Which component closes the brake pipe in uncoupled cars?

The correct answer is that the brake pipe is the component that closes in uncoupled cars. In rail transport, the brake pipe is responsible for managing the flow of air to the braking system of a train. When cars are uncoupled, the air supply line—that is, the brake pipe—becomes open to the atmosphere, which causes a drop in air pressure and effectively closes off the braking system of the uncoupled cars. This is a crucial safety feature, as it prevents unintended brake application and ensures that the train operates safely when individual cars are detached.

While other components, such as the brake handle and brake valve, are important in the operation and control of the braking system, they do not specifically close off the brake pipe itself. The brake reservoir stores compressed air for the braking system but does not play a direct role in closing the brake pipe upon uncoupling. Understanding the function of the brake pipe in this context is essential for any train operator, as it directly impacts safety and control when managing train operations.