Which valves are used in the correct sequence on a feed-water line?

The correct sequence of valves on a feed-water line is significant for the proper operation and safety of the system. In the context of the provided question, the sequence of a stop valve, followed by a pump, and an automatic valve is crucial for several reasons.

The stop valve is typically used to control the flow of water into the system. It can isolate sections for maintenance or during system shutdowns, providing a necessary safety measure. Placing the pump after the stop valve ensures that the pump can operate without the risk of backflow when maintenance is needed.

Following the pump with an automatic valve is practical because this type of valve can regulate flow without requiring manual intervention, often responding to changes in pressure or system demands. This arrangement ensures that water is delivered efficiently while maintaining system integrity and functionality.

Overall, this combination allows for effective control and management of the feed-water system, facilitating maintenance while ensuring that water flow is managed appropriately according to demand. The other sequences provided in the options do not follow the standard operational practices observed in feed-water systems, whereas the identified sequence provides a logical and efficient flow of control.