Air Governor

The Governor is most often referred to as the D-2 Governor. It is made by Bendix but there are many brand names that make D-2 Governors. The D-2 is very versatile, capable of many different setups with lot of ports / positions/ options. Because of the different setups possible, it is VERY important to match the holes with the old unit or you can create a not operating system.

Air compressors are designed to run whenever the engine is running. As a result, they are able to produce much more air than is needed by the brake system. To prevent the compressor from producing too much compressed air and to reduce the load on the engine, a governor is used in the air brake system. When air pressure is high enough in the system, the governor causes the compressor to stop pumping air (cut-out). When the air pressure drops to a certain point, the governor will cause the compressor to start pumping air again (cut-in). After the air leaves the compressor and goes to the air dryer, then to the wet tank, from this point on you technically have air regulator at various points to further regulate the air to specific pressures.

If you can hear no air leaks with the engine running, and you are not building any air pressure, a VERY high likelihood that it is the governor. This is both an inexpensive and easy to replace part.

If you do not carry a spare governor, get one. They cost less than $20 dollars at most NAPA stores and can prevent you from being stranded on the road.