Constant speed fluid coupling consists of two rotating elements each in the form of a bowl fitted with several straight radial vanes. These are positioned face to face within a casing that is partially filled with a measured quantity of fluid. One bowl called the impeller is connected to the prime mover shaft and acts as a centrifugal pump. The other bowl called runner is connected to the driven machine shaft and acts as a turbine. When the prime mover is started, the fluid is picked up in the vanes of the impeller and thrown outwards and across the gap into the vanes of the runner. As a result, the runner begins to rotate and transmit the power to the driven machine. There is no mechanical connection between the input and output shaft of fluid coupling, and transmission of power is done by the hydro-kinetic energy of the fluid in the casing. A precisely controlled, fixed amount of oil ensures consistent output speed for smooth and uninterrupted operation.