An air admittance valve is a pressure-activated, one-way mechanical vent that is used in a plumbing system so that roof penetrations and conventional types of pipe venting are no longer needed. When wastewater is discharged, the valve opens and allows air to enter the pipe for efficient drainage.
When there is no wastewater discharge, the air admittance valve remains closed and prevents sewer gas from escaping. Some advantages of using air admittance valves include the reduction of the venting materials required in a plumbing system and an increase in the efficiency of plumbing labor. Moreover, using an air admittance valve allows flexibility in terms of the layout of plumbing fixtures and can reduce the maintenance problems related to conventional vents.