Factors affecting the performance of the valve seal

Assessment of the valve is the valve sealing performance merits of the main indicators of quality . Valve sealing performance mainly include two aspects, namely, leakage and leakage . Endoleak refers to the closure member between the valve seat and sealing of the media reach , assessment criteria within the country there are two missing . One is the State Technical Supervision Bureau released in December 1992 , June 1, 1993 began the implementation of a national standard GB/T13927-1992 " universal valve pressure test ." This standard is used with reference to the international standard ISO5208-1982 " industrial valves valve pressure test " developed ; another was issued by the Ministry of Machinery Industry JB/T9092-1999 " valve testing and inspection ," This standard is referenced API598- 1986 " valve inspection and test " developed . GB/T13927-1992 for general industrial valves inspection ; JB/T9092-1999 industrial valves for the oil inspection . Leakage refers to the parts of the stem packing leak , the leak in the flange gasket and valve parts casting defects caused due to leakage, leakage is simply not allowed. If the media is not allowed into the atmosphere , then the leakage of seal leakage than the inner seal more important. Therefore, the valve sealing performance should lead to the manufacturer 's attention.
Factors affecting the performance of the main valve seal are: ① sealing surface quality ; ② sealing surface width ;plastic padlock security seals ③ valve before and after the valve pressure difference ; ④ sealing surface material and its processing status ; ⑤ media properties ; ⑥ surface hydrophilicity ; ⑦ seal film presence ; ⑧ closed parts of rigidity and structural characteristics .
⑴ quality sealing surface of the valve sealing performance of the sealing surface of the valve seat and the closure member is in contact with each other to shut down part. When the sealing surface pressure at 40MPa or less, the quality of the sealing surface of the valve sealing performance play a decisive role . This is because : When the sealing surface pressure is small, low surface roughness , the leakage is increasing rapidly . When the sealing surface pressure is large, the surface roughness on the leakage has been significantly reduced .
⑵ width on the valve sealing surface of the sealing performance of the sealing surface width determines the length of the pores . When the width is increased, fluid movement along the pores stroke lengthened to increase the resistance movement . Can be reduced to increase the width of the sealing surface pressure in the valve erosive wear . Increase the width of the sealing surface , it will cause leakage increased in proportion to the stroke length , and thus be able to proportionately reduce leakage. But the sealing surface width increases , in the same sealing force , vehicle seals the sealing pressure than decreases, but also make the possibility of leakage increases. Therefore, the increase can not be unlimited sealing surface width.
⑶ valve before and after the valve differential pressure on the valve sealing performance is analyzed theoretically , valves before and after the valve pressure difference is proportional to both the amount of leakage . But tests proved : in other conditions are the same , the leakage volume growth is increasing pressure differential over . Leakage between the pressure difference can be approximated by the following formula : G = M (N △ P2 + S △ P) where : M, N, S - constant coefficients, which depend on the material , the sealing surface processing quality , the sealing surface pressure and other conditions ; △ P - pressure differential.
⑷ sealing surface materials and their processing status on the valve sealing performance of the sealing surface materials and their processing status of the valve leakage have a great impact . As the remaining gap between the seal faces depends on the sealing surface micro-roughness , so that , if the use of steel materials, seals, resulting in sealing of the same , there must be greater than the pressure , the value must exceed brass system value than the pressure seal . The sealing surface of the processing state , such as a peak distortion , and sealing the gap size changes and other phenomena occur on the metal surface , it is clear that the performance of the surface properties of the base material have significant difference . Induced changes in the machining surface can affect the thickness of 50μm. Grinding the base metal is not exposed . Work is different from the metal surface tissue matrix organization . Geometry and material properties and microstructure geometry compared to little effect . Differences in the performance of metal , usually less than other factors . Sealing surface when working under low pressure conditions , the situation is more prominent. When the pressure ratio is higher than 40MPa , the surface roughness of the sealing performance is reduced , and the impact of the material is increased.