How do air brakes work in a heavy truck?

Air brakes in heavy trucks operate through the use of compressed air, which is fundamental to their function. When the driver presses the brake pedal, air is released from the storage tanks and directed to the brake chambers. Inside these chambers, the compressed air forces a diaphragm to move, which then pushes a rod that engages the brake shoes against the brake drum or disc. This mechanical action creates friction, slowing down or stopping the vehicle.

The use of compressed air is particularly advantageous in large vehicles because it allows for a reliable and consistent braking force that can handle the significant weight and momentum of heavy trucks. The air brake system is designed to be fail-safe; if there is a loss of air pressure, the brakes automatically engage, ensuring that the truck can stop safely.

Other options describe different braking systems that are not applicable to air brakes. For example, hydraulic systems rely on fluid pressure and are common in lighter vehicles, while electronic signals govern braking in modern systems but do not represent air brake operation. Vacuum systems, on the other hand, are typically found in older braking technologies and are not used in heavy trucks, as they cannot generate the necessary force for such large vehicles. Thus, the correct answer accurately reflects the functioning principle behind air brakes.