Applies to devices classified as atmospheric type vacuum breakers that are single pipe-applied (does not apply to tank ball cocks or similar devices that depend on float operated valves to control flow). The purpose of these devices is to provide protection of the potable water supply against pollutants or contaminants that enter the system due to backsiphonage through the outlet. Under backsiphonage conditions, a small amount of water is permitted to exit through the air ports. The device shall: 1) Be installed downstream of the last control valve; 2) Not be subjected to backpressure 3) Not be subjected to more than twelve (12) hours of continuous water pressure; and 4) Be installed with its critical level (CL) not less than 150 mm (6 inches) above the flood lever rim of the fixture or appliances served; or deck mounted/equipment mounted atmospheric vacuum breakers shall be installed in accordance with the manufacturer's instructions, with its critical level (CL) not less than 25 mm (1 inch) above the flood level rim of the fixture or appliance served.