Valve sealing performance is one of the main indicators of the quality of the valve test. Valve sealing performance mainly includes two aspects, namely, internal leakage and leakage. Internal leakage refers to the seal between the valve seat and the closure of the medium to achieve the level of leakage assessment standards in our country there are two. One is the national standard GB / T13927-1992 "General Valve Pressure Test" issued by the State Bureau of Technical Supervision in December 1992 and implemented on June 1, 1993. This standard is based on the use of international standards ISO5208-1982 "industrial valve pressure test" developed; the other is the original Ministry of Machinery Industry released JB / T9092-1999 "valve test and inspection", the standard is to reference API598- 1986 "valve inspection and test" formulated. GB / T13927-1992 For general industrial valve inspection; JB / T9092-1999 for the oil industry with the valve test. Leakage refers to the leakage of the stem packing, leakage in the flange gasket area and leakage of the valve body due to casting defects, and leakage is not allowed at all. If the medium is not allowed to vent to the atmosphere, the leak seal is more important than the leak seal. Therefore, the valve sealing performance should be caused by the manufacturer's attention. The main factors that affect the sealing performance of the valve are: ①the quality of the sealing surface; ② the width of the sealing surface; ③ the pressure difference before and after the valve; ④ the sealing surface material and its processing state; ⑤ the nature of the medium; ⑥ surface hydrophilicity; The existence of film; ⑧ close the rigidity and structural features. ⑴ sealing surface quality of the valve sealing performance of the valve sealing surface refers to the valve seat and closing parts contact with each other to close the part. When the pressure on the sealing surface below 40MPa, the sealing surface of the quality of the valve sealing performance plays a decisive role. This is because when the pressure on the sealing surface is small and the surface roughness is low, the amount of leakage rapidly increases. When the specific pressure on the sealing surface is large, the effect of surface roughness on leakage is significantly reduced. ⑵ sealing surface width of the valve sealing performance of the width of the sealing surface determines the length of the capillary. When the width increases, the flow of fluid along the capillary stroke longer, increased resistance to movement. Increasing the width of the seal faces can reduce erosion wear in high pressure valves. Increasing the width of the sealing surface can cause the length of the leakage stroke to increase in proportion to the amount of leakage that can be proportionally reduced. However, the width of the sealing surface increases. Under the same sealing force, the sealing pressure is reduced, which in turn increases the possibility of leakage. Therefore, the sealing surface width can not be infinitely increased. ⑶ valve pressure difference between the front and the valve sealing performance of the valve From the theoretical analysis, the valve before the valve after the pressure difference and the leakage is proportional to both. However, tests show that, under the same conditions, the increase of leakage exceeds the increase of pressure difference. The relationship between leakage and pressure difference can be approximated by: G = M (NΔP2 + SΔP) where: M, N, S - constant coefficients, which depend on the material, the sealing surface Processing quality, pressure on the sealing surface and other conditions; △ P - pressure. ⑷ sealing surface material and its processing status of the valve sealing performance of the sealing surface material and its treatment of the valve leakage has a significant impact. Since the size of the remaining gap between the sealing surfaces depends on the microscopic unevenness of the sealing surface, it is necessary to have a larger specific pressure if using a sealing ring made of a steel material, resulting in the same degree of sealing, The system of seals than the pressure value. Seal-related surface treatment conditions, such as crest deformation, size and seal gap changes, and other phenomena occur on the metal surface, it is clear that the performance of the surface and the substrate material performance are significantly different. The variation caused by the machining can affect the surface layer thickness of 50 μm. When grinding, the base metal is not exposed. The work surface organization is different from the metal matrix organization. Material properties and geometry and micro-geometry compared to little effect. The differences in metal properties are usually less than those of other factors. This situation is even more noticeable when the sealing surface is operated under low pressure. When the specific pressure is higher than 40MPa, the influence of the surface roughness on the sealing performance is reduced, and the influence of the material is increased. ⑸ media properties of the valve sealing performance of the liquid medium on the impact of leakage is basically determined by the viscosity of the same valve in a sealed valve, under the same conditions, the viscosity of the medium than the viscosity of small medium leakage is small many. Differences between gas and liquid media are more obvious (except for saturated steam, saturated steam is easy to ensure sealing surface). ⑹ surface hydrophilic properties of the valve sealing surface hydrophilic affect the amount of leakage is due to the role of capillary properties. When the sealing surface as long as there is a thin layer of oil film, you need to increase the pressure of water through the gap. Due to the good hydrophilicity of the metal surface, kerosene can easily penetrate the gap between the casting and the seal. Therefore, in some of the most critical occasions, is the use of kerosene for sealing hydraulic test. The use of kerosene cavity filling method for sealing test, equivalent to about 0.3 ~ 0.4MPa pressure seal test. ⑺ the presence of seal oil film on the valve sealing performance Sealing surface between the sealing film has a significant impact on its sealing. When there is a sealing film on the surface, the hydrophilicity between the contact surfaces is broken, which requires a large pressure difference to allow the medium to pass through the pores. In addition, the surface of a thick seal oil film can block the channel of the media to improve the connection of sealing. When using the oil film seal should pay attention to: When the film is reduced during operation, should be able to restore the thickness of the film. The grease used in the valve is not allowed to dissolve in the medium nor should it evaporate, harden or have other chemical changes.刚 Close the rigidity and structural characteristics of the valve on the sealing performance of the closure of the rigidity and structure of the impact is due to the elastic parts. Since the closing piece of the closed-circuit valve is not absolutely rigid, but rather has a certain elasticity, the dimensions vary with the medium-related pressure, which also causes a change in the interaction of the sealing surface forces. In order to compensate for the effect of these changes on the sealing performance of the closing element, it is advisable to make the sealing surface less rigid, that is to say to as large an elastic deformation as possible. Hope the valve manufacturers to pay attention to the factors that affect the valve sealing performance, valve leakage caused by sealing performance to minimize the leakage to prevent leakage and leakage of the valve.