Fluid Coupling – Main Parts, Principle, Working, Application, Advantage and Disadvantages

Fluid Coupling – Main Parts, Principle , Working and Application

The fluid coupling is also referred to as hydraulic coupling, which is used in the use of a transmission fluid to transfer rotating power from shaft to shaft. It is used in the vehicle transmission, marine and power transmission industries. It is used as a mechanical seizure alternative.

Dr. Hermann Fottinger has discovered it. In 1950, he patented his finding of fluid coupling and torque converter.

Main Parts

It has three main elements:
  1. Housing: The shell is also named. The seal around the drive shaft is oilproof. It also protects against external damage to the impeller and turbine.
  2. Impeller or pump: is a turbine that is attached and called the impeller to the input shaft. The pump is also known as a centrifugal pump.
  3. Turbine: attached to the power source that is to be distributed with rotating electricity. 
The rotor is attached to the main motor (internal combustion motor) that is a source of power. The turbine is connected to the output shaft where rotational power is necessary. The rotor and turbine is located in a sealed housing which is oil-tight. The housing is made up of fluid transmission.

Working Principle

The fluid operating principle can easily be explained by the use of two fans, one with the power supplies and one with the power supply. The air from the first fan begins blowing in the direction of the second fan when the power switch is on (which is not connected to the energy source). At first it can not drive the second fan when the first fan blows at lower speed. But as the powerful fan speed increases, the air speed reaching the second fan blades also increases and rotations begin. It gets the same speed as the first fan after some time.

The fluid relation works on the same principle. The rotor is the first fan and the turbine is the second fan. In an oil-tight housing are the impeller and the turbine. The rotor is connected to the input shaft of the primary mover and the turbine. The fluid in the housing becomes centrifugal when the impeller is being driven through the primary mover and, thanks to its angled vanes, the fluid is guided to the turbine blades.

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.


  • 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.


  • The power transmission is free from vibration and noises.
  • Power transmission is smooth even in extreme condition.
  • Overload protection.
  • Motor or engine starts unloaded.


  • There is always slip. There is always slight difference in speed of impeller and runner.
  • Fluid coupling cannot develop torque when the driving shaft and driven shaft are rotating in same angular velocity.
  • Under stalling condition, the coupling dissipates energy as heat it may lead to damage.

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