The oil supply is from the engine lubrication system. This oil is supplied to the governor oil pump which boosts it to 175 psi (12,3 kg/cm2). Four check valves permit rotation of the governor in either direction. Relief valve discharge is back to supply, so unused oil is recirculated within the governor.
GOVERNOR OIL FLOW SCHEMATIC
The governor drive shaft is hydraulic valve bushing (7). Pilot valve plunger (5), in the hollow center of the bushing, screws into thrust bearing and spring seat (2). The bushing drives weights (1); the toes of the weights rest against the thrust bearing and spring seat. One of hydraulic pump gears (9) is integral with bushing (7).
When the load on the engine increases, the rpm of the engine decreases and the rotating speed of governor weights (1) decreases. Governor weight centrifugal force is less and governor spring (3) pushes spring seat (2) and pilot valve plunger (5) to a position in bushing (7) where an oil passage is opened and oil is directed to power piston (6). The pressure of the oil moves the power piston which moves lever (4). The lever is the part of the governor terminal shaft which is linked to the engine fuel rack. The fuel rack is moved to a more fuel position and the rpm of the engine increases. As the engine rpm increases, governor weights (1) rotate faster, centrifugal force is greater and the toes of the weights move thrust bearing and spring seat (2) connected to pilot valve plunger (5). When the rpm of the engine is again the same as it was before the load increased, the governor weights will have moved the pilot valve plunger to its original position, closing the oil passage to power piston (6) to stop the movement of the power piston and engine fuel rack.
When the load on the engine decreases, the rpm of the engine increases and the rotating speed of governor weights (1) increase. The toes on the governor weights move thrust bearing and spring seat (2) and pilot valve plunger (5) to a position in bushing (7) that allows the oil under power piston (6) to drain. When the oil under the power piston can drain, a spring in the governor linkage (not part of the governor) moves the engine fuel rack to a lesser fuel position and the rpm of the engine decreases. The governor weights rotate slower and governor spring (3) pushes on spring seat (2) and pilot valve plunger (5). When the rpm of the engine is again the same as it was before the load decreased, the governor spring will have pushed the pilot valve plunger to a position where oil can no longer drain from under power piston (6) and the movement of the power piston and fuel rack is stopped.
HYDRAULIC GOVERNOR (CROSS SECTION)
1. Weights (two in ball head assembly). 2. Thrust bearing and spring seat. 3. Governor spring. 4. Lever (terminal shaft). 5. Pilot valve plunger. 6. Power piston. 7. Bushing (drive shaft). 8. Buffer piston. 9. Hydraulic pump gears. 10. Buffer springs (two).
The sensitivity of governor weights (1) and governor spring (3) to the slightest variations in engine rpm are absorbed by buffer springs (10) that center buffer piston (8) in power piston (6). The oil directed to the power piston must first pass through an opening in the bottom of the power piston and act on the buffer piston to move the power piston.
The hydraulic governor is a zero percent speed droop governor (isochronous). Speed droop is the percent difference between the rpm of an engine operating under no load and the rpm of an engine operating under full load. The percent of speed droop is calculated by using the following equation.
