Fluid Coupling - Main Parts, Principle , Working and Application

Fluid coupling is also known as hydraulic coupling is a hydrodynamic device which is used to transfer rotational power from one shaft to another by the use of transmission fluid. It is used in automotive transmission system, marine propulsion system and in industries for power transmission. It is used as an alternative for the mechanical clutch.

It was discovered by Dr. Hermann Fottinger. He patented his discovery of fluid coupling and torque converter in the year 1950.

Main Parts

It consists of three main components
  1. Housing: It is also known as the shell. It has oil-tight seal around the drive shaft. It also protects the impeller and turbine from outside damage.
  2. Impeller or pump: It is a turbine which is connected to the input shaft and called as impeller. It is also known as pump because it acts as a centrifugal pump.
  3. Turbine: It is connected to the output shaft to which the rotational power is to be transmitted.

The impeller is connected to the prime mover (internal combustion engine) which is a power source. The turbine is connected to the output shaft where rotation power is needed to be transmitted. The impeller and turbine is enclosed in an oil-tight sealed housing. The housing consists of transmission fluid.

Working Principle

The working principle of fluid can be easily explained by the taking two fans in which one is connected to the power supply and other is not. When the power switch is ON, the air from the first fan is starts to blow towards the second fan (which is not connected to the power source). Initially when the first fan is blowing at lower speed, it does not able to drive the second fan. But as the speed of the powered fan increases, the speed of air striking the blades of second fan also increases and it starts to rotate. After some time it acquires the same velocity of that of the first fan.

On the same principle the fluid coupling works. In that the impeller act as first fan and the turbine act as second fan. Both impeller and turbine enclosed in an oil tight housing. The impeller is connected the input shaft of the prime mover and the turbine with the output shaft. When the impeller is moved by the prime mover, the fluid in housing experiences centrifugal force and due to curved vanes of the impeller the fluid directed towards the turbine blades. As the fluid strikes the turbine blades it starts rotating. With the increase in the speed of impeller, the velocity of the turbine increases and becomes approximately equal to the impeller speed. The fluid after passing through the turbine blades again return to the impeller.

Also Read: How Ignition Distributor Works?

Working of Fluid Coupling

  1. As the prime mover moves, it rotates the impeller of the coupling. The impeller acts as a centrifugal pump and throws the fluid outward and directs it towards the turbine blade.
  2. As the high moving fluid strikes the turbine blades, it also starts rotating, after striking on the blades, the direction of the fluid is changed and it is directed towards the impeller again. The blades of turbine are designed in such a way that it can easily change the direction of the fluid. It is the changing of direction of the fluid that makes the turbine to rotate.
  3. As the impeller speed increases, the speed of the turbine also increases. After sometime the speed of both impeller and turbine becomes equal. In this way power is transmitted from one shaft to another by the use of fluid coupling.
  4. In same way torque converter works but the difference is that it has stator placed in between impeller and turbine for torque multiplication.
For better explanation watch the video given below:


  • It is used in automotive industries for the transmission of power from the engine to the wheel as alternative of clutch.
  • It is used in marine propulsion systems.
  • It is used in various industries for the power transmission.
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