Exam Question

### (a) Mechanical Hydraulic Governor (4 Marks)
A Mechanical Hydraulic Governor is a device used to maintain the speed of a prime mover, such as a marine diesel engine, at a desired value irrespective of load changes. It is a proportional controller that operates by combining a mechanical speed-sensing mechanism with a hydraulic power-amplifying system.
* **Mechanical Section (Sensing Element):** This part consists of rotating flyweights (ballheads) which are mechanically driven by the engine's crankshaft. The centrifugal force generated by the rotation of these flyweights is proportional to the square of the engine speed. This force is opposed by a pre-tensioned speeder spring, whose compression can be adjusted to set the desired engine speed.
* **Hydraulic Section (Actuating/Power Element):** This part acts as a hydraulic amplifier. The small mechanical movement of the flyweights is insufficient to move the large and heavy fuel racks of an engine. This movement is therefore used to actuate a pilot valve. The pilot valve directs high-pressure oil to a power piston (servomotor), which is connected via linkages to the engine's fuel racks. The hydraulic pressure provides the significant force required for fuel regulation.