Boom Raise (High Speed)
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| Illustration 1 | g01149232 |
Hydraulic schematic for BOOM RAISE (high speed) (1) Boom cylinders (2) Boom lowering control valve (3) Valve (4) Line (oil flow from boom cylinder rod end) (5) Passage (6) Line (oil flow to boom lowering control valve) (7) Manual ball valve (8) Valve (9) Valve (10) Port (11) Main control valve (12) Pilot line (13) Port (14) Line (15) Pilot control valve (boom) (16) Port (17) Check valve (18) Boom II control valve (19) Spring (20) Boom I control valve (21) Spring (22) Load check valve (23) Return passage (24) Spring (25) Pilot line (26) Parallel feeder passage (27) Return passage (28) Parallel feeder passage (29) Pilot line (30) Pressure reducing valve for boom priority (31) Drive pump (32) Idler pump (33) Pilot pump (34) Return line | |
A BOOM RAISE operation at high speed is accomplished when the oil delivery from both drive pump (31) and idler pump (32) is supplied to the head end of boom cylinders (1) . Boom I control valve (20) and boom II control valve (18) operate during the high speed operation. A BOOM RAISE operation at low speed is accomplished when the oil delivery from only drive pump (31) is supplied to the head end of boom cylinders (1) . During the low speed operation, boom I control valve (20) operates alone.
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| Illustration 2 | g01402557 |
Main control valve compartment (20) Boom I control valve (18) Boom II control valve | |
The oil delivery from drive pump (31) flows through parallel feeder passage (28) in main control valve (11) to boom I control valve (20) . The oil delivery from idler pump (32) flows through parallel feeder passage (26) in main control valve (11) to boom II control valve (18) .
When the joystick for the boom is moved to the full BOOM RAISE position, the pilot oil flows from pilot control valve (15) through pilot line (25) . The pilot oil flow then divides into two flow paths. Part of the pilot oil flows through pilot line (12) to port (10) of main control valve (11) . The remainder of the pilot oil flows through pilot line (12) to port (13) of the main control valve.
A portion of the oil in pilot line (12) also flows through pilot line (29) to pressure reducing valve (30) for boom priority. During a combined operation of BOOM RAISE and STICK IN, the pilot oil flow to pressure reducing valve (30) for boom priority causes the boom circuit to receive oil flow priority. This allows the boom to raise at a high speed.
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| Illustration 3 | g01149535 |
Boom I control valve (BOOM RAISE position) (13) Port (22) Load check valve (24) Spring (27) Return passage (28) Parallel feeder passage (35) Port (36) Passage (37) Port (38) Spool (39) Passage | |
The pilot oil flow from port (13) shifts spool (38) of boom I control valve (20) against the force of spring (24) . The oil delivery from the drive pump in parallel feeder passage (28) flows through load check valve (22) , passage (36) , passage (39) , port (37) , and line (14) to boom lowering control valves (2) . The oil delivery from the drive pump flows through valve (5) to the head end of boom cylinders (1) .
Note: For more information on the boom lowering control valve, refer to Systems Operation, "Boom Lowering Control Valve".
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| Illustration 4 | g01149557 |
Boom II control valve (BOOM RAISE position) (10) Port (16) Port (17) Check valve (19) Spring (26) Parallel feeder passage (40) Passage (41) Spool (42) Passage | |
The pilot oil flow in port (10) of boom II control valve (18) shifts spool (41) against the force of spring (19) . The oil delivery from the idler pump in parallel feeder passage (26) now flows through passage (40) , passage (42) , check valve (17) and flows out of port (16) to line (14) . The oil delivery from the drive pump combines with the oil delivery from the idler pump at the block valve on main control valve (11) . The combined pump oil flows through line (14) and boom lowering control valves (2) to the head end of boom cylinders (1) .
Note: The swing priority valve does not affect the boom II control valve.
Return oil from the rod end of boom cylinders (1) flows through line (4) and port (35) to boom I control valve (20) . The oil then flows through the passage in boom I control valve (20) , return passage (39) , return passage (27) and return line (34) to the hydraulic tank.
Boom Raise (Low Speed)
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 (20) and boom II control valve (18) .
When the boom is raised at a low speed, boom I control valve (20) opens and boom II control valve (18) remains closed. The force of spring (24) in boom I control valve (20) is less than the force of spring (19) in boom II control valve (18) . Because of the low pilot oil pressure, boom I control valve (20) will open and boom II control valve (18) will remain closed.
The oil delivery from drive pump (31) now flows to the head end of boom cylinders (1) . Without the oil delivery from idler pump (29) , the cylinder rod movement slows down when the boom is raised. The low speed operation of the boom is performed.
Boom Priority
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| Illustration 5 | g01149559 |
Hydraulic schematic for BOOM RAISE and STICK OUT (1) Boom cylinders (15) Pilot control valve (boom) (30) Pressure reducing valve for boom priority (43) Stick cylinders (44) Pilot control valve (stick and swing) (45) Stick II control valve (46) Pilot line | |
During combined operations of BOOM RAISE and STICK OUT, the pilot oil pressure from pilot control valve (15) for the boom activates pressure reducing valve (30) for boom priority. Pressure reducing valve (30) for boom priority causes oil flow priority to the head end of boom cylinders (1) during this combined hydraulic operation.
When the joystick for the stick is moved to the STICK OUT position, a portion of the pilot oil from pilot control valve (44) for the stick flows through pressure reducing valve (30) 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 (15) for the boom increases. This gradual increase in pilot oil pressure causes the spool in pressure reducing valve (30) to gradually shift.
A portion of the pilot oil that flows to stick II control valve (45) from pilot control valve (44) for the stick is routed to the hydraulic tank. The pilot oil pressure in pilot line (46) 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 stick cylinders (43) decreases. This 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 (15) for the boom 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 joystick for the boom and boom priority automatically activates when the joystick reaches a certain position during a BOOM RAISE operation.
Boom Lower
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| Illustration 6 | g01150270 |
(1) Boom cylinders (2) Boom lowering control valve (3) Valve (4) Line (oil flow from boom cylinder rod end) (5) Passage (6) Line (oil flow to boom lowering control valve) (7) Manual ball valve (8) Valve (9) Valve (11) Main control valve (15) Pilot control valve (boom) (20) Boom I control valve (22) Load check valve (23) Return passage (25) Pilot line (27) Return passage (28) Parallel feeder passage (31) Drive pump (34) Return line (47) Valve (48) Pilot line (49) Line (50) Center bypass passage (51) Passage (52) Pilot line (53) Port (54) Check valve | |
Introduction
When the boom is lowered, oil from drive pump (22) is supplied to boom cylinders (1) through control valve (20) .
Control valve (20) contains a regeneration circuit for check valve (15) . When the control lever is moved to the BOOM LOWER position, check valve (15) is forced open. Oil from the head end of cylinders (1) flows to the rod end of cylinders (1) . During a boom lower operation, the regeneration circuit shares oil from drive pump (22) with the other implement functions.
Boom Lower
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| Illustration 7 | g01436709 |
Control valve BOOM LOWER (boom I) (22) Load check valve (23) Return passage (28) Parallel feeder passage (50) Center bypass passage (53) Port (54) Check valve (55) Passage (56) Passage (57) Passage (58) Spring (59) Spring chamber (60) Valve (61) Spring (62) Passage (63) Stem (64) Passage (65) Passage (66) Passage (67) Spring (68) Passage (69) Passage | |
When the control lever is moved to the BOOM LOWER position, pilot oil from pilot control valve (L) flows into pilot line (25) . Pilot oil in pilot line (25) flows into two paths. Pilot oil flows from line (48) to boom lowering control valves (2) . The pilot oil shifts valves (9) and (5) . Oil from the head end of boom cylinders (1) now flows to the hydraulic tank through return line (34) .
Pilot oil also flows through line (52) to boom I control valve (20) . The pilot oil causes boom I control valve (20) to shift upward.
When boom I control valve (21) is shifted, the negative flow control pressure in center bypass passage (50) becomes low. The negative flow control pressure is now low. Drive pump (31) upstrokes resulting in maximum flow.
The drive pump oil in parallel feeder passage (28) flows through passage (51) to line (4) . The flow in line (4) enters the rod end of boom cylinders (1) .
The return oil from boom cylinders (1) enters boom lowering control valves (2) . Oil then flows through valves (5) to lines (6) . Return oil in lines (6) enters valve (47) . The oil combines into one flow. The oil then flows through valves (8) and (9) . Part of the return oil flows through line (34) to the hydraulic tank. The rest of the return oil flows through line (14) to boom I control valve (20) . Part of the oil flows through the valve to return passage (27) and to the hydraulic tank.
Because the return oil flow is restricted at passage (57) , movement of the boom cylinder rod is slowed down. This causes the boom to lower at an appropriate speed due to the flow rate from the drive pump.
Regeneration Circuit
The remainder of the return oil in passage (66) flows through passage (62) in spool (63) to check valve (54) . When spool (63) moves to the right, passage (68) is open to return passage (28) . Oil flows from spring chamber (59) to return passage (28) . Because the oil pressure in spring chamber (59) decreases, the oil pressure in passage (62) overcomes the forces of springs (58) and (61) . Valve (60) and check valve (54) move to the left. When both valves are opened the oil in passage (56) is allowed to flow through passage (69) and out of passage (55) . The oil then flows to the rod end of the boom cylinders.
When the boom control lever is moved to the NEUTRAL position, there is no oil supply to port (53) . Spool (63) is shifted to the left neutral position by spring (67) . When passage (65) closes, the oil flow from passage (66) to passage (62) is blocked. Check valve (54) is now closed by the force of spring (61) and valve (60) is moved to the right side by the force of spring (58) .
Negative Flow Control During Activation of Regeneration Circuit
The boom cylinder rod end requires less drive pump oil to be supplied to the cylinder due to the activation of the regeneration circuit for boom lower.
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| Illustration 8 | g01436959 |
Control valve (stick II) (50) Center bypass passage (70) Center bypass passage (71) Stem | |
When the boom control lever is moved to the full BOOM LOWER position, drive pump oil flows through partially open passage (8) . The oil flows from passage (50) through center bypass passage (70) . Because center bypass passage (70) is blocked by control valve (71) , the negative flow control pressure is low and the stroke of drive pump (31) is maximum.
When the boom control lever is partially moved to the BOOM LOWER position, spool (63) is slightly shifted to the right. Passage (56) and passage (60) partially open. This causes passage (57) to close. Return oil in passage (66) flows through passages (60) and (62) to return check valve (22) . Return check valve (22) opens. This allows oil flow through passage (69) and passage (55) .
Drive pump oil in center bypass passage (50) flows through partially open passage (64) . Drive pump oil in passage (64) enters center bypass passage (50) . When stem (70) of stick control valve (71) is moved slightly to the right side, return oil flows into partially open center bypass passage (50) .
With the appropriate opening of center bypass passage (50) , the correct amount of oil is allowed to flow which causes a negative flow control pressure. The negative flow causes the pump to destroke for proper cylinder operation.