As the pump pulls water from the pool and pushes through the filter, air can become trapped in the system, causing pressure to build. This high pressure can put a strain on the pump, damaging the mechanism and reducing the effectiveness of the filtering system by lowering flow rates.
Opening the air relief valve releases this pressure. As the excess air is released, the valve will emit a hissing sound. This process is also called “bleeding the filter.”
Made of plastic or brass, the air relief valve is positioned on top of the pool filter tank. When the valve is opened, excess pressure escapes and water flows through the system. When normal pressure is established, the valve can be closed again, restricting the water flow. Pressure above 10 PSI points to pressure build up in a standard-size pool. Pressure varies dependent upon the type of filtration system — cartridge, sand or DE filter.
Air relief valves are usually manually operated. However, on some filtration systems feature automated valves. Typical times to open the air relief valve include: after cleaning out the pump basket, after backwashing, after vacuuming, and when the water level gets below the skimmer.