Its purpose is to equalize pressure in the pipes and prevent a vacuum from forming as the fixture drains.
The vents allow air into the drain pipes to help keep the drain flowing properly.
Sometimes, though, it is difficult to connect fixture drains directly to an external vent pipe.
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In mobile homes, for example, there may be no external vents at all.
In these instances, an alternative method of equalizing air pressure is required.
This is where the AAV comes in.
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With this negative pressure dissipated, the water in the drain trap cannot be siphoned off.
Tip
Rules on the use of AAVs vary widely from state to state.
Other states limit the number of AAVs that a single home can use.
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Always check with your local building inspections office for advice on what venting strategies are allowed.
Some sinks will give hints that an AAV is necessary.
Adding an AAV often resolves these issues.
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If the drain already has an AAV, such symptoms might indicate that the valve needs to be replaced.
This will give you plenty of room to work comfortably.
A bucket is useful to catch water in the drain trap as you remove it.
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This will involve cutting sections of PVC pipe, and may also involve shortening the trap arm.
Careful measurements are required.
If allowed by local codes, the auto vent should be installed above the flood-level rim of the fixture.
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This key in of installation is not always easy in situations where the walls are closed.
This will help you quickly align the parts correctly as you solvent glue them together.
Attach the air admittance valve to the top of the vertical extension pipe extending from the sanitary tee.
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Some form of transition fitting may be required to allow the trap arm to fit the sanitary tee.
Join the trap arm to the trap bend, but leave the slip nut loose at this point.
When the pieces are properly aligned, tighten down all slip nuts, using channel-lock pliers.
If necessary, tighten any leaking slip joints with channel-lock pliers.
