1. The materials of compression parts can endure the expansion and shrinkage resulted form the temperature variation of medium, and seal structure is away from permanent deformation under temperature changes. To work under the conditions below -100℃, the parts of valve shall be subject to deep cooling treatment before precision machining. Namely, have the parts cooled in liquid nitrogen box, when the temperature of parts reaches -196℃, keep the temperature for 1～2h, then take them out to have them to the normal temperature naturally, and do in this way twice.

2. Bonnet is extended for the purpose to protect the function of packing box, making packing box somewhat away from low temperature to ensure good seal of packing. Besides, it can be wound with cold insulating materials to prevent loss of cold energy. The length of neck depends on service temperature and the thickness of cold insulating material. When the effect of packing seal turns lower, fill in grease to form up oil seal layer from the middle of packing box, to lower the differntial pressure of packing box and enhance the reliability of seal.

3. To serve a temperature below -100℃, the material of valve stem shall be treated with chromeplating or nitriding to enhance the surface hardness of valve stem and the sealing reliability of packing.

4. Cryogenic ball valve takes a structure to avoid abnormal pressure rise. As the medium in cryogenic valve is gasified and rapidly expanded in volume, the pressure will goes extremely high. When the pressure in the middle cavity of valve rises, the middle cavity and the inlet side can be communicated, or a relief can be mounted at the inlet side of valve, thus to ensure the safe use of valves.

5. The gaskets used on cryogenic ball valves may function reliable seal and restoration under normal and low temperature or under the conditions of temperature changes.