Air Admittance Valves come in a variety of different sizes to fit most applications. The valves are designed to allow the free entry of air into the sanitary pipework system without the escape of foul gasses into the building. When installed into sanitary pipework systems, the Air Admittance Valve not only prevents the loss of water from trap seals due to induced siphonage, but also has the added advantage of providing an early warning indicator to a potential drainage blockage.