Diesel Engine Fundamentals
DIESEL ENGINE SPEED,
FUEL CONTROLS, AND PROTECTION
Simplified Operation of the Governor
The governor controls the fuel rack position through a combined action of the hydraulic
piston and a set of mechanical flyweights, which are driven by the engine blower shaft.
Figure 28 provides an illustration of a functional diagram of a mechanical-hydraulic
governor. The position of the flyweights is determined by the speed of the engine. As
the engine speeds up or down, the weights move in or out. The movement of the
flyweights, due to a change in engine speed, moves a small piston (pilot valve) in the
governor's hydraulic system. This motion adjusts flow of hydraulic fluid to a large
hydraulic piston (servo-motor piston). The large hydraulic piston is linked to the fuel
rack and its motion resets the fuel rack for increased/decreased fuel.
Figure 28 Simplified Mechanical-Hydraulic Governor