PURPOSE: To prevent damage by inserting hard sleeve and insert rings of tungsten carbide into sheet rings mounted to a movable gate valve chest in a state of compression preload.

CONSTITUTION: A hard sleeve 44 of tungsten carbide is inserted into an opening 42 of a gate 32 positioned in a valve chest 18 in a movable manner in a state of compression preload. Then, hard insert rings 46 and 48 of tungsten carbide are inserted into sheet rings 34 and 36 fitted to recesses 38 and 40 in the valve chest 18 in a state of compression preload. During the closing movement of the gate 32, a wire 50 is sheared off into two parts on the hard insert rings 46 and 48 by operation with the hard sleeve 44. By the constitution, damage can be prevented.