The compressed air braking system is a type of friction brake for large vehicles, railroad cars, and other vehicles that carry heavy loads. Air brakes use compressed air that presses on a piston and then applies pressure to the brake pad to stop the vehicle. Air brakes use a pneumatic system or air rams rather than a hydraulic system.
Why Use Air Brakes for Heavier Vehicles?
Motor cars and smaller vehicles use a hydraulic system for its brakes. Compared to a heavier vehicle’s air rams or pneumatic valves in its air brakes, hydraulic brakes occupy less space and have fewer components in lighter vehicles.
Since trucks and busses are heavy, they require a large force to stop. With a hydraulic system, the driver has to exert more effort on the brake pedal to stop the truck or bus, which is next to impossible. Even with a brake booster, it will still be hard to push the pedal connected to the master cylinder or pneumatic valve and then to the callipers and brake disk.
Air brakes use compressed air because of its high potential energy. The compressed air keeps the engaging brakes open. When the driver steps on the brake, it is actually reducing the air pressure from the brakes, thus engaging the callipers again. Therefore, it doesn’t require much effort from the driver to step on the brake pedal.
Naturally, air brake systems are more expensive than ordinary hydraulic disk brake systems. This is because air brakes are more complicated, contains more components, and requires many processes when in use.
Who Invented the Air Brake?
The pneumatic air-brake system, sometimes called the triple-valve air brake system, was invented by George Westinghouse, an engineer. He realised the importance of safety in the new railroad industry at that time and designed the system to be used for railroad cars. Air brakes are a triple-valve system because:
- The brake must be charged – the system must be filled with pressurised air before the brakes will release. When a rail car or vehicle is stopped, the brakes remain engaged. To free the brakes so the vehicle can move, the system must be filled or pressurised again.
- As the brake is applied – the air pressure decreases. As this happens, the valve allows air back into the air tanks, while the brakes move to the applied position.
- After releasing – once the air escapes after breaking, the increased pressure releases the brakes.
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