If the tell-tale knob on an automatic drain valve is extended, the valve is set for which operation?

When the tell-tale knob on an automatic drain valve is extended, it indicates that the valve is set for automatic operation. In this setting, the valve works to automatically release any accumulated moisture or condensation from the air brake system without requiring manual intervention. This feature is crucial in ensuring that the air brake system remains clear of moisture, which can affect performance and safety.

In automatic mode, the drain valve regularly cycles to expel moisture build-up, thereby maintaining the efficiency and reliability of the braking system. This is particularly important in varied operational environments where moisture can easily accumulate. By having the tell-tale knob extended, the operator can visually confirm that the valve is functioning in the automatic mode, offering reassurance that the system will continue to operate effectively. This design helps to simplify maintenance and enhances the safety of train operations.