Types and Functions of Flexible Couplings

What is Flexible Coupling?

In situations where two shafts of a given mechanism are misaligned, flexible couplings are used to transmit torque from one shaft to another. These couplings can accommodate differing degrees of misalignment approximately up to 3°. In addition to this feature, the couplings are also used for noise reduction and vibration damping.

There are three Basic Functions involved under this category, and they are:

1. Transmit Power: Basically couplings are used to transmit mechanical power from one device to another. This power is in the form of mechanical torque which is found at some given speed. However, the power lost by a coupling is very small in amount, but still exhibit some efficiency as compared to others.

2. Compensate for Axial Displacement or End Movement: These couplings are designed to accommodate axial movement of the joint shafts ends or equipment. The end movement and accommodation of misalignment is done without the need to induce any irregular loads in the equipment. During the installation the alignment of shaft ends and machines is very important. It is then the coupling will allow the thermal growth of the overall device.

3. Accommodate Misalignment: Under this function there are two more sub-functions involved such as Shaft misalignment and Coupling misalignment.

    • Shaft misalignment deals with the relationship between the driven shafts and the driver. This type is further broken into two more categories namely angular misalignment and parallel offset.


  • Coupling misalignment comes into picture when the coupling has to accommodate for shaft misalignment. This category too has two general approaches namely; double-flex coupling like a diaphragm coupling and the other is the elastomeric coupling.

Flexible couplings are made up of many materials including rubber, metal, PVC each belonging to a piping system. Whether it is for ventilation or plumbing, couplings work well in unusual angles and in tight spaces.

Types of Flexible Coupling

    • Flexible Plastic Drain Connectors: This type of coupling is used for modifications and repair work below bathroom sink and kitchen fixtures. This type usually twists and turns for about 180 degrees and stays into position when put to use.


    • Jaw Couplings: A locking ring is available to secure a split insert. The main advantage is that the insert can be replaced without shifting the two hubs.


    • Flexible Rubber Coupling: This type of coupling is useful in pluming applications for installation and repair of drain, vent and waste lines. It is available as a straight cylinder, bent at 90 or 180 degree angle formed into a P-trap.


  • Flexible Ventilation Duct Coupling: Used in HVAC to manage unusual turns and twists in heating, ventilation and exhaust systems.

Similarly, there are several other types to list under this category. In a nutshell, the joints in these shaft flexible couplings allow continuity of the system while imparting flexibility to easily accommodate misalignment.

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