The Principle Operation of an Atmospheric Vacuum Breaker Backflow Prevention Device – Installation Considerations

The AVB must be installed a minimum of 6 inches above the highest usage point in the system. This requirement prevents the possibility of head pressure in the piping system creating a backpressure condition. The AVB shall be installed vertically and plumb. There shall be no shut-off valves downstream of the AVB that would otherwise keep the AVB under constant pressure. The AVB shall not be subjected to more than twelve hours of continues pressure or flow due to the possibility of the disc float becoming permanently attached to the air inlet port making the AVB inoperative. The AVB inlet supply should be shut-off periodically if the intent of the AVB is to be used continuously. The AVB shall be installed according to manufactures and industry standards. The AVB shall not be installed where backpressure conditions may develop. The AVB can be used for low flow installations. The AVB shall only be installed above grade where flooding is not an issue. Installing an AVBs in a pit or vault is not acceptable since a underground vault could be subjected to flooding and the groundwater could be drawn into the water system during a backsiphonage condition. The AVB works on atmospheric principles and cannot be installed in an enclosure where the atmosphere cannot enter the air inlet port or in an area where air contaminants could be drawn into the air inlet port and into the potable piping system during a backsiphonage situation. The air inlet port should never be blocked with such items as rags, insulation, mops or other cleaning equipment. The air inlet port shall be kept clean at all times and free of foreign material. The AVB should be installed where limited spillage is not an issue or objectionable.