Application of metal hard sealing butterfly valve in low temperature equipment

With the rapid advancement of industrial technology, the valve industry is facing increasingly strict requirements, especially for butterfly valves used in cryogenic environments. These valves must not only meet general performance standards but also ensure reliable sealing at low temperatures, maintain smooth operation, and fulfill other specific demands unique to cryogenic applications. As industries continue to evolve, the need for high-performance cryogenic valves has become more critical than ever. Butterfly valves are known for their compact design, lightweight construction, and ease of operation, making them ideal for various applications. However, despite these advantages, they are still underutilized in cryogenic systems. In China, for instance, over 80% of valves used in facilities like Tianhuo liquefaction units, air separation systems, and pressure swing adsorption equipment are gate or globe valves, with very few butterfly valves in use. This is mainly due to the poor sealing performance of metal-seated butterfly valves at low temperatures, which can lead to internal leakage and structural issues, compromising the safety and efficiency of the equipment. To address this challenge, continuous improvements have been made in the design of metal-seated butterfly valves. A new type of high-eccentric, pure metal-sealed butterfly valve has been developed, featuring a national patent. This valve is suitable for both high and low-temperature environments and offers excellent sealing performance. Below, we provide a brief overview of its low-temperature capabilities. First, the sealing requirements for low-temperature butterfly valves: There are two main causes of leakage in cryogenic valves: internal and external leakage. 1) Internal leakage is primarily caused by the deformation of the sealing surfaces at low temperatures. When the medium cools and undergoes a phase change, the material may contract or expand, causing warping of the highly polished sealing surfaces. For example, during a low-temperature test on a DN250 valve using liquid nitrogen (-196°C), the 1Cr18Ni9Ti butterfly plate showed a deformation of about 0.12mm, leading to significant internal leakage. The newly developed butterfly valve uses a conical elliptical sealing surface instead of a flat one. The valve seat features an oblique conical shape, while the disc is equipped with a floating elastic sealing ring. When the valve closes, the ring first contacts the short axis of the elliptical surface and then gradually moves inward, ensuring full contact with the long axis. This design allows the elastic ring to compensate for any thermal deformation, preventing leakage and jamming. During opening, the seal returns to its original shape without friction, significantly extending the valve's service life. 2) External leakage often occurs at flange connections and the stem packing. At low temperatures, gaskets and bolts can contract, loosening the connection and causing leaks. To solve this, the new valve uses a welded structure instead of flanged connections, eliminating the risk of low-temperature leakage. Additionally, traditional PTFE (F4) packing, while widely used for its low friction and chemical resistance, tends to shrink at low temperatures, leading to leakage. The new cryogenic butterfly valve incorporates a self-shrinking sealing design that accounts for this expansion, ensuring consistent performance across temperature ranges. High-performance butterfly valves, ball valves, and hard-seal butterfly valves are now available to meet the growing demand for reliable cryogenic solutions in industrial applications.

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