Air Brakes & Parts

Brakes are the most important safety system in any vehicle. They work by applying friction material mounted on the vehicle, the disc brake pads and brake shoes, to the surfaces of components that rotate with the wheels, the brake rotors and brake drums. When you step on the brake pedal, you apply the force needed to actuate the friction material. On cars and light trucks this force is transmitted by the fluid in a hydraulic brake system. On large heavy-duty trucks compressed air is employed to provide the necessary force. Air brakes are preferred for this application for several reasons.

The basic principle of hydraulic systems is that fluid cannot be compressed, which is why the force applied at the brake pedal also applies the brakes at the wheels. However, vehicles can only carry a finite supply of brake fluid. If a leak develops in the system there will be insufficient pressure to apply the brakes. Although modern hydraulic systems are commonly “split” systems, with each of two sections actuating a set of wheels, if all fluid is lost in one section that portion of the brake system will be inoperable, with severely diminished braking capability.

In contrast, the compressor in an air brake system can provide an unlimited supply of compressed air. And if an air leak does develop and pressure falls below a preset amount, the springs in the brake chambers will automatically apply the brakes and safely stop the truck. Finally, any time a hydraulic brake system is opened for service all air must be bled from the system to ensure the proper hydraulic pressure can be developed. Since trailers are routinely disconnected and connected on semi-trucks, a hydraulic system would be impractical for actuating the trailer brakes. Air brake couplings on the other hand, can easily be detached and attached.

Air brakes are a complicated system which consists of lots of components, including air brake tanks, brake chambers, brake hoses, slack adjusters, dryers, valves, lines, and many other parts. The heart of the system is an air compressor which feeds air through brake pipes into a special tank (or tanks) to be used by the system. Air tanks hold pressurized or compressed air until special valves are applied to release it to engage the brakes. Due to high pressures, these reservoirs must be made from highly durable materials to withstand the forces that act on them. Taking into account that your air brake system may lose its efficiency and even fail in the event of a tank leak, most air tanks are made of high-grade materials to ensure leak-free performance for many years to come.

If you have ever driven a vehicle with air brakes, you know that you must push a special parking brake button before you can drive. The springs in the air brake chambers apply the brakes when the truck is parked and the driver opens the valve, exhausting air pressure from the brake chambers. Pushing the button in applies pressure to the chambers, releasing the parking brakes. In addition, a lot of heavy trucks and commercial vehicles are equipped with an exhaust brake or a “Jake” brake to induce engine braking and help slow the truck without using the service brakes. These are especially helpful to avoid overheating and excessive wear of the service brakes on downgrades.