Which procedure ensures proper seating of the valve when closing?

The process of closing a valve, then opening it a half turn before closing it again, is known to help ensure that the valve seats properly. This procedure allows the valve disc to settle into the seat more evenly, reducing the chance of any debris or misalignment affecting the valve's ability to create a seal when it is fully closed.

This technique also helps to alleviate any potential binding that may occur as the valve is being closed, which can be caused by thermal expansion or misalignment. By reopening it slightly, there is an opportunity for the valve to realign itself with the seat, thus ensuring a more effective seal upon the final closure.

Other methods, while they may provide a certain degree of closure, might not guarantee that the valve has seated correctly. For example, setting up tight using a valve wrench or tightening by hand focuses on force rather than on the necessary alignment for proper sealing. Closing against a stop and inserting a locking pin adds security but does not address the alignment concerns. Hence, opting to slightly open the valve prior to a final shut is the procedure that effectively achieves proper seating.