The hydraulic fluid coupling, or Vulkan Coupling as it is more commonly referred to, is a device that is situated between the Werkspoor power take off (PTO) and the propeller shaft. Pictured centre photo is the Ross Revenge coupling that measures 2.4m in diameter - and foreground is the hydraulic actuator that is used in conjunction with the vari pitch propeller.
Designed and manufactured by the Vulkan Group in 1959 the fluid couplings purpose was to act as a clutch type mechanism between the main engine and the propeller, as both of these introduced stresses and strains that had to be managed in some way.
As with any engine the size of the Werkspoor, the engine's initial startup would have produced torsional vibration and likewise the vari pitch propeller would also have introduced shock loading to the prop shaft. Both of these issues had to be dealt with by means of dampening.
The hydraulic fluid coupling is made up of three components, i) the oil tight housing ii) 2 turbines (fan like components) - one connected to the input shaft [primary wheel - (the pump)] with the other connected to the output shaft [secondary wheel], and of course iii) the hydraulic oil.
The primary wheel is driven by the Werkspoor engine producing both linear and rotational force to the fluid. This action produces a flow of fluid in the direction to the secondary wheel, the output turbine.
At this point any differences in angular velocities of the primary and secondary wheels' result in the secondary wheel causing a torque, enabling it to rotate in the same direction as the primary wheel.
The video below shows how this was achieved in practice.
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