Fluid coupling, also referred to as hydraulic coupling, is one of the popular hydrodynamic devices used for transferring rotational torque using transmission fluid. It is mostly used as an alternative to the mechanical clutch
. The design of fluid coupling comprises of three main parts: 1) Housing: This is also referred to as a shell. It is designed with an oil-tight seal that fits firmly around the drive shaft. The seal is also used to protect the turbine and impeller from outside damage.2) Pump or impeller: This is a turbine that is connected to the input shaft. It is also referred to as a pump since it runs as a centrifugal pump.3) Turbine: This is the output shaft. The working principle of fluid coupling is simple. When an impeller (driver shaft) rotates and turns fluid at high speed, it will also rotate another shaft (driven shaft) in the same housing through centrifugal force. As the impeller rotates faster, it increases the speed such that the driver and drive shaft rotates at the same rate.