The valve sealing performance

Valves 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.
Sealing surface material and the processing status of the valve sealing performance of the sealing surface of the valve material and processing conditions have a significant impact leakage. 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.

Properties of the medium on the valve sealing performance of the liquid medium is substantially on the leakage of the viscosity determined by the sealing valve in the same, the various conditions are the same, the viscosity of the medium viscosity smaller than the much smaller leakage medium . Gases and liquids compared to the difference more obvious (except for saturated steam, saturated steam is easy to ensure the sealing surface).

Hydrophilic surface properties of the valve sealing surface of the leak amount of hydrophilic properties due to capillary effect. When the cable zip ties sealing surface as long as a thin film, the need to increase the pressure of the water through the gap. As the metal surface with good hydrophilicity, kerosene can easily penetrate the gap casting and sealing connection. So, in some of the most critical situations, is the use of kerosene for the hydraulic tightness test. Filling the cavities of kerosene tightness test method, equivalent to approximately 0.3? 0.4 MPa pressure tightness test under pressure.

The presence of the sealing film of the valve sealing performance of the sealing film exists between the sealing surface has a significant effect on its sealing performance. When the sealing film on the surface, the destruction of the contact surfaces hydrophilic, so that a larger pressure difference is required to make the medium passes through the pores. In addition, dense sealing film on the surface of the channel to plug the media travel, improve the connection sealing. In the use of film sealing should pay attention: When the work process film is reduced, should be able to recover the oil film thickness. Oils used in the valve being not soluble in the media, nor should evaporate, hardening or other chemical changes.

The closing member of the rigidity and structural features of the valve closure member sealing performance and structure of the rigidity is due to the elasticity of the part. The closed valve closure member is not absolutely rigid, but has a certain flexibility in the pressure of the medium, the size is changing, which force causes the sealing surface interactions. To compensate for these changes on the sealing performance of the closure member, the wire seal sealing surface preferably has a smaller rigidity of the elastic deformation is as large as possible.