www.risleyhomeinspections.com Air admittance valves (AAV's) are mechanical plumbing devices that can take the place of plumbing vents. How does it work? Air admittance valves work with a sealing mechanism that is lifted to let air into the drain system when there is negative pressure and allow proper drainage. Positive pressure causes the mechanism to close so that gases cannot escape into the home. #AirAdmittanceValves are very inexpensive and easy alternative to installing