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(1) Threaded connection valves: This type of connection is usually achieved by machining the inlet and outlet ends of the valve to have tapered or straight pipe threads that can be connected to tapered tube thread fittings or pipes. Since such connections can have large leakage paths, sealant, sealing tape, or packing can be used to block these paths. If the valve body material is weldable but has a large difference in expansion coefficient, or if the operating temperature range is wide, gland sealing must be used for the threaded connection. Valves with threaded connections are those with a nominal diameter of less than 50 millimeters. If the diameter is too large, it becomes difficult to install and seal the connecting components. To facilitate the installation and removal of threaded valves, pipe fittings are available at appropriate locations in the piping system. Valves with a nominal diameter of less than 50 millimeters can be connected using sleeve joints, the threads of which join the two components together. (2) Flanged valves are easy to install and remove. But they are bulkier and more expensive than threaded valves. Therefore, it is suitable for pipe connections of various diameters and pressures. However, when the temperature exceeds 350 degrees, the bolts, gaskets, and flanges become loose, which **reduces the load on the bolts; applying excessive force to the flange connection can cause leakage. (3) Welded connection valves – This type of connection is suitable for all pressures and temperatures, and it is more reliable than flange connections when used under various loading conditions. However, welded valves are difficult to disassemble and reinstall, so their use is limited to situations where they can operate reliably for long periods of time, or under stress and high temperatures. Such as thermal power plants, nuclear power projects, ethylene plant pipelines, etc. Welded valves with a nominal diameter of 50 millimeters or less usually have a welding sleeve to support the pipe at the loaded end face. Plug welding is limited in its use because the gap between the plug and the pipe is formed during the welding process, and this gap can be corroded by certain substances; moreover, vibrations of the pipe may cause fatigue in the joint. In situations with large nominal diameters, high temperatures, and harsh operating conditions, the valve body is usually welded using grooved welding, requiring the welds to be formed in situ.