The difference between coupling and union
The union is generally used for the front end and the back end of the pipeline with valves, water meters and other equipment, to facilitate the disassembly and maintenance of these equipment, the middle is to rely on the clamping tight sealing pad to seal. A union is a detachable piece of pipe, that is, something connected through a union that can be removed and replaced, such as a valve.
The coupling is connected with two pieces of steel (with same diameter and reducing diameter) by screw thread. The seal at the joint is screw thread seal.A coupling is a piece of pipe in a pipe. If the pipe is longer than the length of the pipe, the coupling will be used.
Union, generally used in the threaded connection pipe, more in the pipe small diameter, a little larger pipe diameter is generally connected with flange and other ways, also easy to disassemble. Coupling threaded, butt welded, socket; union only threaded and socket union, and even socket union threaded to be unscrewed. With a union there is no need to turn the pipe. If there is no threaded connection of the union, the connection must be removed by moving the pipe.
From the practical application, the union is used in low pressure and the coupling is used in high pressure. Union is a threaded connection, generally used in public works under 10kg.
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