The mechanical coupling is a new type of line connection device, which can replace the flange and the compensator providing connections for pipes and tubes, pipes and valves in various pipelines. In the same use occasions and conditions. The telescopic device has been widely used in petrochemical industry, ships, power and other industries in China. The expansion device is characterized in the chemical pipeline instead of the compensator. When installed, the connecting cover are respectively sheathed, the sealing ring and the sleeve should be installed on both sides of the pipe then tighten the bolts. At both ends of the pipeline in casing leave some space for axial slip, when the expansion and contraction of the pipeline can freely telescopic but no leakage.