"Air-Valves are widely used in clear water Pipe Lines to evacuate the accumulated air under pressure, for exhaust of air when such pipes are filled with water & for ventilating air into the pipes when they are being emptied of water. They help in reducing the risk of pipe bursting due to water hammer. Air-Valves should be used according to the size & pressure of the pipe line. The different types of air valves are Small Orifice Single Air Valve, Small Orifice Double Air Valve, Double Air Valve with Screw Down Isolating Valve and Double Air Valve Mounted on Horizontal Isolating Sluice Valve."