The structure and size of the valve's end connection are critical to the installation and use of the valve. Improper selection may result in mismatched dimensions or connection structures during installation, leading to installation difficulties. Therefore, special attention should be paid when selecting a valve to ensure the correct and suitable connection end face structure is chosen, thus ensuring smooth installation of the valve.
Valve end face connection forms are generally divided into three types: welded end connections, threaded end connections, and flanged end connections, with flanged end connections being the most commonly used structure.
1. Flange Connection Structure
2. Threaded Connection
Threaded connections are detachable connections and are commonly used in situations where welding is not suitable or disassembly is required. Threaded connections are divided into internal and external threaded connections. Internal threaded connections usually have valve body ends machined into tapered or straight tube female threads, which are connected to pipes that are machined with tapered or straight tube male threads. External threaded connections have valve body ends machined with male threads for easy installation and removal of threaded-end valves. Compared with welding connections, valves with threaded connections have lower strength but stronger sealing. Therefore, when applied in petrochemical plants, they are often subject to the following conditions:
Mostly used in pipelines with DN ≤ 40;
Threaded connections of pipe fittings should use taper thread;
Valves with threaded connections should not be used for managing highly toxic media;
Valves with threaded connections are not recommended for temperature operating conditions above 200℃ and below -45℃;
Valves with threaded connections are not recommended for parts that may experience stress corrosion, clearance corrosion, or variable loads due to vibration, pressure pulsation, and temperature changes;
When valves with threaded connections are used on pipelines carrying flammable gases, seal welding is recommended for sealing.