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SECTION 5 AIR BRAKES This Section Covers: • The Parts of an Air Brake System • Dual Air Brake • Inspecting Air Brake Systems • Using Air Brakes If you want to drive a truck or with air brakes or pull a trailer with air brakes, you need to study this section. If you want to pull a trailer with air brakes, you also need to study Section 6, Combination Vehicles. Air brakes use air to make the brakes work. Air brakes are a good and safe way of stopping and vehicles, but the brakes must be well maintained and used properly. Air brakes are really three different braking systems: brake, brake and brake. • The brake system applies and releases the brakes when you use the brake pedal during normal driving. • The brake system applies and releases the parking brakes when you use the parking brake control. • The brake system uses parts of the service and parking brake systems to stop the vehicle in a brake system failure. The parts of these systems are discussed in greater detail below.
There are many parts to an air brake system. You should know about the parts discussed here.
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 may be air cooled or may be 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 driving.
The governor controls when the air compressor will pump air into the storage tanks. When air tank pressure rises to the “cut-out” level (around pounds per-square-inch or “psi”), the governor the compressor from pumping air. When the tank pressure falls to the “cut-in” pressure (around psi), the governor allows the compressor to start pumping again.
Air storage tanks are used to hold compressed air. The number and size of air tanks varies among vehicles. The tanks will hold enough air to allow the brakes to be used several times, even if the stops working.
Compressed air usually has some water and compressor oil in it, which is bad for the air brake system. For example, the water can freeze in cold weather and cause failure. The water and oil tend to collect in the bottom of the air tank. Be sure that you the air tanks completely. Each air tank is equipped with a drain valve in the bottom. There are two types: 1. Manually operated. By turning a turn or by pulling a cable. You must the tanks yourself at the of each of driving. (See Figure 5.1.) Figure 5.1 72
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