Studor Air Admittance Valves may be used as an option to open pipe vents in drainage, waste and vent systems. The devices are designed to open and admit fresh air when negative pressures occur from fixture discharge. Instantly, this equalizes the pressure within the system, and as a result, trap seals are protected. Once this equalization is complete, the valve seals tight by gravity, preventing any transmission of foul air through the device. The Mini-Vent fits 1 1/2" and 2" pipe sizes, and the Maxi-Vent fits 3" and 4" pipes. Studor, Inc.