Application of metal sealing butterfly valve in cr

2022-08-08
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With the rapid development of industrial technology, more stringent requirements have been put forward for the valve industry. Especially for the butterfly valve used in low-temperature medium, in addition to meeting the performance of general valves, the more important thing is the reliability of valve sealing under low temperature, the flexibility of action and some other special requirements for low-temperature valves. With the rapid development of industrial technology, more stringent requirements have been put forward for the valve industry, especially for the butterfly valve used in low-temperature medium. In addition to meeting the performance of general valves, the more important thing is the reliability of valve sealing under low temperature, the flexibility of action and some other special requirements for low-temperature valves

as we all know, butterfly valves have a series of advantages, such as compact structure, small volume, light weight (40% ~ 50% less than gate valves with the same pressure and the same diameter), low fluid resistance, rapid opening and closing, etc. However, more than 80% of the valves used in some low-temperature devices in China, such as natural combustion liquefaction equipment, air separation equipment and pressure swing adsorption equipment, are globe valves or gate valves, and the number of butterfly valves is very small. It is analyzed that the main reasons are the poor sealing performance of the metal sealing butterfly valve under low temperature, and the internal and external leakage of media caused by other unreasonable structures, which seriously affect the safety and normal operation of these low-temperature equipment and cannot meet the requirements of low-temperature equipment

according to the continuous development of low-temperature devices in China, the requirements for low-temperature valves are increasing day by day. In order to meet the needs of the development of market economy, the structure of metal sealing butterfly valve is improved, and a three eccentric pure metal butterfly valve with high sealing performance is developed (Figure 1, which has been applied for national patent). Whether the medium is high temperature or low temperature, it can meet its needs. In combination with its structural characteristics, the low temperature performance is briefly introduced

I. requirements for sealing performance of low-temperature butterfly valve:

there are two main reasons for leakage of low-temperature valve: one is internal leakage; Second, external leakage

1) the internal leakage of the valve is mainly caused by the deformation of the sealing pair at low temperature. When the temperature of the medium drops to the point where the material changes phase, the volume changes and the sealing surface with high grinding accuracy warps, resulting in poor low-temperature sealing. We conducted a low-temperature test on DN250 valve. The medium was liquid nitrogen (-196, which can be said to be during microcomputer operation). The butterfly plate material was 1Cr18Ni9Ti (without low-temperature treatment). It was found that the warpage deformation of the sealing surface was about 0.12mm, which was the main cause of internal leakage

the newly developed butterfly valve is changed from plane seal to conical seal. The valve seat is an inclined conical elliptical sealing surface, which forms a sealing pair with a positive circular elastic sealing ring embedded on the butterfly plate. The sealing ring can float in the inner diameter of the butterfly plate groove. When the valve is closed, the elastic sealing ring first contacts with the short shaft of the elliptical sealing surface. With the rotation of the valve rod, the sealing ring is gradually pushed inward, forcing the elastic ring to contact with the long shaft of the inclined conical surface. In the electronic information and electrical industry, the elastic sealing ring finally contacts with the elliptical sealing surface. Its sealing is achieved by deformation of the elastic ring. Therefore, when the valve body or butterfly plate is deformed at low temperature, it will be absorbed and compensated by the elastic sealing ring, and there will be no leakage and jamming. When the valve is opened, the elastic deformation disappears immediately, and there is basically no relative friction during the opening and closing process, so the service life is long

2) external leakage of the valve: first, when the valve and the pipeline are connected by flange, the leakage is caused by the relaxation caused by the unsynchronized shrinkage of the connecting gasket, connecting bolt and connecting piece under low temperature. Therefore, we changed the connection mode of valve body and pipeline from flange connection to welding structure to avoid low-temperature leakage. The second is the leakage at the valve rod and packing. Generally, F4 is used as the packing of most valves because of its good self sliding performance, small friction coefficient (friction coefficient f=0.05 ~ 0.1 for steel) and unique chemical stability, so it is widely used. However, F4 also has some shortcomings. First, it has a large tendency of cold flow; Second, the coefficient of linear expansion is large, resulting in cold shrinkage at low temperature, leading to leakage, resulting in a large number of ice at the valve stem, so that the valve fails to open. For this reason, the developed low-temperature butterfly valve adopts a self shrinking sealing structure, that is, it can be sealed at room temperature and low temperature through the reserved gap by taking advantage of the large expansion coefficient of F4

II. Design requirements for valve body and valve stem bushing:

1) the computer software of low temperature valve shall be upgraded for free throughout its life; Door shell structure shape. Whether the material selection is correct or not is of great significance to the normal and reliable operation of the valve. Compared with the stop valve and gate valve, the structural characteristics of the butterfly valve not only avoid the deformation caused by irregular shape, uneven shell wall thickness, cold shrinkage at low temperature and temperature difference stress, but also because the butterfly valve is small, the shape of the valve body is basically symmetrical, so the heat capacity is small; The consumption of precooling capacity is also small; The registration time of shape products is too long, and the shape rule is convenient for the cold insulation measures of valves. For example, the newly developed dd363h butterfly valve is designed and manufactured in full accordance with the particularity of the low temperature valve to ensure the reliable use of the valve at low temperature. For example, the shell material is 1Cr18Ni9Ti austenitic stainless steel with cubic lattice, etc

2) selection of valve stem bushing: according to the user's feedback, some low-temperature valves are in operation, and the rotating parts of the valves are sticky and occluded from time to time. The main reasons are: the selection of matching materials is unreasonable, the reserved cold clearance is too small, and the machining accuracy. A series of measures were taken to prevent the above phenomena during the development of low-temperature valves. For example, SF-1 composite bearing with small friction coefficient and self-lubricating performance is selected for the upper and lower shaft liners of the valve rod, which can be applied to some special needs of low-temperature valves

metal seal butterfly valve has the characteristics that some ordinary valves do not have. Especially, it has small flow resistance, reliable sealing, rapid opening and closing, long service life, etc. The sealing force of the three eccentric metal sealing butterfly valve developed by our company comes from the deformation of the elastic ring, so it does not need the help of the medium force, so it can be used for two-way sealing. According to some characteristics of butterfly valve, it will be valued by more people. In the future, more butterfly valves will be applied to cryogenic equipment

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