Weak current College】 【resolution sealing performance and quality of the valve --- Power By】 【China power house network.

<br> Valve sealing performance is good and bad quality check valve of one of the main index. Valve sealing performance mainly includes two aspects, namely the internal leakage and leakage. Internal leakage is the seat and shut down parts of the media to reach between .sealed, examination of standards for two in our country. One is a Board member of December 1992, 1993, 1 June started implementing national standards GB/T13927-92 "universal valve pressure test". This standard is the reference to the use of international .standards ISO5208-1982 the industrial valves valve pressure test of the developed; the other is the original Ministry of machine-JB/T9092 publication-1999 valve test and inspection of this standard is the reference to API598-1986 the valve of checking and testing " .. <br> <br> GB/T13927-92 apply to general industrial valve of checking; JB/T9092-1999 applies to the inspection of oil industrial valves. Leakage refers to stem packing location of leaks, in flange gasket parts of leakage and .the valve because of the casting defect caused by leakage, leakage is not allowed. If the media is not allowed to be discharged into the atmosphere, the leakage of seal sealing than internal leakage. Therefore, the valve sealing performance should cause the importance attached by .the manufacturer. Affect the valve sealing performance factors mainly: <br> <br> ① sealed surface quality. <br> <br> ② seal width; <br> <br> ③ valve and the valve after pressure difference; <br> .<br> ④ sealed surface materials and their processing status; <br> <br> ⑤ media properties; <br> <br> ⑥ hydrophilic surface; <br> <br> ⑦ existence of seal oil film; <br> <br .> ⑧ off pieces of rigid and structural characteristics. <br> <br> Seal the surface quality on the valve sealing performance of the valve seat sealing surface refers to pieces with close contact to close to each other. When sealing surface pressure in 40MPa following ., sealing the surface quality on the valve sealing performance plays a decisive role. This is because when the seal surface pressure is small, low surface roughness, the leakage rate increased rapidly. When sealing surface pressure, surface roughness on the effect of significantly reducing leakage .. <br> <br> Seal width on the valve sealing performance of sealing the surface width determines the length of the pores. When you increase the width, fluid motion along the pores, lengthened stroke movement resistance increase. Increase the width of the sealing .surface reduces the high pressure valve of erosion and wear. Seal width increase, causing leakage stroke length proportional to increase, allowing you to scale to reduce leakage. But seal width increase, in the same seal strength, sealing pressure decrease, makes the possibility of .leakage. Therefore, you cannot increase the sealing surface of infinite width. <br> <br> Valve and the valve after pressure difference on the valve sealing performance of theoretical analysis, valve, the valve after pressure difference and leakage is proportional to the relationship .. But the test proves: in other things equal, the leakage rate of growth is more than the increase of the pressure differential. Leakage and pressure difference between can approximate the following type: <br> <br> G = M (P2 + SN .△ △ P) type: M, N, S - constant coefficient △ P - - differential pressure, these coefficients depend on the material, the surface quality of machined seals, sealing surface pressure and other conditions; <br> <br> Seal the .surface materials and their processing status on the valve sealing performance of sealing surface materials and their processing status on valve leakage has a great effect. Due to the sealing surface of the remaining gap size depends on the sealing surface micro-unevenness, so, if you .are using steel materials for sealing ring, causing the same seal level, there must be greater than the pressure, its value must exceed the brass sculpture of sealing ring pressure value. And seal the surface treatment, such as the crest of the deformation, dimensions ., and sealing gap of change and other phenomena have occurred in the metal surface layer, it is clear that the performance and substrate surface materials performance distinct. Changes caused by processing can affect surface thickness 50 μ m. Grind, do not expose the base metal .. Work surface organization different from the metal matrix organization. Materials performance and geometric shapes and compared to the micro-geometry. Metal performance differences, usually less than other factors. Sealing surface in low voltage conditions, this situation is even more pronounced. When the .pressure is higher than 40mpa, surface roughness on the sealing performance of just reduce the influence of the material will increase. <br> <br> Media properties on the valve sealing performance of liquid media influence on leakage is basically determined by the viscosity in the .same sealed valve, all kinds of things equal, viscosity big medium small than the viscosity of medium leakage are much smaller. Gas medium and liquid media difference compared to the more obvious (saturated steam, vapor easily guarantee seal). <br> <br .> Surface hydrophilic on valve sealing performance of hydrophilicity impact leakage because of the role of the pores. When the seal on the surface, as long as there is a layer is a thin oil film, will be increased through the gap of water pressure. Due .to the metal surface with good hydrophilicity, kerosene can easily permeable casting and seal attached clearance. Therefore, in some of the most crucial occasions, is the use of kerosene for the sealing of the hydraulic test. Using cavity filling kerosene to tightness test, approx .. 0.3 ~ 0.4MPa pressure pressure tightness test. <br> <br> Seal oil film on the valve sealing performance of sealing surfaces present seal oil film on the sealing effect significantly. When the surface is sealed oil film, destroyed the contact surface between .hydrophilic, which requires a large pressure difference to the media through the pores. In addition, there are dense surface sealing oil film can jam media channel to improve your connection. In the use of oil-film sealed attention: when work processes to reduce oil .film, you should be able to recover oil film thickness. Valve in the grease is not allowed to dissolve in media, nor should it evaporates, hardening or other chemical change. <br> <br> Turn off pieces of rigidity and structural features of .the valve sealing performance of closed parts of rigidAnd structure is due to the flexibility of the parts. Because of the closed valve closes the pieces do not absolutely rigid, but have a certain flexibility, and media-related pressure, size change, this is also .caused by the interaction of the sealing surface of the force. To compensate for these changes on close of sealing performance, the best is to seal the surface has less rigid elastic deformation, which is as large as possible. At valve production enterprises attach importance to .affect the valve sealing performance factors, the valve sealing performance caused by leakage minimized to stop valve of the leak and leakage. <br>.