Butterfly valves are widely used due to their advantages, including compact structure, small size, light weight (40%–50% lighter than gate valves of the same pressure and diameter), low fluid resistance, and rapid opening and closing.

Leakage in cryogenic valves mainly occurs in two ways: internal leakage and external leakage.

1. Internal leakage is primarily caused by deformation of the sealing surface at low temperatures. When the medium temperature drops to a point where the material undergoes a phase change, volume changes occur, causing the originally highly precision-ground sealing surface to warp and deform, resulting in poor low-temperature sealing.

*The newly developed butterfly valve has changed from a planar seal to a conical seal. The valve seat is an oblique conical elliptical sealing surface, which, together with a perfectly circular elastic sealing ring embedded in the butterfly plate, forms a sealing pair.

*The sealing ring can float radially within the butterfly plate groove. When the valve is closed, the elastic sealing ring first contacts the short axis of the elliptical sealing surface. As the valve stem rotates, it gradually pushes the sealing ring inward, forcing it to then contact the long axis of the oblique conical surface, resulting in complete contact between the elastic sealing ring and the elliptical sealing surface. Its sealing is achieved through the deformation of the elastic ring.

*Therefore, when the valve body or butterfly plate deforms at low temperatures, the elastic sealing ring absorbs and compensates for the deformation, preventing leakage and jamming. This elastic deformation disappears immediately when the valve is opened, resulting in virtually no relative friction during opening and closing, thus extending its service life.

2. External leakage of valves: Firstly, when the valve and pipeline are connected by flanges, leakage can occur due to the asynchronous contraction of the connecting gaskets, bolts, and fittings at low temperatures, leading to loosening. Therefore, we changed the valve body connection to a welded structure to avoid low-temperature leakage. Secondly, there is leakage at the valve stem and packing.

Generally, most valves use F4 packing because of its good self-lubricating properties, low coefficient of friction (f=0.05～0.1 for steel), and unique chemical stability, making it widely used. However, F4 also has drawbacks. Firstly, it has a strong tendency to flow cold; secondly, its high coefficient of linear expansion causes contraction at low temperatures, leading to leakage and extensive icing on the valve stem, ultimately causing valve malfunction. To address this, a cryogenic butterfly valve was developed that employs a self-sealing structure, utilizing the high coefficient of expansion of F4 to achieve a seal at both room and low temperatures through a pre-existing gap.

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