Any valve used as a shut-off to a water column must be sealed how?

The correct choice indicates that a valve used as a shut-off to a water column must be sealed open and locked. This is essential because the water column is critical for the accurate measurement of water levels in a boiler. If the valve were sealed shut, it would prevent water from flowing to the sight glass or water column, making it impossible to monitor the water level effectively.

Sealing the valve in the open position ensures that there is a continual and unobstructed flow of water for proper gauge function, thereby enhancing boiler safety and operation. Locking the valve in the open position also prevents accidental closure, which could lead to unsafe operating conditions.

Maintaining this configuration allows operators to ensure that the water level is accurately monitored and maintained, thus safeguarding against low water conditions that can lead to boiler damage or failure.