SPRING 3P0768 - Caterpillar

Introduction
This chapter describes the operation of the PSG governor, including a description of the hydraulic system and the way it operates.Figure 3-1 and 3-2 show the relationship of the various parts.Operation
Mechanical Hydraulic System
Figure 3-1 shows the oil supply coming from the engine lubricating system. It bypasses the relief valve into the governor oil pump where its pressure is increased to either 517, 1207, or 1896 kPa (75, 175, or 275 psi) above inlet pressure. Four check valves permit rotation of the governor in either direction. Some models have two of the passages plugged for rotation in one direction only.Relief-valve discharge is back to supply, so unused oil is recirculated within the governor.Pressured oil is supplied though oil passages to the pilot-valve system. The pilot-valve system is a three-way spool valve. It applies pressured oil to the power cylinder when an under-speed signal is received or releases trapped oil from the power cylinder when a over speed signal is received.Oil flow into the power cylinder forces the power piston upward against the force of the return spring. Pressured oil displaces the buffer piston and forces oil into the upper annulus.Because all moving parts of the PSG are immersed in oil during normal operation the governor has extremely long wear without changes of