PILOT VALVE OPERATION

WOODWARD PSG GOVERNORS - TM-55-1930-209-14P-9-2_217

TM-55-1930-209-14P-9-2 Water Purification Barges (NSN 1930-01-234-2165) Fuel Oil System Manual
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WOODWARD PSG GOVERNORS SYSTEMS OPERATION INTRODUCTION The Woodward PSG (Pressure compensated Simple Governor) can operate as an isochronous or a speed droop type governor. It uses engine lubrication oil, increased to a pressure of 175 psi (1200 kPa) by a gear type pump inside the governor, to give hydra/mechanical speed control. PILOT VALVE OPERATION The fuel injection pump camshaft drives a governor drive unit. This unit turns pilot valve bushing (13) clockwise as seen from the drive unit end of the governor. The pilot valve bushing is connected to a spring driven ballhead. Flyweights (7) are fastened to the ballhead by pivot pins. The centrifugal force caused by the rotation of the pilot valve bushing causes the flyweights to pivot out. This action of the flyweights changes the centrifugal force to axial force against speeder spring (5). There is a thrust bearing (9) between the toes of the flyweights and the seat for the speeder spring. Pilot valve (12) is fastened to the seat for the speeder spring. Movement of the pilot valve is controlled by the action of the flyweights against the force of the speeder spring. The engine is at the governed (desired) rpm when the axial force of the flyweights is the same as the force of compression in the speeder spring. The flyweights will be in the position shown. Control ports (14) will be closed by the pilot valve. Fuel Increase When the force of compression in the speeder. spring increases (operator increases desired rpm) or the axial force of the flyweights decreases (load on the engine increases) the pilot valve will move in the direction of the drive unit. This opens control ports (14). Pressure oil flows through a passage in the base to chamber (B). The increased pressure in chamber (B) causes power piston (6) to move. The power piston pushes strut assembly (4), that is connected to output shaft lever (3). The action of the output shaft lever causes clockwise rotation of output shaft (2). This moves fuel control linkage (15) in the FUEL ON direction. PSG GOVERNOR INSTALLED 2. Output shaft. 15. Fuel control linkage. As the power piston moves in the direction of return spring (1) the volume of chamber (A) increases. The pressure in chamber (A) decreases. This pulls the oil from the chamber inside the power piston, above buffer piston (11) into chamber (A). As the oil moves out from above buffer piston (11) to fill chamber (A) the buffer piston moves up in the bore of the power piston. Chambers (A and B) are connected respectively to the chambers above and below the pilot valve compensating land (10). The pressure difference felt by the pilot valve compensating land adds to the axial force of the flyweights to move the pilot valve up and close the control ports. When the flow of pressure oil to chamber (B) stops so does the movement of the fuel control linkage. Fuel Decrease When the force of compression in the speeder spring decreases (operator decreases desired rpm) or the axial force of the flyweights increases (load on the engine decreases) the pilot valve will move in the direction of speeder spring (5). This opens 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 let the power piston move in the direction of the drive unit. Return spring (I) pushes against strut assembly (4). This moves output shaft lever (3). The action of the output shaft lever causes counterclockwise rotation of output shaft (2). This moves fuel control linkage (15) in the FUEL OFF direction. 7

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