Oatey Sure-Vent Air Admittance Valves provide the ideal venting solution for island sinks, remote bathrooms and remodel jobs by eliminating the need for a stack vent. They are designed to block sewer gases in DWV systems by opening and closing when the slightest change in pressure is detected. Available with PVC or ABS adapters, this Sure-Vent air admittance valve vents up to 160 DFU (branch) or 500 DFU (stack) and fit 3 in. and 4 in. pipes. Oatey products have earned the trust of plumbing professionals for over 100 years. The purpose of an air admittance valve is to provide a method of allowing air to enter the plumbing drainage system without the use of a vent extended to open air and to prevent sewer gases from escaping into a building. An air admittance valve is a one way valve designed to allow air to enter the plumbing drainage system when negative pressures develop in the piping system. The device shall close by gravity and seal the vent terminal at zero differential pressure (no flow conditions) and under positive internal pressures.