The purpose of these devices is to supply potable water without danger of damage to the device due to freezing; and to provide protection of the potable water supply from contamination due to back siphonage or back pressure less than or equal to 3 meters (10 feet) of head pressure. This standard covers design and performance requirements for water supply system wall hydrant devices. These devices shall have a permanent means including air inlet valve(s) to prevent backflow from a potential health hazard due to back siphonage, and back pressure less than 3 meters (10 feet) of head pressure. The device shall only be used on systems where the only source of back pressure comes from an elevated hose equal to or less than 3 meters (10 feet) in height and from full rated supply pressure. The devices shall be classified as follows: (a) Type A: These hydrants automatically drain the water when the water supply is shut off and the hose removed to prevent damage from freezing; (b) Type B: These hydrants automatically drain the water with a hose removed or attached, end nozzle closed, and the hydrant valve closed; and (c) Type C: Same as Type A. Backflow prevention is achieved by alternate principle of holding pressure versus relieving pressure.