Union Pacific Air Brakes Practice Test

The proper procedure for cutting out the control valves on a defective car involves closing the branch pipe cutout cock first. This step is essential because it isolates the defective control valve from the rest of the air brake system. By doing so, you prevent any air from entering or exiting through the defective valve, ensuring that the rest of the braking system remains functional and safe to operate. Closing the cutout cock effectively secures the system, allowing you to proceed with further necessary steps, such as releasing air pressure or inspecting components, without risking any unintended release of air pressure or interference from the defective part. This procedure is crucial for maintaining the safety and reliability of the braking system during maintenance or repairs.