Final answer:
The operator should place the brake valve in a service position, necessarily 'fully applied' to achieve a 15-pound brake pipe reduction, following the specific brake valve manufacturer's guidelines.
Step-by-step explanation:
When operating a train with ME-23 brake valves and aiming to create a 15-pound reduction in the brake pipe pressure, the correct action for the train operator is to keep the brake valve in the fully applied position. ME-23 brake valves are a type of control valve used in train braking systems. To achieve a 15-pound reduction in the brake pipe pressure, the operator activates the brake valve, causing air to escape from the brake pipe until the pressure diminishes by 15 pounds. Holding the brake valve fully applied allows the system to regulate the airflow, facilitating the desired reduction in pressure. This adjustment affects the braking force in the train, ensuring proper control and responsiveness while operating, particularly when managing speed or making stops along the rail route.