BEIER control valves for cryogenic service, can get over the leakage, main two condition of leakage: inner leakage and external leakage.
The reason of valve’s inner leakage is that the seal pair have deformation in low temperature service. When the temperature of media falled to make material changed, and it’s changed in volume ,the seal surface have warpage from original high precision grinding, then that’s the case of sealing badness in low temperature. We once carried on the cold temperature test to the DN250 valve, the medium for the fluid nitrogen (-196 ℃) the butterfly disc material were 1Cr18Ni9Ti (after low-temperature treatment) had not discovered the packing surface warp distortion quantity reached about 0.12mm, this was the main reason to created inner leakage.
The new designed butterfly valve have been changed from plane seal to conical surface seal. seat ring have a oblique cone oval sealing surface, with the circular resilient sealing ring wedged above the valve disc composed seal pair. sealing ring can be floated in groove of disc. as valve shutdown, resilient sealing ring contacted with minor axis of elliptical sealing surface. Along with turn of stem, progressive pulled sealing ring entad, made resilient sealing ring contacted with major axis of oblique cone oval sealing surface, finally made resilient sealing ring full contacted with elliptical sealing surface. The sealing is depended on the deformation of resilient sealing ring. Thereby as it's happened of body and disc deforming in low temperature. the deformation will be absorbed and compensated, It's haven't happened that case of leaking and over tightening. as valve is open, the resilient deformation will disappeared, and as in the shutdown process basically havn't relative friction, it’s the cause valve have a long service term.
The external leakage of valve: one of the cause is flanged type body connection, as a result of it’s connection bolt, connection parking and connector is loose to be leaking in low temperature services. therefore we changed the body connection type from flanged to welding connection, to avoid leakage in low temperature services. the second cause is the leakage between stem with packing part. commonly the packing of most valve is F4,cause the self-slipping stability, little friction coefficient, and special chemical stability, so have a wide appliance. but the shortage of F4 is that: great inclination of cold flow, high linear expansion coefficient, bringing shrinkage in low temperature result in leakage, made mass of freeze on the stem part, result in turning on valve unsuccessful, and our control valve for cryogenic service have self-shrinking sealing structure, using F4 high expansion coefficient point, by the remaining clearance to reach the sealing purpose in high-and-low temperature services. |
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