The Principle Operation of an Atmospheric Vacuum Breaker Backflow Prevention Device – Air Inlet Valve and Drainage

The AVB shall be installed only where water will not cause damage to the area where the AVB is installed. Typically, on startup, the AVB float disc will close the air inlet port preventing the discharge of water out of the air inlet port. The AVB is designed to prevent spilling under all rates of flow. However, in some cases the air inlet will not close before water discharges out of the air inlet port. Therefore, the AVB shall be installed where the occasional discharge of water from the air inlet port in not an issue. Siphon conditions and pressure surges due to opening and closing of the inlet valve may cause the APVB to discharge water out of the air inlet port. If the float disc does not seal the air inlet port closed because of dirt or debris located between the float disc and air inlet port water will discharge from the AVB may occur. Although the AVB is designed to prevent spillage of water, the AVB should not be installed in concealed locations or areas where water leakage caused by ware of the internal parts could cause water damage to the surround area. If the AVB must be installed in an area where water spillage could cause damage, proper drainage shall be provided. The AVB must be installed so that the air inlet valve operates in the vertical position to prevent water discharge. If the AVB is not installed according to manufacturer’s specification, it may malfunction and not operate properly.