This product controls pressure in your air system. When your systems air pressure reaches your governor's cut-out pressure, then the spring in the governor will become depressed and will let air pass through the unloader ports and to the compressor activating the compressors unloader mechanism which will stop sending air to your reservoir air tanks (the compressor will continue to run). Once your air systems pressure drops and reachers your cut-in pressure, the spring in governor will "spring back" and deactivate the unloader mechanism causing air to go back to air tanks and to pressurize your system. Governor is used in all the major truck manufacturers including Peterbilt, Kenworth, Volvo, International and Freightliner. Cross References 284358, 284358R, 102178, 102178X, 108818, 227435, 275491, 275491X, 275707, 275707X, 18537, KN18500X, KN18530, KN18537, VHD18537