Rigid Coupling vs Flexible Coupling: When to Use Each

Aug. 12, 2022

Rigid Coupling vs Flexible Coupling: When to Use Each

There are two main types of grooved Couplings: Rigid Couplings and Flexible Couplings.

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Rigid Coupling


The characteristic of the Rigid Coupling is that the two adjacent pipe ports connected by it will not have the relative axial angle change and the displacement on the axis. This kind of pipe Coupling is mainly used in the riser pipe, empty rack pipe and other positions of the pipeline system.

The characteristic of the flexible pipe coupling is that a certain amount of relative angle and deflection are allowed in the axial direction of the adjacent two pipe ends connected by it. The allowable angle variable is related to the size of the pipe mouth, so it is also called a flexible Coupling. This kind of pipe joint is mainly used for buried pipes or large-diameter pipes. This is because the buried pipes have different degrees of ground settlement in different sections. The bottom surface of the trenches dug for laying the pipes is not necessarily flat, which will make The two adjacent sections of pipe are not on the same level. The flexible pipe Coupling can completely solve this problem because it can have axial deflection. Due to the heavy weight of large-diameter pipes, there will be a certain relative angle between the two ends of the pipe and the middle. Therefore, large-diameter pipes usually use flexible pipe Coupling, and generally pipes with a diameter of ≥ DN250 are often used.

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Flexible Pipe Coupling

In engineering construction, due to insufficient technical disclosure and quality control, workers often make no distinction between rigid Coupling and flexible Coupling and use them at will, which brings hidden dangers to the reliable operation and normal maintenance of the entire pipeline system. Such as a domestic hot water system, the temperature difference between the operating temperature of the system and the installation of the pipeline can reach 60℃, the length of the steel pipe is 6m, and the thermal expansion stress will reach 1200kg/mm2. If the pipe is rigidly connected, it will cause deformation of the bracket and cause damage to the pipe system. 

Therefore, the Coupling pipe fittings should be distinguished and selected reasonably.

① Domestic hot water pipelines, air-conditioning water pipelines, and open-air pipelines, in order to effectively compensate the pipeline displacement caused by thermal expansion and contraction, flexible Coupling must be used in the above three categories. If the displacement of the expansion section exceeds the total compensation amount of the flexible Coupling, the installation of a metal expansion Coupling should also be considered.

② Pipes with little temperature difference, such as indoor fire pipes, can use a large number of rigid Coupling. However, a certain number of flexible Coupling should be installed in the middle section of the long straight pipeline to compensate for a small amount of thermal expansion of the long straight pipeline section and ensure the safe operation of the entire pipeline system.

③  For elbows and broken-line pipes with temperature compensation, flexible Coupling should be installed on the pipe sections where angular displacement occurs.

④ It is recommended to use flexible Coupling for pump room piping to reduce noise and weaken vibration transmission.

⑤ Buried pipelines should adopt flexible Coupling, which can effectively deal with the local deformation of the pipeline system caused by uneven settlement.

⑥ The connection of small arc-shaped pipes must use flexible pipe Coupling. It can be assembled according to the straight pipe first, and then the pipe can be turned to make it reach the predetermined angle. However, in any case, the rotation angle shall not exceed the value specified in the specification of grooved pipe fittings.

Jianzhi provides high-quality Rigid Coupling and Flexible Coupling, welcome to inquire.


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