Air relief valve is made of plastic or brass. It is placed on the top of the pool filter tank, and is referred to as the pressure-relief valve. It helps to relieve pressure that builds up inside the filter. It is operated manually. It is intended to measure the amount of materials flowing through a system or a part of a system. The air-relief valve is an integral part of a pools pumping and filtration system. As the pools pump sucks out water from the pool, it is forced through a filter. This water is then forced through the air-relief valve.