In this post, we’re going to look at the types of coupling available on the market and the types of applications they’re best suited to.

What is a coupling?

A coupling is a precision-engineered mechanical device. Couplings are used to connect two shafts of the same or differing dimensions in order to transmit power. BE Power Transmission supply SIT SpA drive shaft couplings.

In general, their main purpose is to form a connection between two sections of rotating devices. This also allows for a limited amount of misalignment or movement whilst still transmitting the drive.

In short, a coupling is a mechanical device used in a wide range of applications including pumps, motors, compressors and generators.

The Importance of coupling selection

Couplings are a vital part of the equipment in which they are located. Correct selection and specification can be extremely important in terms of achieving increased levels of reliability. This will also contribute to reduced maintenance costs over the life cycle of a piece of equipment.

Correctly installed, couplings will successfully transmit torque and compensate for degrees of misalignment (parallel, axial and angular). Perhaps most importantly, they allow for dynamic fine-tuning and smooth operation.

What do couplings do?

Moving equipment is designed in different ways with differing operating systems. Couplings are specified in terms of load, torque transmission, shaft size, pressure and safety requirements to transmit drive.

What power transmission coupling should I choose?

Different types of coupling have been developed to match individual applications. Each type and design offers different operational advantages. Most can be classified into three types:-

  • Rigid coupling
  • Flexible coupling
  • Fluid coupling

Most shaft couplings are designed for transmitting power from one end to another, ie from a motor to a pump unit. However, applications are diverse and couplings can also serve to:-

  • Play a role in altering vibration characteristics
  • As a connection between the drive and the driven element of a piece of equipment
  • To protect against excess torque transmission and equipment damage
  • To avoid overload events
  • To smooth out the transmission of shock loads within a piece of equipment

More specialist torque-limiting couplings are available. These are installed to disconnect automatically if pre-set torque limits are exceeded, to avoid equipment damage.

What different types of coupling are there?

There is a wide range of coupling designs and materials to match differing applications within the field of engineering and associated disciplines. Here, we look at a selection of couplings commonly used in industry today.

Flexible couplings

SIT Sitex ST Flexible Coupling

The most common type of coupling is a flexible coupling, designed for torque transmission.

These are specified when the two shafts or the drive and driven unit are misaligned, permitting radial and axial displacement and rotation. They serve to facilitate the smooth transmission of both rotational speed and torque.

Typical applications for flexible couplings

  • Electric motor drives
  • High temperature operation
  • For use where oils and chemicals may be present
  • Constant and low inertia applications

SIT Sitex ST flexible couplings supplied by BE Power Transmission are manufactured in high-quality steel and feature the OPTIGEAR profile for high torque transmission.

Rigid coupling

Rigid couplings are used in applications connecting two shafts in precise radial and axial alignment. There can be little or no relative movement (less than one degree of deflection) between the two.

Typical applications for rigid couplings

  • Processing equipment
  • Domestic appliances such as washing machines and lawn mowers
  • Some medical equipment
  • Smaller wind turbines

Bellows couplings

SIT Servoplus Bellow Coupling

Bellows couplings are flexible couplings consisting of two sections connected by a bellows. They combine exceptional torsional rigidity with a small degree of flexibility afforded by the bellows.

This facilitates effective operation despite axial or parallel misalignment between the connected shafts or sections.

Applications for bellows couplings

  • Where high precision positioning is required operationally
  • High temperature environments
  • Precision equipment used where temperature may fluctuate significantly
  • Applications requiring high levels of torsional rigidity

SIT Servoplus bellow couplings provide high levels of torsional rigidity.

Elastic couplings

SIT JUBOFLEX Elastic Coupling

Elastic couplings transmit torque is using an elastic component. This compensates for any relative axial displacement and absorbs shocks where the sections join.

In general, elastic couplings result in reduced maintenance requirements. Elastic materials will wear out long before the metal components of the coupling. Elastic couplings generally do not require lubrication.

SIT JUBOFLEX couplings supplied by BE Transmission include an elastic element and are reinforced with steel for performance.

Disc couplings

Disc couplings are a flexible shaft coupling where the torque and drive are transmitted via a series of flexing discs.

The coupling is made up of two hubs, the requisite number of disc packs and a centrepiece. The focus is to minimise any misalignment forces on the pieces of equipment connected by the coupling.

Disc couplings are used for high speed, high performance applications, capable of handling speeds up to 10,000 rpm.

Rubber couplings

Rubber couplings are used in a wide variety of industrial applications. They are selected where soft properties are required together with the ability to damp unwanted torsional vibrations.


Choosing the correct types of couplings will enhance the performance and longevity of rotating equipment. Couplings should be easy to connect and disconnect. Installed correctly, they will transmit power from shaft to shaft without loss of drive. They will reduce shock load transmission and hold the shaft in good alignment.

If you have a requirement for SIT SpA couplings then please contact BE Power Transmission on 01274 309071.