The working principle of fluid can be easily explained by the taking of two fans which is connected to the power supply and other is not. When the power switch is ON, air from the first fan starts to blow towards the second fan, the one unconnected to the power source. Initially when the first fan is blowing at lower speed, it does not able to drive the second fan. 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 requires the sane velocity of the first fan. On this same principle the fluid coupling works. The impeller act as first fan and the turbine acts as second fan. Both the impeller and turbine enclosed in an oil tight housing. The impeller is connected to the input shaft of the prime mover and the turbine to the output shaft. When the impeller is moved by the prime mover, the fluid in the housing experiences centrifugal force and due to the curved vanes of the impeller the fluid is directed towards the turbine blades. As the fluid strikes the turbine blades it starts rotating. With the increase in the speed of the 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. 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. 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 it is directed towards the impeller again. The blades of turbine are designed in such a way that it can be easily change the direction of the fluid. It is changing in the direction of the fluid that makes the turbine to rotate. As the impeller speed increases, the speed of the turbine also increases. After sometime the speed of both the impeller and the turbine becomes equal. In this way power is transmitted from one shaft to another by the use of fluid coupling. In the same way torque converter works but the difference is that it has a stator placed in between the impeller and turbine for torque multiplication.