The Replacement Air Valve is for use with all 4” and 6” Clear View Filters. This Kit contains one Air Valve Fitting and one Cap. Air valves do not need to be replaced very often and rarely go bad. This is the Valve where air is applied to empty the oil out of See Through Filter Assemblies. When a small shot of air is applied to the filter assemblies the oil pump gears on the inlet side restricts oil from going back through the inlet line. The oil is pushed out the outlet side into the motor basically pre oiling the engine. The system can not be over pressurized no mater how long air is held on. Can also use a hand bicycle pump to empty filter assembly.