What distinguishes a rising stem valve from a non-rising stem valve?

A rising stem valve is characterized by the visibility of the stem as it moves up or down during the opening and closing process. This feature allows operators to easily see the position of the valve, which provides a clear indication of whether the valve is open or closed based on the stem's height. This visual cue can enhance safety and operational efficiency, especially in situations where it is crucial to monitor the state of the valve quickly.

On the other hand, non-rising stem valves do not display the same visibility since the stem remains mostly hidden within the valve body during operation. This can make it less straightforward to determine the valve's position without additional instruments or indicators.

Overall, the distinguishing factor between these types of valves lies in how the stem is designed to function during operation, with rising stem valves providing a direct visual confirmation of their status.