What happens to the brake cylinder during the FRA Class II air brake test on PA5?

During the FRA Class II air brake test on PA5, the brake cylinder's pressure is intentionally manipulated to assess the functionality of the air brake system. Specifically, the brake cylinder will move to zero. This allows for a thorough evaluation of the air brake system's ability to release pressure, which is crucial for safety and performance.

Achieving zero pressure ensures that all components of the brake system, such as the release valves and fittings, are functioning correctly and allows for the assessment of any leaks. Identifying leaks or malfunctions during this state is necessary to guarantee the reliability of the braking system before the vehicle operates again.

This test is vital in maintaining safety standards in rail operations and ensuring that any potential issues are rectified before the train is in motion.