can't be sure that a weaker AAV will help - theoretically it could but getting something half the admittance probably will still have same issue. But doing this is like complaining about a bleeding finger so you numb your whole arm. Now saying that, finding/fixing this clog may be a task in futility. These things are hard to fix sometimes minus replacing everything with PVC (guessing you have some old metal/iron). – DMoore Mar 24 at 4:36
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    How do you permit excess gas to exit your plumbing system? Seems like it would have no choice but to push water out of a trap somewhere. I.e. Gurgling. Put it this way, why would those pipes need roof penetrations if they were only intakes? – Harper Mar 26 at 21:17
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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

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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.

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When the laundry drains, it pushes a slug of water with air in front of it. That air wants to go up, not "down" the main drain, which is one reason why the roof vents are there. Once the slug passes the branch where the roof vent is, the situation changes and the slug wants to pull some air behind it as it finishes it journey down the drain. This is the other reason the roof vent is there (so as not to pull the "plug of water" out of p-traps). The AAV can't juggle these demands like an open roof vent because it is only a one-way device. With the AAV installed, the slug of water draining from the laundry is pulling air past the water in the kitchen sink trap and it glugs.

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