What is a necessary action before brakes can engage in an air brake system?

In an air brake system, compressing the air is essential before the brakes can engage. The air brake system operates by using compressed air to force the brake shoes against the brake drums, which slows down or stops the vehicle. Without the air being compressed and stored in the air tanks, there would be insufficient pressure to activate the brake chambers.

This compressed air is crucial because it is the primary mechanism that allows the brakes to function. The system relies on air pressure to release or apply the brakes effectively, highlighting the importance of the air compression process in ensuring safe braking performance.

Other actions, such as starting the engine or switching on headlights, do not impact the functionality of the air brake system directly. While depressing the parking brake is part of the braking process, the brakes cannot engage without the initial step of air compression. Thus, ensuring that the air is compressed is a critical step in the overall operation of air brakes.