Fits 2, 3/75mm or 4/110mm pipe. Dual fit synthetic rubber finger seal outlet. Also incorporates 2 Universal outlet. A1 rated. Air flow capacity of 16.3 l/s. The valve diaphragm lifts and allows air to be drawn into the system when it is subjected to negative pressure. On cessation of negative pressure the diaphragm returns to the closed position thereby preventing the escape of foul air into the building.