What component controls the flow of air into and out of the reservoirs on each freight car?

The control valve is the critical component responsible for managing the flow of air into and out of the reservoirs on each freight car. This valve regulates the pressure of the air within the braking system, allowing for smooth operation during braking and releasing of the brakes. It ensures that the correct amount of air is supplied to the air brake system, which is essential for the effective functioning of the brakes.

When the train engineer applies the brakes, the control valve responds by allowing air to escape from the reservoirs to the brake cylinders, activating the braking mechanism. Conversely, when the brakes are released, the control valve allows air to refill the reservoirs to maintain proper pressure. This operation is vital to ensure the safety and efficiency of the train's braking system.

Other components listed, such as the compressor, air reservoir, and brake cylinder, play significant roles in the overall braking system, but it is specifically the control valve that directly manages the intake and exhaust of air within the reservoirs.