HOUSING 0857423 - Caterpillar

When the engine is running, left propel pump (14) and charge pump (17) rotate. The charge pump draws oil from the tank through the combined suction and return filter (16). Internal passages distribute output oil from the charge pump to the following components: charge relief valve (18), EDCs (1) and (2), EDC metering spool (3) and multifunction control valves (4) and (19) .When the propel lever is in the NEUTRAL position (or the machine ECM has disabled the propel system), EDCs (1) and (2) are not energized. Under these conditions, both ends of EDC metering spool (3) are open to the case drain, and the center envelope of the metering spool is active. The EDC metering spool blocks charge oil. The spool also opens a passage between propel pump's servo piston (13) and the pump case drain. The pump swashplate then moves to minimum angle.Charge oil that enters multifunction valves (4) and (19) seats the check valves and acts against makeup valves (7). Since left propel pump (14) rotates while the engine is running, normal leakage occurs in the left propel circuit. When pressure in the left propel circuit falls below charge pressure, the makeup valves open and the left propel circuit fills with charge oil. When the charge pressure in a circuit increases to 2700 200 kPa (392 29 psi), charge relief valve (18) opens. This action directs charge oil into the case drain of the left propel pump.The auxiliary hydraulic system controls the oil flow to and from parking brake cylinder (12) and shift cylinder (9). When the parking brake switch is in the ON position, the parking brake solenoid on the auxiliary manifold is not energized. Therefore, supply oil cannot flow to the parking brake cylinders, and the parking brakes are engaged. When the propel mode switch is in the PAVE position or in the MANEUVER position, the shift solenoid on the auxiliary manifold is not energized. Therefore, supply oil cannot flow to the shift cylinders.Note: For additional information about hydraulic control of the parking brake and shift solenoids, refer to Systems Operation, Testing and Adjusting, KENR9828.
Illustration 2 g02633137
Left Propel Hydraulic System (1) Forward EDC (2) Reverse EDC (3) EDC metering spool (4) Forward multifunction valve (5) Pressure limiter (6) Main relief valve (7) Makeup valve (8) From auxiliary hydraulic system (9) Shift cylinder (10) Final drive (11) From auxiliary hydraulic system (12) Parking brake cylinder (13) Servo piston (14) Left propel pump (15) To cooler bypass manifold port F (16) From hydraulic tank suction return filter (17) Charge pump (18) Charge relief valve (19) Reverse multifunction valve (20) Flushing relief valve (21) Flushing spool (22) To port "D" of cooler bypass manifold (23) Left propel motor (24) Motor output shaftNote: Since the right and left propel hydraulic circuits operate in the same manner, the following generic circuit description can be used to discuss either circuit. The left propel hydraulic circuit is shown in the above illustration.When the machine is traveling forward, the