Highcraft Air Admittance Valves are the Ideal Venting Solution for a Variety of Commercial and Residential Applications. The Advanced 360° Air Flow Patented Venting Technology is Designed to Allow Air Flow into DWV Systems While Preventing Unpleasant Odors and Sewer Gases from Escaping into Building. When Negative Pressure is Created in the System, the Resulting Suction Power Raises the Membrane in the Valve and Thus Admits Air into The System. The Valve Then Promptly Closes as the Membrane Falls, Preventing the Diffusion of Odors. It is Super Handy in Remote Applications, as it Eliminates the Need for Multiple Roof Penetrations or Accessing Stack Vent Directly. Manufactured with the Highest Quality Materials and Workmanship, It will Serve Your Plumbing Needs Faithfully.