What position must retaining valves remain in?

The retaining valves must remain in the closed position to ensure the proper function of the air brake system. In this position, the valves effectively retain air pressure in the brake cylinders, which is crucial for maintaining braking effectiveness when needed. The design of the retaining valves allows for the prevention of air loss that would otherwise reduce braking power, especially in long or heavy trains.

When the valves are closed, they prevent the escape of compressed air, allowing the train to maintain a reliable braking force. This is particularly important during emergency braking situations where maximizing brake pressure is essential for stopping the train safely and efficiently.

In contrast, if the retaining valves were in the exhaust position, air would be allowed to escape, which could lead to a loss of braking capability. An open position would not be appropriate for the intended function of these valves, just as a neutral position would not serve to secure air pressure in the brake system. Understanding the required position of retaining valves is crucial for effectively managing the operation of air brakes.