Air Admittance Valves (often shortened to AAV or called Cheater Vents) are compact plumbing components which are designed to allow air into a drain/waste/vent pipe. Your home’s plumbing drainage system requires open airflow to function properly. If a vacuum were to occur where an air bubble keeps water from draining, it could cause water to back up into an otherwise functional system.
On a less severe end of the spectrum, some drains can gurgle and burp when running a lot of water down the drain system. This gurgling is especially common with older houses, homes with smaller drain pipes than are used in current construction practices, homes where a high capacity washing machine is draining more water than was accounted for when the home was built, homes with a sink or tub far from the main sewer connection, and homes with few roof plumbing vents. The gurgling is not necessarily a sign of trouble, it just means the pipes are accepting air in a less efficient way than modern homes are designed for. But it could create a vacuum which removes all standing water from the P-Trap under your sink. That P-Trap is intended to keep water in it so that smelly sewer gasses do not come up your drain pipes.
AAVs are considered by some to be a last resort and may not be allowed in all areas. Ideally, there should be sufficient roof vents connected into the drainage system as designed by a plumber – but when that is not possible, an AAV could be a solution a plumber recommends. Usually, they are put to use in an older home that is being remodeled with new fixtures or on a kitchen island that includes a sink drain but no easy access for a plumbing vent to be installed.
There are alternatives, and Air Admittance Valves do have a limited life expectancy. In general, they work with a gasket that is opened when negative pressure occurs inside the drain pipe, which occurs when a sufficient volume of water is drained. The gasket should close when pressure returns to normal. They are designed not to allow water or air back out of the system when installed properly by a licensed plumber according to manufacturer directions, but there is some question in my mind what happens when a valve reaches its end of life. As such, seek the guidance of a licensed plumber!
Too long, didn’t read version: AAVs allow air into your drain so it works better.
-Marshall Tramp, CPI, RMP
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