Now stocking PT-BOX and PT-300. The air admittance valve box from Ayrlett comes with a PVC 20 DFU air admittance valve mounted in a utility box ready to install. The box also comes standard with a 1-1/2 in. – 2 in. adapter, a protective plastic cover to prevent debris from entering the vent during installation and a sturdy louvered cover. Air admittance valves (AAVs) are one way valves that allow air in, to vent or equalize pressure in waste pipes, without allowing gases, odors or liquid out. Our AAVs have been tested by an independent U.S. lab 500,000 cycles, in temperatures ranging from -40°F to 150°F, without a single failure.