Hydraulic Schematic Of Main Control Valve
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| Illustration 1 | g06362523 |
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(1) Main pump pressure sensor
(2) Control valve (If Equipped) - VA Boom, XTC, or Angle Blade (3) Control valve (If Equipped) - Angle Blade or AUX 2 (4) Aux 1 control valve (5) Line relief valve - "Port A" (6) Line relief valve - "Port B" (7) Stick control valve (8) Line relief valve (stick cylinder head end) (9) Line relief valve (stick cylinder rod end) (10) Bucket control valve (11) Line relief valve (bucket cylinder rod end) (12) Line relief valve (bucket cylinder head end) (13) Calibration pressure sensor (14) Pilot accumulator (15) Bypass spool (16) Pressure reducing valve (17) Boom load lowering control valve (18) Line relief valve (boom cylinder rod end) (19) Line relief valve (boom cylinder head end) (20) Boom control valve (21) Return line (22) Return line (23) Return line (24) Boom load lowering control valve solenoid (25) Hydraulic oil tank (26) Suction line (27) Main hydraulic pump (28) Supply line (29) Swing control valve (30) Line relief valve (31) Line relief valve (32) Aux 2 control valve (if equipped: boom swing/power offset boom) (33) Line relief valve (34) Blade control valve (35) Right travel control valve (36) Left travel control valve (37) Main control valve (38) Hydraulic lockout solenoid (39) Bypass solenoid | |
Main control valve (37) is located in the hydraulic system between the hydraulic pump and actuators (cylinders and motors). Depending on the machine operation, components and passages in the valves control oil flow and pressure in the circuits from main pump (27). This flow allows the actuators to operate at optimum speed and in the correct direction. These functions also limit the pressure within the hydraulic system.
Main control valve (37) has one distinct path of supply oil.
- The following control valves are in parallel in main control valve (37).
- Control valve (2) (if equipped) - VA Boom, XTC, or Angle Blade
- Control valve (3) (if equipped) - Angle Blade or AUX 2
- Auxiliary 1 control valve (4)
- Stick control valve (7)
- Bucket control valve (10)
- Boom control valve (20)
- Swing control valve (29)
- Auxiliary 2 control valve (32) - (if equipped: boom swing/power offset boom)
- Right travel control valve (35)
- Left travel control valve (36)
The following components are also installed in main control valve (37).
- Line relief valves
- Line relief valve for the head end of the stick cylinder (8)
- Line relief valve for the rod end of the stick cylinder (9)
- Line relief valve for the rod end of the bucket cylinder (11)
- Line relief valve for the head end of the bucket cylinder (12)
- Line relief valve for the rod end of the boom cylinder (18)
- Line relief valve for the head end of the boom cylinder (19)
Additional relief valves may be present for the VA Boom and Auxiliary circuits if equipped.
The main pump oil is delivered through supply line (28) and leaves through return port (T) to hydraulic tank (25).
The following four configurations are the functions of the main control valve.
- Main control valve (37) is in the NEUTRAL position. No load is placed on cylinders and motors.
- Individual valve operation.
- Prevention of cylinder drift with the load check valve.
- Limit the circuit pressure with the relief valve operation.
The description of some components that are installed on or in main control valve (37) will be listed separately. Refer to the appropriate sections that are in this module for further information on the components.
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| Illustration 2 | g06363820 |
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Main control valve (right-rear view) (1) Pilot pressure test port (2) Drain port (3) End cover (4) Valve section for Variable Angle Boom/XTC/Angle Blade (if equipped) (5) Valve section for Angle Blade/AUX 2 (if equipped) (6) Swing Brake solenoid (7) Travel Speed Change solenoid (8) Swing brake control pressure port (9) Travel speed control pressure port (10) Pump Inlet | |
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| Illustration 3 | g06363829 |
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Main control valve (left-front view) (11) Pump pressure sensor (12) SOS port (13) Left travel pressure sensor (14) Right travel pressure sensor (15) Pilot pressure reducing valve (PRV) (16) Back pressure check valve (17) Cooler bypass check valve (18) Calibration pressure sensor (19) Pilot oil accumulator | |
Main Control Valve Operation In Neutral Position
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| Illustration 4 | g06365011 |
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Main control valve (neutral position) (1) Main control valve (2) Main pump pressure sensor (3) Aux 1 control valve (4) Stick control valve (5) Bucket control valve (6) Hydraulic lockout solenoid (7) Bypass solenoid (8) Calibration pressure sensor (9) Pilot accumulator (10) Hydraulic oil cooler bypass valve (11) Bypass spool (12) Pressure reducing valve (13) Boom load lowering control valve (14) Boom control valve (15) Return line (16) Return line (17) Return line (18) Hydraulic oil tank (19) Suction line (20) Main hydraulic pump (21) Supply line (22) Swing control valve (23) Aux 2 control valve (if equipped: boom swing/power offset boom) (24) Blade control valve (25) Right travel control valve (26) Left travel control valve | |
When the control levers are in the NEUTRAL position, oil from main pump (20) enters main control valve (1) through supply line (21). Supply oil divides into two distinct paths. Oil flows through the parallel feeder passage to bypass spool (11) and to pilot pressure reducing valve (12). Oil enters bypass spool (11) and flows through cooler bypass valve (10), return line (16), and back to hydraulic oil tank (18). The other path the oil flows is, through pilot pressure reducing valve (12), through the entire pilot loop, through boom load lowering control valve (13), bypass spool (11). Oil then flows through the return passages of the main control valve, through return line (15), and back to hydraulic oil tank (18).
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| Illustration 5 | g06285550 |
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Bucket control valve (neutral position) (10) Line relief valve (bucket cylinder head end) (11) Line relief valve (bucket cylinder rod end) (12) Bucket control valve (21) Return passage (23) Center bypass passage (36) Port (37) Passage (38) Port (39) Passage (40) Passage (41) Spring (42) Passage (43) Load check valve (44) Passage (45) Spring (46) Passage (47) Pilot line (48) Pilot control solenoid (BUCKET OPEN) (49) Pilot control solenoid (BUCKET CLOSE) (50) Pilot line (51) Passage (52) Bucket control valve spool (53) Passage (54) Passage | |
Bucket control valve (12) is used as a typical example for describing the operation of individual control valves.
When all pilot control solenoids are in the NEUTRAL position, pilot oil does not flow to pilot lines (47) and (50) from the pilot control solenoids. Bucket control valve spool (52) is centered in the NEUTRAL position by the force of springs (41) and (45). The pilot oil flows through center bypass passage (23) and passage (21) back to the hydraulic tank.
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| Illustration 6 | g06285549 |
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Bucket control valve (DUMP position) (10) Line relief valve (bucket cylinder head end) (11) Line relief valve (bucket cylinder rod end) (12) Bucket control valve (21) Return passage (23) Center bypass passage (36) Port (37) Passage (38) Port (39) Passage (40) Passage (41) Spring (42) Passage (43) Load check valve (44) Passage (45) Spring (46) Passage (47) Pilot line (48) Pilot control solenoid (BUCKET OPEN) (49) Pilot control solenoid (BUCKET CLOSE) (50) Pilot line (51) Passage (52) Bucket control valve spool (53) Passage (54) Passage | |
When bucket control valve (12) is moved to the OPEN position, pilot oil is supplied to pilot line (47). Bucket control valve spool (52) moves down. Main oil pressure at passage (44) flows through load check valve (43), bucket control valve spool (52), passage (54), and port (38) to the rod end of the bucket cylinder. Oil in passage (54) divides to passage (39) and to line relief valve (11). Return oil flows through passage (53) and through bucket control valve spool (52). The return oil then flows into passage (42), through passage (40), and into hydraulic tank (33). When hydraulic pressure within passage (39) overcomes the setting for line relief valve (11), oil flows through line relief valve (11), passage (40) and back to hydraulic tank (33).