What is the function of a 'check valve' in the air brake system?

The function of a 'check valve' in the air brake system is to prevent backflow of air. This is crucial for maintaining the integrity and effectiveness of the braking system, as it ensures that air pressure is directed appropriately throughout the system while also preventing any potential loss of air that could compromise braking efficiency.

When the air brake system is activated, compressed air is applied to the brake cylinders, creating the necessary force to engage the brakes. A check valve allows this air to flow in one direction—towards the brake cylinders—while blocking any air that attempts to flow back into the supply line from the brakes. This functionality is vital for ensuring that the brakes remain effective and responsive when engaged, thereby enhancing safety and performance during train operations.

The other options do not accurately describe the primary role of a check valve, as it is not designed to measure performance, enable faster braking times, or release pressure during maintenance. Its essential purpose is solely related to preventing backflow, which supports overall system reliability.