1. FLUID COUPLINGS

2. ABOUT
A fluid coupling (also known as a fluid clutch or hydraulic coupling) is a hydrodynamic device used to transmit rotating mechanical power. It has been used in automobile transmissions as an alternative to a mechanical clutch. It also has widespread application in marine and industrial machine drives such as diesel locomotives.

4. YOUTUBE ANIMATION
Here the principle is explained in a easy to follow video clip, note how the 2 halves do not make contact with each other:

5. INTERIOR PARTS

6. Advantages/Disadvantages
Easy start-up with gradual acceleration of the driven component
Controlled start-up without shock loading of the power transmission system is essential.
Rotational vibrations are dampened
Overload protection
Disadvantages:
Design limitations
Great difficulty to control precisely

7. REFERENCES:
couplings-fluid.php coupling-to-slip-at-low-speeds