Screwed connection valve:
This kind of connection is usually carried out by processing the
valve inlet and outlet into taper or straight pipe thread so as to connect it to the tapered pipe thread or pipeline. However, this connection may lead to large channel leakage, so you have to use sealants, sealing adhesive tapes or fillers to plug the channel. If the difference of expansion parameter is too large or the range of working temperature is too big, thread junction must be sealing welded despite the fact that the material of the body can be welded. Screwed connection valve is mainly taken to mean a valve whose nominal diameter is less than 50mm. It will be very difficult for the junction to be installed and sealed if the nominal diameter is oversized.
In order to facilitate the installation and disassembly of screwed connection valve, pipe joints can be used on piping system at an appropriate location. Pipe sockets can also be used as pipe joints if the nominal diameter of a valve is less than 50mm. What’s more, thread of pipe sockets combines these two parts together.
Flange connection valve:
It is more convenient to install and disassemble flange connection
valve. But compared with screwed connection valve, it is more heavy and expensive. Flange connection valve applies to pipe connection with all sizes and classes. However, when the temperate exceeds 350 degrees, bolt, gasket and flange will become slack and lower the load of bolt lower. Therefore, leakage problem may be occurred on flange connection.
Welding connection valve:
Compared with flange connection, this connection is more reliable in hard situation, because it can apply to all kinds of pressure and temperature. However, it is difficult to disassemble and reinstall the welding connection valve. For this reason, this kind of valve can work reliably for a long period, even in hard using condition and high temperature situation, such as coal-fired power plant, nuclear engineering and ethylene project.
Welding type valve, whose nominal diameter is less then 50mm, often uses socket to carry the pipe. Because there is a gap between welding socket and pipe and it can be corroded by some medium. Also, the vibration of pipe can make the connection part slack. Combined these two factors, the application of socket weld shall have certain limitations.
If the nominal diameter is big, the using condition is hard, or the working temperature is high, groove welding will be often used for the body. Therefore, this work should be done by highly skillful welder.
