What method can you use to test that spring brakes activate automatically?

The method of fanning off the air pressure by applying brake pressure is effective for testing that spring brakes activate automatically. When you fan off the air pressure, you reduce the air supply to a point where the service brakes can no longer hold the vehicle, which should trigger the spring brakes to engage. This process demonstrates that the automatic activation of spring brakes properly occurs when the air pressure drops to the set threshold.

The other options may relate to the general maintenance and operation of air brake systems, but they do not directly test the functionality of the spring brakes under conditions that accurately simulate a loss of air pressure. Monitoring air pressure while driving may give a continuous reading of the system's pressure but does not demonstrate the activation of spring brakes. Checking for leaks in the air lines is important for ensuring system integrity but does not validate the automatic engagement of the spring brakes. Inspecting the spring brake mechanism visually can help ensure components are intact but does not provide a functional test of the brakes' activation in real time.