5.1 – The Parts of an Air Brake System There are many parts to an air brake system. You should know about the parts discussed here. 5.1.1 – Air Compressor The air compressor pumps air into the air storage tanks (reservoirs. The air compressor is connected to the engine through gears or a v-belt. The compressor maybe air cooled or maybe cooled by the engine cooling system. It may have its own oil supply or be lubricated by engine oil. If the compressor has its own oil supply, check the oil level before driving. 5.1.2 – Air Compressor Governor The governor controls when the air compressor will pump air into the air storage tanks. When air tank pressure rises to the "cutout" level (around 125 pounds per-square-inch or "psi, the governor stops the compressor from pumping air. When the tank pressure falls to the "cut-in" pressure (around 100 psi, the governor allows the compressor to start pumping again.