What is the purpose of the cut-out cock in the air brake system?

The cut-out cock serves a critical role in the air brake system by allowing for the isolation of a specific car's brake system from the overall train's air brake system. This is particularly important when maintenance or repairs need to be performed on individual cars without affecting the entire train's braking capability. By closing the cut-out cock on an isolated car, the air brake system of that car can be disengaged, ensuring that the brakes are not engaged while the rest of the train can continue to operate safely.

This functionality is essential for operational flexibility and safety, as it enables train crews to manage each car's braking system effectively. The ability to isolate a car can prevent undue wear or damage to the brakes of that car and avoids unnecessary complications during train operations. Other options, while pertaining to different aspects of air brake systems, do not capture the specific and operationally significant role of the cut-out cock.