(1) threaded connection valves
This connection is usually through to turn the valve inlet and outlet can be connected to the taper pipe nipple or pipe taper or straight thread, because of this connection may appear larger leakage passage, sealants, sealing adhesive tape or filler can be used for blocking the channel, if the valve body material can be welded, but expansion coefficient difference is very big, or working temperature range is larger, threaded connections must use honey, threaded valve is the valve nominal diameter less than 50 mm, if the diameter is too large, the installation of the connecting parts and seal is very difficult, for the convenience of installation and removal of threaded valve, in proper position of piping systems are pipe fittings, nominal diameter of less than 50 mm valve can through joint connection, nipple thread connect the two parts together,
(2) the flange valve
Convenient installation and disassembly, but they are more heavy than threaded valve, more expensive, therefore, it is suitable for all kinds of diameter and pressure pipe connection, but, when the temperature exceeds 350 degree, because of the bolts, gaskets and flange become loose, also greatly reduces the load of bolts, exert vigorously may produce leakage on flange connection,
(3) the welding connection valve
This connection applies to all the pressure and temperature, the more load conditions when using more reliable than the flange connection, it is difficult to remove and reinstall but welding valve, so that they can use was limited to reliable operation for a long time, or in the case of a force and high temperature, such as thermal power plant, nuclear power projects, the ethylene projects such as pipelines, 50 mm below the nominal diameter welding valve usually have a sleeve, is used to load the flat end bearing pipe, socket welding because the gap between the socket and the pipe is formed in the socket welding process, the gap may be some kind of medium corrosion, the vibration of the pipeline can lead to joint fatigue, so the application of the socket is restricted, the nominal diameter is big, high temperature, working condition of the bad situation, the body usually USES the groove welding, for in situ welding seam,