What are the requirements of national standards regarding the installation of gate valve stem nuts?

National Standard GB/T 12234, “Steel Gate Valves with Bolted Covers for the Oil and Gas Industry”, stipulates that the valve stem nut shall be installed from the top of the bracket, and the upper part of the gate valve stem nut shall be a polygonal cylinder with a keyway or a structure of equivalent strength connected to the handwheel. When the valve is open, the handwheel shall be removable without causing the valve stem and gate to drop to the closed position. If a threaded bearing gland is used, it shall be secured by spot welding or other methods.