Oatey Sure-Vent 39018 Air Admittance Valve

This valve’s sweet spot technology opens at -0.01 psi and seals at 0 psi and above, screening on air inlets to guard the seal. This one-way valve is designed to allow air to enter the plumbing drainage system when negative pressures develop in the piping system. This device shall close by gravity and seal the vent terminal at zero differential pressure (no flow conditions) and under positive internal pressures.