Forged steel cryogenic shut-off valve for cryogenic liquid storage and transportation equipment management system, with a switch flexible, reliable sealing characteristics can also be used for other low-temperature and cryogenic medium management system. Room temperature valve is the medium temperature -40 ~ +500 degrees, the body of the material is not the same. Low temperature cut-off valve is mainly used in the medium temperature of -196 ~ -150 degrees in the low-temperature liquid medium system shut-off valve. Cryogenic valves, especially cryogenic valves, have very low operating temperatures. In the design of this type of valve, in addition to follow the general design principles of the valve, there are some special requirements. First, the design requirements of cryogenic valves Depending on the conditions of use, the design of cryogenic valves have the following requirements: 1) The valve should have the ability to work long hours in low temperature medium and ambient temperature. 2) Valves should not be a significant source of heat for cryogenic systems. This is because the inflow of heat in addition to reducing thermal efficiency, such as excessive influx, but also the rapid evaporation of the internal fluid, resulting in abnormal pressure, causing danger. 3) Low temperature media should not have a detrimental effect on handwheel handling and packing seal performance. 4) The valve assembly directly in contact with low temperature medium shall have an explosion-proof and fireproof structure. 5) The valve assembly working at low temperature can not be lubricated, so structural measures need to be taken to prevent abrasion of the friction parts. Second, the cryogenic valve material selection 1, the main material of the cryogenic valve (1) the main material selection should be considered from the metallographic considerations, in addition to metal materials with face-centered cubic lattice austenitic steel, copper, aluminum, etc. , The general situation of low temperature brittle steel at low temperatures, thereby reducing the strength and service life of the valve. When choosing the main material, we must first select the material suitable for working at low temperature. Aluminum does not appear low temperature brittleness at low temperature, but due to the hardness of aluminum and aluminum alloy is not high, wear-resistant aluminum surface, scratch resistance is poor, so the use of low-temperature valves have some restrictions, only low pressure and Small diameter valve used. Materials working at low temperature to ensure its low temperature performance, mainly to ensure its impact strength. Trim must be properly selected so that it has sufficient cold impact strength to prevent breakage. The alloy steels c and cr lose their impact strength sooner than -20 ° C, so the service temperature is limited to -30 ° C and -50 ° C, respectively. Nickel steels containing 3.5% ni can be used up to -100 ° C, and nickel steels up to 9% ni can be used up to -192 ° C. Austenitic stainless steel, nickel, Monel, Hastelloy, titanium, aluminum alloys and bronze can be used at lower temperatures (-273 ° C). In addition, the selection of materials for cryogenic valves should also consider the following factors: 1) the minimum service temperature of the valve; 2) the mechanical properties required to maintain the working conditions of the metal material at low temperatures, especially the impact toughness, relative elongation and texture Stability; 3) Good resistance to abrasion at low temperature and without oil lubrication; 4) Good corrosion resistance; 5) Welding properties of materials need to be considered. (2) The choice of material of valve body, valve cover, valve seat and disc (gate) material, the principle of selection of the material of these main body parts is as follows: Ferritic steel is selected when the temperature is higher than -100 ℃; 100 ℃ when the choice of austenitic steel; low-pressure and small-caliber valves can choose copper and aluminum and other materials. Design time according to the lowest temperature to select the appropriate material. (3) the material selection of the stem and fasteners Temperature above -100 ℃, the stem and bolt material ni ,, cr-mo and other alloy steel, the appropriate heat treatment to improve the tensile strength and prevent thread bite Injury and so on. Temperature below -100 ℃, the use of austenitic stainless steel acid-resistant steel. However, 18-8 acid-resistant steel hardness is low, will cause the stem and filler mutual bruise, resulting in filler leakage. Therefore, the stem surface must be hard chromium plating (coating thickness 0.04-0.06mm), or nitriding and nickel-phosphorus treatment to increase the surface hardness. In order to prevent the nut and bolt bite death, the nut is generally used steel or ni ni mo, while the surface coated with molybdenum disulfide. 2, low-temperature valve gasket, filler material selection: With the temperature decreases, a large amount of shrinkage of fluoroplastic, sealing performance will decline, easily lead to leakage. Asbestos filler can not avoid permeability leakage. Rubber liquefied natural gas has swelling, can not be used at low temperatures. Cryogenic valve design, on the one hand by the structural design to ensure that the filler is close to ambient temperature work, for example, the use of long-necked bonnet structure, the packing letter from.