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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