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| Illustration 1 | g06015812 |
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Hydraulic schematic for BOOM RAISE (high speed) (1) Boom cylinders (2) Line (oil flow from boom cylinder rod end) (3) Line (oil flow to boom cylinder head end) (4) Line (5) Pilot line (6) Main control valve (7) Port (8) Check valve (9) Boom drift reduction / regeneration valve (10) Pilot line (11) Pilot line (12) Port (13) Spring (14) Line (15) Port (16) Check valve (17) Boom II control valve (18) Pilot control valve (boom and bucket) (19) Return line (20) Spring (21) Load check valve (22) Parallel feeder passage (23) Return passage (24) Parallel feeder passage (25) Return passage (26) Boom I control valve (27) Pilot line (28) Pressure reducing valve for boom priority (29) Drive pump (30) Idler pump (31) Pilot pump | |
A high-speed BOOM RAISE operation is accomplished when oil delivery from both drive pump (29) and idler pump (30) is supplied to the head end of boom cylinders (1). Boom I control valve (26) and boom II control valve (17) operate during the high-speed operation. A BOOM RAISE operation at low speed is accomplished when the oil delivery from only idler pump (30) is supplied to the head end of boom cylinders (1). During the low speed operation, boom I control valve (26) operates alone.
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| Illustration 2 | g01472075 |
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Main control valve compartment (17) Boom II control valve (26) Boom I control valve | |
The oil delivery from idler pump (30) flows through parallel feeder passage (24) in main control valve (6) to boom I control valve (26). The oil delivery from drive pump (29) flows through parallel feeder passage (22) in main control valve (6) to boom II control valve (17).
When the joystick for the boom is moved to the full BOOM RAISE position, the pilot oil flows from pilot control valve (18) through pilot line (10). The pilot oil flow then divides into two flow paths. Part of the pilot oil flows through pilot line (11) to port (12) of main control valve (6). The remainder of the pilot oil flows through pilot line (5) to port (7) of the main control valve.
A portion of the oil in pilot line (5) also flows through pilot line (27) to the pressure reducing valve for boom priority (28). During a combined operation of BOOM RAISE and STICK IN, the pilot oil flow to the pressure reducing valve for boom priority (28) causes the boom circuit to receive oil flow priority. This action allows the boom to raise at a high speed.
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| Illustration 3 | g01457736 |
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Boom I control valve (7) Port (13) Spring (21) Load check valve (24) Parallel feeder passage (25) Return passage (32) Port (33) Passage (34) Passage (35) Passage (36) Port (38) Spool (39) Passage (40) Passage | |
The pilot oil flow from port (7) moves spool (38) of boom I control valve (26) to the left against the force of spring (13). The drive pump oil in parallel feeder passage (24) flows through load check valve (21), and passages (33), (39) and (34). The oil then flows through passage (35) to port (36).
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| Illustration 4 | g02296254 |
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Boom II control valve (12) Port (15) Port (16) Check valve (20) Spring (22) Parallel feeder passage (41) Passage (42) Spool (43) Passage | |
The pilot oil in port (12) of boom II control valve (17) moves spool (42) to the left against the force of spring (20). Idler pump oil from parallel feeder passage (22) now flows through passage (41), passage (43), check valve (16) and flows out of port (15) to line (4).
The oil flow in line (4) then combines with the drive pump oil in port (36). The combined pump oil flows through line (14) to boom drift reduction / regeneration valve (9). The combined pump oil shifts check valve (8) upward. The pump oil then flows through line (3) to the head end of boom cylinders (1).
Return oil from the rod end of boom cylinders (1) flows through line (2) to control valve (26). The oil enters port (32) and flows to passage (40). The oil then flows to return passage (25) and to return line (19) back to the hydraulic tank. The cylinder rods extend and the boom raises.
Reference: For more information regarding boom drift reduction / regeneration valve (9), refer to Systems Operation, "Boom Drift Reduction Valve".
When the joystick for the boom is moved less than half of the travel distance for BOOM RAISE, low pilot oil pressure is supplied to boom I control valve (26) and boom II control valve (17).
When the boom is raised at a low speed, boom I control valve (26) opens and boom II control valve (17) remains closed. The force of spring (13) in boom I control valve (26) is less than the force of spring (20) in boom II control valve (17). Because of the low pilot oil pressure, boom I control valve (26) will open and boom II control valve (17) will remain closed.
The oil delivery from drive pump (29) flows to the head end of boom cylinders (1). Oil delivery from idler pump (30) is not supplied to the head end of boom cylinders (1). Without the oil delivery from idler pump (30), the cylinder movement is slower when the boom is raised. The low speed operation of the boom is performed.
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| Illustration 5 | g06015872 |
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Hydraulic schematic for BOOM RAISE and STICK IN (1) Boom cylinders (18) Pilot control valve (boom and bucket) (28) Pressure reducing valve for boom priority (44) Stick I control valve (45) Stick II control valve (46) Pilot control valve (stick and swing) | |
During combined operations of BOOM RAISE and STICK IN, the pilot oil pressure from pilot control valve (18) activates pressure reducing valve for boom priority (28). Pressure reducing valve for boom priority (28) causes oil flow priority to the head end of the boom cylinders (1) during this combined hydraulic operation. The force required to perform a BOOM RAISE operation is much higher than the force required to perform a STICK IN operation. Without boom priority, the STICK IN operation would move at a higher speed than the BOOM RAISE operation.
When the joystick for the stick is moved to the STICK IN position, pilot oil from pilot control valve (46) flows to stick I control valve (44) and through pressure reducing valve for the boom priority (28) to stick II control valve (45). As the joystick for the boom is moved farther from the NEUTRAL position during a BOOM RAISE operation, pilot oil pressure from pilot control valve (18) increases. This gradual increase in pilot oil pressure causes the spool in pressure reducing valve for the boom priority (28) to shift.
Pilot oil that flows to stick II control valve (45) from pressure reducing valve (28) is routed to the hydraulic tank. The pilot oil pressure that acts on stick II control valve (45) decreases. Stick II control valve (45) shifts toward the NEUTRAL position. The amount of oil flow from the main pumps to the stick hydraulic circuit decreases. This condition causes a greater portion of the oil flow from the main pumps to flow to the head end of the boom cylinders (1).
Since the pilot oil pressure from pilot control valve (18) directly corresponds to the amount of movement or position of the joystick, a gradual change to boom priority occurs. Thus, boom priority is controlled by the position of the boom joystick. Boom priority automatically activates when the joystick reaches a certain position during a BOOM RAISE operation.
Boom Lower (Without Regeneration)
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| Illustration 6 | g06015924 |
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Hydraulic schematic for BOOM LOWER without regeneration (1) Boom cylinders (2) Line (oil flow from boom cylinder rod end) (3) Line (oil flow to boom cylinder head end) (8) Valve (9) Boom drift reduction / regeneration valve (14) Line (18) Pilot control valve (21) Load check valve (24) Parallel feeder passage (25) Return passage (26) Boom I control valve (29) Drive pump (30) Idler pump (31) Pilot pump (47) Port (48) Pilot line | |
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| Illustration 7 | g06015936 |
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Boom drift reduction / regeneration valve partial schematic (1) Boom cylinders (2) Line (oil flow from boom cylinder rod end) (3) Line (oil flow to boom cylinder head end) (8) Check valve (9) Boom drift reduction / regeneration valve (26) Boom I control valve (47) Port (48) Pilot line (49) Passage (50) Spool (51) Return line | |
When the boom is lowered, oil from drive pump (29) is supplied to the head end of boom cylinders (1) through control valve (26). The boom II control valve is not used during a BOOM LOWER operation.
When the joystick for the boom is moved to the BOOM LOWER position, pilot oil pressure from pilot control valve (18) flows to port (47). Pilot oil pressure shifts control valve (26). Pilot oil pressure in port (47) also flows through line (48) to boom drift reduction / regeneration valve (9). The pilot oil pressure in valve (9) shifts spool (50) to the left. Passage (49) is open to drain line (51).
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| Illustration 8 | g02309233 |
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Boom I control valve (13) Spring (21) Load check valve (24) Parallel feeder passage (25) Return passage (32) Port (33) Passage (36) Port (38) Spool (39) Passage (40) Passage (47) Port | |
The pilot oil flow from port (47) shifts spool (38) in control valve (26) against the force of spring (13). The oil delivery from the drive pump in parallel feeder passage (24) flows through load check valve (21), passage (33), passage (40) and port (32). The oil delivery from the drive pump then flows through line (2) to the rod end of boom cylinders (1).
Return oil flow from the head end of boom cylinder (1) flows through line (3) to boom drift reduction / regeneration valve (9). Since spool (51) is shifted to the left by pilot pressure from pilot line (48), return oil in line (3) forces check valve (8) to open. Return oil then flows to line (14) and to port (36) of control valve (26). The return oil flows from port (36) to passage (39) and to return passage (25). Oil flows from return passage (25) to the return hydraulic system. The boom lowers.
Boom Lower (With Regeneration)
When the boom is lowered and the work tool is not touching the ground, the boom hydraulic system will regenerate. The mass of the boom, stick, and work tool cause the head end of the boom cylinders to be pressurized. The pressure in the head end of the boom cylinders is higher than the pump output in the rod end of the boom cylinders.
Because the pressure in the head end of the boom cylinders is higher than the rod end, the excessive pressure is cycled back to the rod end of the cylinders. Cycling the pressure oil back to the rod end of the boom cylinders reduces the load on the main pumps. Regeneration also prevents cavitation conditions in the rod end of the boom cylinders.
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| Illustration 9 | g06015988 |
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Hydraulic schematic for BOOM LOWER with regeneration (1) Boom cylinders (2) Line (oil flow from boom cylinder rod end) (3) Line (oil flow to boom cylinder head end) (8) Valve (9) Boom drift reduction / regeneration valve (14) Line (18) Pilot control valve (25) Return passage (26) Boom I control valve (29) Drive pump (30) Idler pump (31) Pilot pump (47) Port (48) Pilot line | |
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| Illustration 10 | g06015994 |
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Boom drift reduction / regeneration valve partial schematic (1) Boom cylinders (2) Line (oil flow from boom cylinder rod end) (3) Line (oil flow to boom cylinder head end) (8) Check valve (9) Boom drift reduction / regeneration valve (14) Line (26) Boom I control valve (47) Port (48) Pilot line (49) Passage (50) Spool (51) Return line (52) Pressure sensor (53) Line (54) Check valve (55) Passage (56) Proportional reducing valve (57) Orifice (58) Pressure sensor | |
Pressure sensor (52) in line (3) sends an electrical signal to the machine ECM. Pressure sensor (58) in pilot line (48) sends an electrical signal to the machine ECM as well. The machine ECM uses the inputs from sensor (52) and sensor (58) to determine the electrical signal needed for proportional reducing valve (56). The electrical signal sent from the machine ECM is variable. Proportional reducing valve (56) controls the pilot oil pressure that shifts spool (50). Full pilot oil pressure from pilot line (48) flows to spool (50) when the machine ECM DE-ENERGIZES valve (56). When the machine ECM ENERGIZES valve (56), a reduced pilot oil pressure from pilot line (48) flows to spool (50).
The machine ECM energizes proportional reducing valve for boom regeneration (56) to throttle the rate of regeneration during a BOOM LOWER operation. With a low electrical signal, the boom lowers fast. With a high electrical signal, the boom lowers slow. The rate of speed of the BOOM LOWER operation during regeneration is related to the amount of joystick movement.
The BOOM LOWER with regeneration operation is like the BOOM LOWER without regeneration operation.
When the joystick for the boom is operated, pilot pressure from pilot control valve (18) flows to port (47) at boom I control valve (26). Pilot oil pressure shifts control valve (26) upward. Pilot oil pressure also flows through line (48) to boom drift reduction / regeneration valve (9). Pilot oil pressure shifts spool (50) to the left. The oil in the spring cavity of check valve (8) flows through passage (49) and spool (50) to return line (51).
Oil from the boom cylinder head end in line (3) shifts check valve (8) upward. The oil now flows to line (14) and passage (55).
Orifice (57) restricts the flow of oil in line (14) to the return system. The restriction of orifice (57) causes the return oil from the boom cylinder head end to increase. The higher pressure oil then flows through passage (55) and spool (50) to check valve (54). The oil in passage (55) opens check valve (54). The oil then flows through line (53) to line (2). The oil in the head end of the boom cylinders flows to the rod end of the boom cylinders.
Oil that is not needed to cycle from the head end of the boom cylinders to the rod end of the boom cylinders flows to return passage (25). The oil in return passage (25) then flows to the return hydraulic system and the hydraulic tank. The boom cylinder rods retract and the boom lowers.
Note: Once the work tool is on the ground, regeneration is no longer needed. Back pressure is no longer created by the mass of the implements in the head end of the boom cylinders. The pressure in passage (55) is less than the pressure in line (53). Check valve (54) closes. Check valve (54) prevents the higher pressure in passage (53) from flowing to passage (55). The oil in the head end of boom cylinders (1) returns to boom I control valve (26) and to return passage (25). The pump output pressure is used to retract the boom cylinders.