ENGINE AR-PRIMARY 3681859 - Caterpillar

Illustration 1 g03839186
(1) Displacement change valve for the left travel motor (2) Displacement change valve for the right travel motor (3) Line (pilot) (4) Swing parking brake (5) Main control valve (6) Main pump (7) Supply line (8) Parallel feeder passage (9) Pilot manifold (10) Passage (11) Inline filter (12) Pressure reducing valve (13) Passage (14) Center bypass (15) Travel speed solenoid valve (16) Hydraulic activation solenoid valve (17) Pilot control valve (stick and swing) (18) Pilot control valve (bucket and boom) (19) Pilot control valve (travel) (20) Passage (boom lower) (21) Boom control valve (22) Passage (boom raise) (23) Hydraulic tank (24) Left travel control valve (25) Right travel control valve (26) Passage (27) Passage (28) Passage (29) Line (pilot) (30) Signal line (load sense) (31) Proportional pressure compensator (32) Swing control valve (33) Line (pilot) (34) Valve (swing parking brake) (35) Two-speed travel switch (36) Two-speed travel relay (37) Hydraulic lockout switchPilot Oil Circuit
Oil flow is supplied to the pilot system from main pump (6). The pilot system performs the following functions.
Reduce main system pressure to pilot pressure in order to operate the control devices.
Provide pilot oil pressure to travel pilot control valve (19), stick and swing pilot control valve (17), and boom and bucket pilot control valve (18) .
Provide pilot oil pressure to the swing brake control valve (34) and displacement change valves (1) and (2) .Oil from main pump (6) flows through line (7) and into parallel feeder passage (8). The hydraulic oil flows from parallel feeder passage (8) to pilot manifold (9). Oil flows through pilot manifold (9), through passage (10), and into inline filter (11). The oil then flows into pressure reducing valve (12) and into passage (13). The oil in passage (13) divides into three paths. The first path is into, center bypass (14). The second path is through travel speed solenoid valve (15). The third path is through hydraulic activation solenoid valve (16) .The pressure within the pilot system is regulated by pressure reducing valve (12) .Pilot Control Valve Circuits
When the hydraulic activation control lever is placed in the UNLOCKED position, hydraulic lockout switch (37) closes. This action activates hydraulic activation solenoid valve (16) .The pilot oil flows through pilot manifold (9) to passage (10). Then, the oil flows to the following pilot control valves: stick and swing (17), bucket and boom (18) and travel (19). When any of the pilot control valves are operated, the pilot oil flows to the selected valve within the main control valve. The pilot oil shifts the stem of the selected control valve.Implement Circuit
Note: The following examples are for a BOOM LOWER and a BOOM RAISE function. A stick, bucket, swing, or travel function have a similar operation.When the joystick for the boom is moved to the BOOM LOWER position, pilot oil from pilot control valve (18) flows to passage (20). The pilot pressure shifts boom control valve (21). The oil delivery from main pump (6) flows to the rod end of the