Three Different End Connections for Valves

Today here we will introduce three popular end connections for valves. There are respectively the flanged, threaded and welded end connections, which are utilized to connect the pipelines.

The first type is called flanged end connection, valves joined by which can be installed and disassembled relatively easily, but the disadvantage of it is heaver in weight and more expensive in price, comparing with valves connected by another type called threaded end connection we will mention next. The flange end connection have been popularly utilized to connect various pipes in different pressure and size, since not so much tightening torques are required for connection, also compared with the threaded end connection. Another disadvantage of flange end connection is its leakage when the temperature reach 350°C, the flange connection has to bear the very big pressure when the bolt, filer piece and flanges relax and reduce the bolt load. So we can see that, the flange end connection is not so 100 percent perfect.

Next we will talk about the threaded end connection, which is always utilized to connect the end of valves which is processed into taper pipe or straight pipe threaded with the taper tube thread joint or pipes. A relatively large leakage passages will occurred when connected by this way, so the sealing tape, sealant or filling material are needed to block the passages. Once the valve body can be welded, but if its expansion coefficient is too large or working temperature range is too wide, the threaded end connection has to be seal welded. And there are some restrictions of using this type of connection. For example, the suitable valve's diameter must be under DN 50. The valves with length less then DN 50 can adopt the fitting union as the pipe coupling, since the two parts of which can be jointed by the screw thread of the fitting union. Diameter above DN 50 would no be easy to install and seal the joint. So, the pipe coupling is available to the pipeline system at the appropriate points, as to make the installation and disassemble the valve joined easily.

And welded end connection, as the third type of end connection, which is quite reliable and other types. It can be widely used for various temperatures and pressure, even in terrible condition. However, it also has its own shortcoming. Since it is connected in welding way, it becomes more different to remove and reinstall. So they must be used in some suitable applications, such as nuclear project, ethylene project. In these fields, valves connected by welding are operated for quite a long time. And another thing need to be mentioned, because the socket weld end connection, there will appear a crevice between socket and pipe, which would be corroded day after day.

Original: http://www.chinavalmax.com/three-different-end-connections-for-valves.html

Edit by Ms. Yanwen Chan @ Ball Valves Blog.