COVER AS 4818452 - Caterpillar

Fuel Decrease
The pilot valve will move in the direction of the speeder spring (5) when either of the following conditions exist.
The force of compression in the speeder spring decreases (operator decreases desired rpm)
The axial force of the flyweights increases (load on the engine decreases)This opens the control ports (14). Oil from chamber (B) and pressure oil from the pump will dump through the end of the pilot valve bushing. The decreased pressure in chamber (B) will allow the power piston to move in the direction of the drive unit. The return spring (1) pushes against the strut assembly (4). This moves the output shaft lever (3). The action of the output shaft lever causes the counterclockwise rotation of the output shaft (2). This moves the fuel control linkage (15) in the "FUEL OFF" direction.
Illustration 13 g00332577
Earlier PSG governor (6) Power piston. (8) Needle valve. (10) Pilot valve compensating land. (11) Buffer piston. (14) Control ports. (A) Chamber. (B) Chamber.As power piston (6) moves in the direction of the drive unit the volume of chamber (A) decreases. This pushes the oil in chamber (A) into the chamber above the buffer piston (11). When the oil from chamber (A) flows into the power piston, the oil moves the buffer piston down in the bore of the power piston. The pressure at chamber (A) is more than the pressure at chamber (B). Chamber (A) is connected to the chamber above the pilot valve compensation land (10). Chamber (B) is connected to the chamber below the pilot valve compensation land (10). The pressure difference that is felt by the pilot valve compensation land, adds to the force of the speeder spring and moves the pilot valve down. This closes the control ports. When the flow of pressure oil from chamber (B) stops, the movement of the fuel control linkage stops.Hunting
There is a moment between the time the fuel control linkage stops its movement and the time the engine actually stops its increase or decrease of rpm. During this moment, the following two forces are changed on the pilot valve
The pressure difference at the pilot valve compensation land
The axial force of the flyweightsThe axial force of the flyweights changes until the engine stops its increase or decrease of rpm. The pressure difference at the pilot valve compensation land changes until the buffer piston returns to the original position. A needle valve (8) in a passage between chamber (A) and chamber (B) controls the rate at which the pressure difference changes. The pressure difference makes compensation for the change in the axial force of the flyweights until the engine stops its increase or decrease of rpm. If the force on the pilot valve compensation land plus the axial force of the flyweights is not is not equal to the force of the speeder spring, the pilot valve will move. This movement is known as hunting. Hunting is the movement of the pilot valve that is not the result of a change in load or desired