How does the parking brake function in an air brake system?

The parking brake in an air brake system operates by utilizing springs to apply the brake when air pressure is released. This is a critical safety feature in vehicles equipped with air brakes, as it ensures that the brakes will engage automatically if there is a loss of air pressure. When the air pressure in the system drops below a certain threshold, or when the driver manually activates the parking brake, the springs are activated, forcing the brake shoes against the brake drum. This design is particularly effective in preventing the vehicle from rolling when parked, especially on inclines.

This method of operation contrasts with hydraulic systems, which rely on fluid pressure, or electric systems, which depend on motors to apply brakes. By using a spring mechanism, the air brake system guarantees a reliable and fail-safe method of securing the vehicle when not in operation.