A sink air vent, more accurately called an air admittance valve (AAV), functions by allowing air into the drain pipe to prevent a vacuum from forming when water drains. This prevents the siphoning of water from the sink's P-trap.
Here's a breakdown of how it works:
- Negative Pressure: When water drains from the sink, it creates negative pressure (suction) inside the drainpipe.
- AAV Activation: This negative pressure pulls the AAV's internal mechanism open. According to the reference, the valve opens "to admit room air into the drain under the force of the negative pressure caused by water flowing through the drain" (04-Apr-2022).
- Air Intake: The open AAV allows air to enter the drainpipe, equalizing the pressure.
- Preventing Siphoning: By introducing air, the AAV breaks the vacuum and prevents the siphoning of water from the P-trap.
- Valve Closure: Once the water flow stops and the pressure equalizes, the AAV's mechanism closes, preventing sewer gases from escaping into the room.
