Let’s look briefly at the operation principle of a fluid coupling and consider a situation as shown in the diagram where two fans are positioned facing each other. If fan A is operated to produce a flow of air (or, in other words, to force air to move), this air will be directed at the vanes of fan B, causing it to rotate also. A fluid coupling performs the transfer of torque in a fashion which is similar to this transfer of motion by the fans.
Referring again to the example in the above diagram, the flow of air that passes through fan B still possesses a considerable amount of energy. And if ducts are used to redirect this air flow to the rear of the vanes in fan A, then the rotation of that fan will be assisted and torque will be subsequently increased. It is this principle upon which the operation of a torque converter is based.
If we compare the above example with the condition of an actual torque converter, we can see that the pump fills the role of fan A, the turbine fills the role of fan B, and the stator fills the role of the ducting.