About the technical department's analysis of titanium valve leakage
Date:2022.07.10 Views:832
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1. External leakage of the valve: First, when the valve and the pipeline are flanged, the leakage occurs due to the asynchronous shrinkage of the connecting gasket, the connecting bolt, and the looseness between the materials of the connecting piece at low temperature. Therefore, we changed the connection method between the valve body and the pipeline from the flange connection to the welded structure to avoid low temperature leakage. The second is the leakage at the valve stem and packing. Generally, F4 is used for packing of most valves, because of its good self-slip performance, small friction coefficient (f = 0.05 to 0.1 for steel), and unique chemical stability, so it is widely used. However, F4 also has its shortcomings. First, the tendency of cold flow is large; second, the coefficient of linear expansion is large, which leads to leakage due to cold shrinkage at low temperature, resulting in a large amount of icing at the valve stem, so that the valve fails to open. The low-temperature butterfly valve developed for this purpose adopts the self-shrinking sealing structure, that is, the feature of the large expansion coefficient of F4 is used, and the purpose of sealing at normal temperature and low temperature is achieved through the reserved gap.
2. The valve has internal leakage; the main reason is that the sealing pair is deformed at low temperature. When the temperature of the medium drops to the point where the material undergoes a phase change, the volume changes, and the sealing surface with high grinding precision is warped and deformed, resulting in poor low-temperature sealing. We have carried out low temperature test on DN250 valve, the medium is liquid nitrogen (-196 ℃), the disc material is 1Cr18Ni9Ti (without low temperature treatment), and it is found that the warpage deformation of the sealing surface is about 0.12mm, which is the main cause of internal leakage.
The newly developed butterfly valve is changed from a flat seal to a conical seal. The valve seat is an oblique conical elliptical sealing surface, which forms a sealing pair with a circular elastic sealing ring embedded in the butterfly plate. The sealing ring can float radially in the disc groove. When the valve is closed, the elastic sealing ring first comes into contact with the short axis of the elliptical sealing surface, and gradually pushes the sealing ring inward with the rotation of the valve stem, forcing the elastic ring to contact the long axis of the inclined conical surface again, eventually leading to the elastic sealing ring Make full contact with the oval sealing surface. Its sealing is achieved by the deformation of the elastic ring. Therefore, when the valve body or disc is deformed at low temperature, it will be absorbed and compensated by the elastic sealing ring, and there will be no leakage and jamming. When the valve is opened, the elastic deformation disappears immediately, and there is basically no relative friction during the opening and closing process, so the service life is long.
