This section tells you about air brakes. If you want to drive a truck or bus with air brakes, or pull a trailer with air brakes, you need to read this section. If you want to pull a trailer with air brakes, you also need to read Section 6, Combination Vehicles. An air brake endorsement is only required if your vehicle needs a CDL.Air brakes use compressed air to make the brakes work. The Parts of an Air Brake System
There are many parts to an air brake 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
The governor controls when the air compressor will pump air into the air storage tanks. When air tank pressure rises to the "cut-out" 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. The tanks will hold enough air to allow
the brakes to be used several times, even if the compressor stops working. For example, the water can freeze in cold weather and cause brake failure. The water and oil tend to collect in the bottom of the air tank. Be sure that you drain the air tanks completely. Each air tank is equipped with a drain valve in the bottom.
