Fluid coupling

This article is about hydrodynamic fluid couplings, for "hydroviscous fluid couplings" see Viscous coupling unit.

A fluid coupling 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, where variable speed operation and controlled start-up without shock loading of the power transmission system is essential.