WOODWARD PSG GOVERNORSSYSTEMS OPERATIONPSG GOVERNOR6. Power piston. 8. Needle valve. 10. Pilot valvecompensating land. 11. Buffer piston. 14. Controlports. A. Chamber. B. Chamber.As power piston (6) moves in the direction of thedrive unit the volume of chamber (A) decreases. Thispushes the oil in chamber (A) into the chamber abovebuffer piston (II11). As the oil from chamber (A) flowsinto the power piston it moves the buffer piston down inthe bore of the power piston. The pressure at chamber(A) is more than the pressure at chamber (B).Chambers (A and B) are connected respectively tochambers above and below the pilot valve compensatingland (10). The pressure difference felt by the pilot valvecompensating land adds to the force of the speederspring to move the pilot valve down and close the controlports. When the flow of oil from chamber (B) stops sodoes the movement of the fuel control linkage.HuntingThere is a moment between the time the fuel controllinkage stops its movement and the time the engineactually stops its increases or decrease of rpm. Duringthis moment there is a change in two forces on the pilotvalve, the pressure difference at the pilot valvecompensating land and the axial force of the flyweights.The axial force of the flyweights changes until theengine stops its increase or decrease of rpm. Thepressure difference at the pilot valve compensating landchanges until the buffer piston returns to its originalposition. A needle valve (8) in a passage between space(A) and (B) controls the rate at which the pressuredifference changes. The pressure difference makescompensation for the axial force of the flyweights untilthe engine stops it increase or decrease of rpm. If theforce on the pilot valve compensating land plus the axialforce of the flyweights is not equal to the force of thespeeder spring the pilot valve will move. This movementis known as hunting (movement of the pilot valve that isnot the result of a change in load or desired rpm of theengine).The governor will hunt each time the engine actuallystops its increase or decrease of rpm at any other rpmthan that desired. The governor will hunt more after arapid or large change of load or desired rpm than after agradual or small change.PSG GOVERNOR8. Needle valve.NOTE: The Woodward PSG Governor is removed fromthe engine to show the needle valve (8). When thegovernor is installed on the engine, the needle valve (8)is between the governor and the cylinder block.SPEED ADJUSTMENTPSG governors use a clutch assembly (2) driven bya 110V AC/DC or 24V DC reversible synchronizing motor(1) to move link assembly (3) up or down. The clutchassembly protects the motor if the adjustment is runagainst the stops. The motor is controlled by a switchthat is remotely mounted. The clutch assembly can beturned manually if necessary.PSG GOVERNOR1. Synchronizing motor. 2. Clutch assembly. 3.Link assembly8
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