Hydraulic Schematic For Pilot Oil
 | |
| Illustration 1 | g00632625 |
(1) Displacement change valve (left travel) (2) Displacement change valve (right travel) (3) Valve for swing parking brake (4) Control valve for swing parking brake (5) Line (6) Line (7) Swing boom and blade control valve (8) Line (9) Line (10) Control valve for Boom I (11) Left travel control valve (12) Passage (13) Line (14) Main control valves (15) Selector valve (16) Passage (17) Passage (18) Straight travel valve (19) Right travel control valve (20) Hydraulic activation control valve (21) Boom drift reduction valve (22) Main relief valve (23) Spool (25) Passage (26) Passage (29) Pilot control valve (swing boom) (30) Pilot control valve (travel) (31) Pilot control valve (stick and swing) (32) Pilot control valve (bucket and boom) (33) Line (34) Line (35) Accumulator (36) Passage (37) Line (38) Line (39) Line (40) Solenoid valve for power mode (41) Line (42) Passage (43) Pilot relief valve (44) Travel speed solenoid valve (45) Passage (46) Shuttle valve (47) Pressure switch (48) Pump for the swing boom and blade (49) Pilot pump (50) Left pump (51) Right pump (54) Pilot manifold (55) Line (56) Spool (switch to no-load condition) (57) Line (58) Line (59) Line (60) Line (61) Shuttle valves (62) Shuttle valves (63) Line (64) Pilot filter (65) Pressure reducing valve (66) Swashplate and regulator assembly for the main pump | |
Pilot Oil Circuit
Pilot system oil from pilot pump (49) has the following three main functions:
(1) Control main pump output.
(2) Provide an easier operation of the control levers.
(3) Create pilot oil pressure in order to achieve various operations.
The pilot oil from pilot pump (49) flows through pilot filter (64) and line (58). The pilot oil then enters pilot oil manifold (54). The pilot oil is then separated into the following circuits through respective lines (33) and (34), and passages (36), (42), and (45) .
Main Pump Circuit
Pilot oil from passage (42) goes to the solenoid valve for power mode (40). The pilot oil is changed to a hydraulic signal of power shift pressure. The hydraulic signal goes through line (57) to the main pump regulator. This controls the pump output.
Power shift pressure causes an increase or a decrease of the pump output flow. When the machine is operated, the hydraulic oil flows from shuttle valve (62) through line (63). The hydraulic oil then enters the pump regulator in order to perform flow control.
Note: For more information on the regulators and main pumps, refer to Systems Operation, "Piston Pump (Main)".
Pilot Control Valve Circuits
The pilot control valve is the main component in the pilot system. The pilot oil in passage (36) goes through line (34) to hydraulic activation control valve 20. The pilot oil then goes to pilot control valves (30), (31), (32) and (29) through respective pilot lines. When a pilot control valve is operated, pilot oil goes to the main control valve that is selected. The pilot oil shifts the stem of the selected main control valve in order to operate a cylinder and/or a motor.
The operation of a pilot control valve is described in the following example:
When the boom control lever is moved to the RAISE position, pilot oil from line (39) shiftsthe stem in control valve (10) upward. When the boom control lever is moved to the LOWER position, pilot oil from line (8) shifts the stem in control valve (10) downward. When the boom is lowered, the pilot oil from line (9) activates boom drift reduction valve (21) .
Note: For more information on boom drift reduction valves, refer to Systems Operation, "Boom Hydraulic System".
Main Control Valve
Pilot circuits in the main control valves direct pilot oil from line (36) through line (33) to main control valves (14). The oil then separates into two separate oil flows which go to passage (12) and passage (26). When the main control valves are in the NEUTRAL position, oil pressure in passages (12) and (26) remains low. When the travel control is operated, oil pressure in passage (12) increases. When swing control or implement control is activated, oil pressure in passage (26) increases.
Pilot oil from passages (12) and (26) goes through respective lines (38) and (37) to shuttle valve (46). The pilot oil then goes through line (41) to spool (56) (load signal to the main pump ). When no hydraulic control is activated, oil pressure from line (41) does not activate spool (56). This allows pilot oil flow from line (60) through pressure reducing valve (65). Pilot oil then goes through line (59) to the pump regulator. This causes the main pump to destroke. When a hydraulic control is activated, increased oil pressure in line (41) activates spool (56). This opens the oil flow from the pump regulator to the hydraulic oil tank. The main pump does not move to a destroked position. The main pump provides normal output flow.
When all of the control levers are in the NEUTRAL position, the oil that is in line (41) remains at low pressure and the oil pressure does not activate pressure switch (47). This allows the system for one touch low idle control to activate.
Note: For more information on one touch low idle control, refer to Systems Operation/Testing and Adjusting, "Excavator Electric and Electronic System".
When a swing and/or implement control is operated, the pilot oil pressure in passage (26) increases. The increased oil pressure activates selector valve (15). This allows main relief valve (22) to open at the relief valve pressure setting for implement operation or swing operation. When travel control is activated alone, oil pressure in passage (25) increases. This allows the main relief valve to open at the relief valve pressure setting for travel operation.
Note: For more information on the main relief valve, refer to Systems Operation, "Main Control Valve".
When the travel control valve is operated at the same time as the implement controls, the pilot oil pressure in passage (26) goes through passage (17) to straight travel control valve (18). Straight travel control valve (18) activates so that the machine can travel straight.
Note: For more information, refer to Systems Operation, "Travel System".
Swing Parking Brake Release (Circuit)
The circuit for the swing parking brake release releases the swing parking brake during implement operation and/or swing operation. Pilot oil in passage (36) goes through line (34) and hydraulic activation control valve (20) to the control valve for swing parking brake (4). Pilot oil in passage (26) also goes through line (5 ) to the control valve for swing parking brake (4). When the implement controls and/or swing controls are operated, the pilot oil pressure in passage (26) increases. The pressure increase activates the control valve for swing parking brake (4) to the open position. The pilot oil from line (6) goes through the control valve for swing parking brake (4) to swing parking brake (3). This releases the swing parking brake.
Note: For more information, refer to Systems Operation, "Swing System".
Circuit for Automatic Travel Speed Change Valve
Pilot oil flows from passage (45) to travel speed solenoid valve (44). When the switch for the travel speed is placed in the HIGH SPEED position, travel speed solenoid valve (44) opens. Pilot oil from passage (45) goes through travel speed solenoid valve (44). From the travel speed solenoid valve, oil enters line (13) and passes to left and right travel displacement change valves (1) and (2). Valves (1) and (2) activate and the machine travels in an optimum speed.
Note: For more information, refer to Systems Operation, "Travel System".
Major Components In The Pilot Oil Circuit
 | |
| Illustration 2 | g00420115 |
Schematic for the pilot oil circuit (partial schematic) (1) Pilot control valve (stick and/or swing) (2) Pilot control valve (bucket and/or boom) (3) Accumulator (4) Pilot relief valve (5) Right pump (6) Left pump (7) Pilot pump (8) Hydraulic activation control valve (9) Pilot oil manifold (10) Pilot filter | |