The AAV (air admittance valve) simply lets air into your sink’s drainage pipe. Air is important as it helps balance the air pressure in the pipe enough for the waste water to easily drain out. It is similar to what a venting system does.
However, venting systems are tedious to install and could even be next to impossible in certain situations like home renovations or mobile homes. In cases like this, the alternative is its less cumbersome counterpart: The AAV.
How an AAV functions
A lack of air supply in drainage pipes pushes air out of them causing pressure to build up. This pressure could push sewage back into your house, leading to clogged-up drainage, and requiring the services of an emergency plumber. Pressure build-ups could also suck out the fluid in the P-traps.
If you have ever seen a U-shaped arrangement in any plumbing fixture, that is a P-trap. P-traps hold an amount of water in them so sewer gases don’t flow into the house. Therefore, dried-up P-traps allow dangerous gases up from the sewers and into the home. These gases (Mostly methane) are dangerous and could go as far as to cause explosions, plus, they are smelly.
An AAV employs gravity and air pressure to maintain sufficient air pressure within these pipes. It does this by opening up during the drainage process, when the air pressure is low, and closing as soon as the pressure balances. Additionally, when the valve closes, it blocks off sewer gases that might be waiting to sneak into your sink.
Installing an AAV
There are codes in place to guide or permit AAV installations. So, before you begin, you need to go through those codes.
AAVs are portable, cylindrical objects with spaces that are meant to allow air into them. This implies that they should normally be installed in the open (they shouldn’t be covered by walls or insulated). An AAV is usually installed vertically between the P-trap and the drainage pipe.
Furthermore, AAVs should usually be a few inches above every pipe. For general installations, this value is usually never below 4 inches above the sanitary tee it is to be installed in. This might require you to add a connecting pipe measured accordingly.
Next, screw-in or glue the AAV in place depending on the manufacturer’s instructions and you are good to go.
To be sure the AAV you have just installed functions well, the best thing to do is test it. To do that, you could turn on the tap or flush the toilet while listening for any sound or indication of sewage backflow.
However, before testing , you should know that AAVs make a low, thunking noise that comes from the vents opening to let in air and closing to block off the supply. However, for more expertise on the matter, it is always advised to get the services of a plumber.