How do you engage the parking brake in an air brake system?

Engaging the parking brake in an air brake system is done by pulling the parking brake control knob. This knob is specifically designed for the purpose of activating the parking brake, which applies the brakes and holds the vehicle in place when parked.

Using the parking brake is essential, especially for heavy vehicles, as it prevents them from rolling when stationary. The mechanism works by releasing air from the brake chambers, allowing the brake shoes to make contact with the drums, thereby securing the vehicle.

Other methods listed do not correctly engage the parking brake. For instance, pressing the brake pedal is related to the service brakes used during driving, not for parking. Turning off the ignition does not engage the parking brake; instead, it merely powers down the vehicle. Releasing the service brakes also does not activate the parking brake; in fact, it serves the opposite function. Thus, pulling the parking brake control knob is the only correct and effective method to engage the parking brake in an air brake system.