What feature must the valve have to be used between a boiler and its water column?

The necessity for a valve to be lockable open when used between a boiler and its water column stems from safety and operational protocols in high-pressure piping systems. A lockable open feature ensures that the valve can maintain a constant connection between the boiler and the water column, which is crucial for accurate measurement of water levels and for the proper function of the boiler. This lockable feature prevents accidental closure during operation, which could lead to dangerous conditions such as pressure buildup or improper water levels, potentially causing boiler damage or failure.

This required characteristic is foundational for ensuring that operators can rely on the valve to stay in position, especially in situations where monitoring water levels is critical for safe operation. The focus here is on maintaining process integrity and enhancing safety in high-pressure systems.