Analysis of Sealing Problems in High-Temperature Butterfly Valves

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　The sealing performance of a valve refers to the ability of its sealing pair to prevent the leakage of the medium, and it is an important technical performance indicator for valves. The sealing pairs of butterfly valves are constantly evolving. Double-eccentric butterfly valves achieve sealing by utilizing the force exerted by the valve stem between the valve seat and the butterfly plate, which induces a certain degree of elastic deformation in the sealing pairs. There are two sealing surfaces: one is a conical sealing surface and the other is a circular sealing surface; therefore, double eccentricity results in a linear seal. 　　The triple-eccentric butterfly valve is developed on the basis of the double-eccentric butterfly valve; with the center of the double-eccentric valve stem as the pivot point, the conical sealing surface is deflected by a certain angle. As a result, the sealing surface of the triple-eccentric butterfly valve is no longer a circular linear seal but rather an elliptical surface seal, giving it an asymmetrical shape. To prevent the butterfly valve from closing too tightly, the sealing surface of its disc portion is parallel to the valve flow channel; thus, the triple-eccentric butterfly valve fundamentally changes the design structure of conventional butterfly valves. 　　When the butterfly valve is closed, the sealing of the disc portion of the triple-eccentric butterfly valve is achieved through the specific pressure of the valve stem. Around the elliptical frustum-shaped butterfly disc of the three-eccentric butterfly valve, there is a sealing ring made by stacking stainless steel plates and flexible graphite together. This type of sealing combines the advantages of both metallic hard sealing and non-metallic soft sealing, resulting in high sealing performance. When butterfly valves operate under conditions of extremely high or low temperatures, temperature changes can cause the sealing elements to deform. If this deformation is not effectively controlled and compensated for, gaps will appear in the sealing pair, leading to leaks. Therefore, under normal conditions, butterfly valves are not suitable for use in ultra-high or ultra-low temperature environments. 　　To expand the application range of butterfly valves, efforts are made starting from the design of their sealing structure; by using elastic sealing pairs or enhancing the ability of these sealing pairs to deform elastically, the deformations that occur between the valve’s sealing pairs due to temperature changes can be compensated for, thereby ensuring reliable sealing of the butterfly valve under ultra-high temperature conditions.