Introduction to General Equipment Valve Types

    (1) Threaded Connection Valves

    These valves feature tapered or straight pipe threads at inlet/outlet ends for connection to piping. Due to potential leakage paths, sealants, PTFE tape, or packing are often required. If the valve body is weldable but has a significantly different thermal expansion coefficient from the pipe, or if operating temperatures fluctuate widely, the threaded joint should be seal-welded. Threaded valves are typically used for nominal diameters ≤ DN50; larger sizes pose installation and sealing challenges.

    Pipe unions or nipples can be installed nearby to facilitate assembly and disassembly.

    (2) Flanged Connection Valves

    Flanged valves offer convenient installation and removal but are heavier and more expensive than threaded types. Suitable for all sizes and pressure ratings. However, above 350°C, bolt relaxation and gasket creep can reduce clamping force, potentially causing leaks in high-stress joints.

    (3) Welded Connection Valves

    Welded connections provide superior reliability under extreme pressure and temperature conditions, outperforming flanges in severe service. However, they are difficult to disassemble, making them ideal for permanent installations in critical systems like power plants, nuclear facilities, and ethylene plants.

    Small welded valves (≤ DN50) often use socket-weld ends. However, the gap between pipe and socket can trap corrosive media and induce fatigue from vibration—limiting their use.

    For large-diameter or high-severity applications, butt-weld ends are preferred. Such welds require strict quality control and skilled welders to ensure integrity.

(Source: Mechanical Experts Network)