With the rapid development of industrial technology, the valve industry put forward more stringent requirements, especially the butterfly valve in the use of low-temperature media, in addition to meet the normal valve performance at room temperature, more importantly, at low temperature The reliability of the lower valve seal, the flexibility of movement and some other special requirements for cryogenic valves. Because the butterfly valve has a compact, small size, light weight (with the same pressure, the same size of the gate valve can be reduced compared to 40% to 50%) fluid resistance, quick opening and closing and a series of advantages, it is widely used. However, some low-temperature installations in our country, such as natural gas liquefaction equipment, air separation equipment and pressure swing adsorption equipment used in the chemical industry, such as valves used in more than 80% of the globe valve or gate valve, the use of a small number of butterfly valves. The main reason is that the sealing performance of the metal sealing butterfly valve is not good at low temperature and other phenomena of internal leakage and leakage of the medium due to the unreasonable structure and other factors seriously affect the safety and normal operation of these low temperature equipments and the low temperature Equipment requirements. According to the continuous development of low-temperature devices in our country, the requirements for cryogenic valves are increasing day by day. Therefore, structural improvements have been made to the metal-sealed butterfly valve and the butterfly valve with high eccentricity and high eccentricity has been developed. No matter whether the medium is hot or cold To meet their needs. Now with its structural features, only a brief introduction of low temperature performance. First, the low temperature valve sealing performance requirements: There are two main reasons for the leakage of low temperature valves, one internal leakage; the second is leakage. 1) The main reason for the internal leakage of the valve is the deformation of the seal pair caused by the low temperature. When the media temperature drops to make the material phase change caused by the volume change, the original grinding precision of the sealing surface warpage caused by low temperature sealing bad. We have DN250 valve low temperature test, the medium is liquid nitrogen (-196 ℃) Butterfly material 1Cr18Ni9Ti (no low temperature treatment) found that the sealing surface warpage deformation of about 0.12mm, which is the main cause of internal leakage. Newly developed butterfly valve from the plane seal to cone seal. The valve seat is an oblique cone oval sealing surface, and the butterfly valve is mounted on the circular seal ring is composed of flexible seal. Seal ring can float radially within the disc groove. When the valve is closed, the elastomeric seal first comes into contact with the minor axis of the elliptical sealing surface. As the valve stem rotates, the sealing ring is pushed inwardly forcing the elastomeric ring into contact with the longer axis of the bevel, eventually causing the elastomeric sealing ring All contact with the elliptical sealing surface. Its sealing is achieved by the elastic ring deformation. Therefore, when the valve body or disc deformation occurs at low temperature, it will be compensated by the elastic sealing ring without leakage and jamming. When the valve is opened, the elastic deformation immediately disappears, basically no relative friction in the opening and closing process, so long service life. 2) valve leakage: First, the valve and the pipe flange connection, due to the connection padding, connecting bolts, and connectors at low temperature shrinkage between the material is not synchronized with the resulting slack and lead to leakage. Therefore, we change the way of connecting the valve body and the pipeline from the flange connection to the welding structure, so as to avoid the low-temperature leakage. The second is the stem and packing leaks. Most of the general valve filling F4, because of its good self-lubricating properties, small friction coefficient (friction coefficient of steel f = 0.05 ~ 0.1), but also has unique chemical stability, it has been widely used. However, F4 also has shortcomings, first, cold tendency; Second, the linear expansion coefficient, resulting in shrinkage at low temperatures lead to leakage, resulting in a lot of ice at the valve stem, so that the valve open failure. Developed for this reason, the use of self-shrinking seal structure of low-temperature butterfly valve that is the use of large expansion coefficient F4 features, through the gap to reach the room temperature, low temperature can be sealed. Second, the valve body, stem bushing design requirements: 1) low temperature valve housing structure and shape. The correct choice of materials on the valve of the normal and reliable work is extremely important. Compared with the stop valve and gate valve, the structure of the butterfly valve not only avoids the deformation caused by the irregular shape and the uneven wall thickness of the shell, but also the shrinkage and temperature difference caused by low temperature stress. Moreover, due to the small size of the butterfly valve, About the shape of the basic is called, so the heat capacity is small; to the cold consumption is also small; shape rules and convenient for the valve cooling measures. For example, newly developed DD363H type disc valve is designed and manufactured according to the particularity of the cryogenic valve in order to ensure the reliable use of the valve under low temperature. For example, 1Cr18Ni9Ti austenitic stainless steel with cubic crystal lattice is selected as the shell material. 2) The choice of stem bushing: According to the user, some low-temperature valves in operation, the valve parts of the sticky, occlusion phenomenon occurs, the main reason is: the matching material selection is not reasonable, to leave the cold clearance is too small , As well as processing accuracy and other reasons. In the development of cryogenic valves, has taken a series of measures to prevent the above phenomenon. For example, we choose the SF-1 composite bearing with small friction coefficient and self-lubricating property on the valve stem upper and lower bushing, which can be suitable for some special needs of cryogenic valve. Metal-sealed butterfly valve has the characteristics of some ordinary valves do not have. In particular, small flow resistance, reliable sealing, quick opening and closing, long service life. The company developed three eccentric metal sealing butterfly valve sealing force from the deformation of the elastic ring to seal, so do not need to use the media force, it can be used for two-way seal. According to some of the characteristics of butterfly valve will be more people attach importance. In the future there will be more butterfly valves used in cryogenic equipment.
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