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1, Preface? Safety valve is a kind of safety relief device that is widely used in boilers and pressure vessels in petroleum and chemical industries. The spring-type safety valve is one of the more typical one. It is the role of the pressure of the spring pressure load, and by adjusting the size of the spring pressure to adjust the relief valve opening pressure. When the system pressure exceeds the allowable value, it can automatically open and discharge excess system media to the atmosphere or low pressure system, so as to achieve the purpose of pressure relief. When the pressure drops to a certain value, it automatically and quickly shut down to maintain the normal operation of the system. ? 2, the causes of the impact of the safety valve seal? Over the past few years, the author of the safety valve in the use, overhaul and test, concluded that under normal circumstances, the impact of sealing the main reasons are the following:? 2.1, Safety valve closure of the structure? Closure of the structure and type of application of temperature and force. Therefore, when replacing the safety valve closure, do not change the closure type at will. For overhauls where the closures are replaced, the closures should be considered if they have been tested with standard media at ambient temperature and early closure of the closures when installed at the media pressure temperature of the protected system Is it reasonable? In the maintenance methods and media cleanliness, the shut-off pieces of the form of improper, and sometimes after the first take-off seat in the poor seal. 2.2, the closure of the material, hardness and design dimensions impact? In the design of the safety valve, the closure material, sealing surface hardness considerations, maintenance and replacement of closures, should be very careful, shall not be arbitrarily changed. Due to corrosion of the media on the closure, resulting in poor sealing is more common cases. For example, when replacing a methylamine safety valve closure in a urea plant, the seal was badly attacked by methylamine due to the high carbon content in the material despite the selection of high quality stainless steel. When there is no medium pressure in the protection system, the sealing surface of the closing member should bear the pressure generated by the spring. If the sealing surface does not have enough hardness, it will produce large deformation, resulting in poor sealing, brittle material may have sufficient hardness, When the valve is started, the sealing surface may be fragmented due to repeated collision of the sealing surface, which may result in the leakage of the valve. On the other hand, good corrosion resistance of materials, if the surface hardness is poor, in the case of high pressure, can not withstand the mechanical flow on the surface of its mechanical wear and tear can also cause poor sealing. 2.3, the width of the sealing surface and the impact of processing accuracy? In fact, there is a capillary action between the valve disc and the valve seat sealing surface. The width of the sealing surface determines the length of the media path. Thus, as the width of the sealing surface increases, the resistance encountered by the medium in the event of a leak and the consequent blockage of the capillary increases. For this reason, in the maintenance of free to narrow the width of the sealing surface is not appropriate. Under the same conditions, narrowing the width of the sealing surface can reduce the opening pressure of the valve. Although widening the sealing surface can increase the sealing performance, the area of ​​the valve disc subjected to the medium pressure is reduced before the safety valve is closed and opened. This also increases the relief valve opening pressure. When the device is out of service for a long time, due to no medium pressure in the safety valve, the full force of the spring acts on the sealing surface. If the sealing surface is too narrow, the sealing surface may be damaged under larger specific pressure to cause the sealing bad. Experiments show that, in order to reduce the valve flap, valve seat out of each other the possibility of grooves, the flatness of the valve seal, valve seat sealing surface processed into the same width better. The quality of the surface of the sealing surface is good or bad, a direct impact on the closure of sealing. Sealing surface geometry and surface finish and seal has a great relationship. Due to improper processing methods, metal sealing surface in the processing of microscopic uneven and ripples will affect the sealing effect. At present, we used rotary maintenance grinding method, the sealing surface edge depression, poor sealing. 2.4, the impact of assembly quality? After the disassembly of the safety valve reassembly, will also affect the sealing surface quality. Usually due to improper assembly will undermine the closure of the coaxial, so that the sealing surface is not parallel, leading to poor sealing. Valve used for too long, the guide part of the serious wear or replace the valve disc, the guide gap is too large, causing the valve flap in the action of the sealing surface askew. Replace the valve flap, the guide gap is too small, the action of the valve flap jamming, so that the sealing surface can not be properly closed, leading to poor sealing. Due to the deformation of the spring or the wrong assembly position, the spring force distribution unevenly around the sealing surface, resulting in uneven sealing surface pressure, sealing surface partial sealing poor. ? Installation or assembly of the stress will cause deformation of the valve body, so that closure of coaxial changes, sealing line offset, breaking the parallelism of the sealing surface, resulting in poor sealing. Practice has proved that in this case, the wider sealing surface, the smaller the seat diameter, the higher the working pressure, the greater the possibility of damage to the sealing surface. 2.5, the impact of the working medium is protected system? In the case of the same pressure, temperature, viscous medium than viscous medium leakage is small. Liquid media are easier to seal than gaseous media. So take into account the allowable medium for valve design. Medium temperature will cause thermal deformation of the sealing surface, the sealing material will cause thermal gradient, causing the sealing surface warpage. Therefore, the safety valve at room temperature medium, the sealing test results are good, and installed in high temperature medium equipment, the sealing is poor. To this end, after the repair of the safety valve seal test, to take into account the working temperature of the medium. The life of the sealing surface is also related to the stability of the medium pressure. If the pressure fluctuates too much, it will cause frequent relief of the safety valve so that the sealing surface will be damaged in a short period of time. 3 Conclusion In summary, leading to spring-loaded safety valve sealing a lot of bad factors, and the relationship between these factors is also very complicated, in order to ensure the safety valve seal in good condition, to protect the security of the system you need Design, installation, use, maintenance, calibration and other personnel in all aspects of careful and meticulous work. More Keyword Search: Safety Valve