What happens to an air brake system when the driver releases the brake pedal?

In an air brake system, when the driver releases the brake pedal, the associated control valve is activated to decrease air pressure in the brake chambers. This reduction in air pressure is crucial because it allows the spring mechanisms within the brake chambers to push the brake shoes away from the drums or discs, consequently releasing the brakes.

The air brake system operates on a principle where pressurized air is used to apply the brakes; releasing the brake pedal removes that pressure, enabling the springs to retract the brake components. This process ensures that the vehicle can move freely without unnecessary drag from the brakes, thereby improving safety and driving efficiency. Understanding this mechanism is essential for drivers operating vehicles with air brake systems, as it directly influences how braking and release functions are performed.