What is the purpose of applying the brakes from added cars after they have been connected to a train?

Applying the brakes from added cars after connecting them to a train serves primarily to verify that the angle cocks are open throughout the entire train. When angle cocks are open, it allows for proper air flow through the brake lines, which is essential for the train's braking system to function effectively. By applying the brakes, the train operator can confirm that the brakes are responsive and ensure that there is continuity of the compressed air necessary for brake operation.

Additionally, this action helps to identify whether there are any issues with the connection between cars, ensuring that all cars are properly integrated into the train's braking system. This testing is crucial for maintaining safety, as improper or closed angle cocks could lead to ineffective braking and potential accidents. Thus, ensuring the openness of angle cocks through this procedure is a fundamental practice for train operators.