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| Illustration 1 | g03583668 |
(1) Pilot control valve (boom and bucket) (2) Bucket cylinder (3) Line (4) Line (5) Main control valve (6) Negative flow control orifice (7) Return line (8) Negative flow control line (9) Pilot line (10) Spring (11) Orifice (12) Spring (13) Pilot line (14) Load check valve (15) Bucket control valve (16) Return passage (17) Parallel feeder passage (18) Center bypass passage (19) Center bypass passage (20) Pilot oil manifold (21) Drive pump (22) Idler pump (23) Pilot pump | |
The oil delivery for the bucket hydraulic circuit is supplied by drive pump (21) only.
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| Illustration 2 | g02174427 |
(15) Bucket control valve | |
The oil delivery from drive pump (21) flows through center bypass passage (19) in main control valve (5) to bucket control valve (15) . The oil delivery from idler pump (22) flows through center bypass passage (18) in main control valve (5) . Illustration shows the main control valve when only the bucket hydraulic circuit is activated.
When the hydraulic activation control lever is in the UNLOCKED position, the oil delivery from pilot pump (23) flows through pilot oil manifold (20) to pilot control valve (1) . When the joystick is moved to the BUCKET CLOSE position, pilot oil flows through pilot control valve (1) and pilot line (9) to bucket control valve (15) . The pilot oil pressure shifts the spool in the bucket control valve against spring (12) . The pilot oil on the other end of the spool in the bucket control valve flows through pilot line (13) and pilot control valve (1) . The pilot oil then returns to the hydraulic tank.
Since the spool in the bucket control valve is fully shifted, center bypass passage (19) is blocked. None of the oil delivery from the drive pump flows to negative flow control orifice (6) and no negative flow control pressure is created in center bypass passage (19) . Since no negative flow control pressure is sent through negative flow control line (8) to the drive pump regulator, the drive pump regulator moves the swashplate of the drive pump toward the maximum angle position. The output flow rate of the drive pump is increased and flows through parallel feeder passage (17) . The oil then flows through load check valve (14) , and bucket control valve (15) . From bucket control valve (15) the oil flows through line (4) to the head end of bucket cylinder (2) .
Since the oil delivery for the bucket hydraulic circuit is supplied by the drive pump only, the negative control pressure in center bypass passage (18) is high. Idler pump (22) remains at the destroked position.
ReferenceFor more information concerning the negative flow control operation, refer to Systems Operation, "Negative Flow Control System".
The return oil from the rod end of the bucket cylinder flows through line (3) and orifice (11) in bucket control valve (15) . The oil then returns through return passage (16) , return line (7) and to the hydraulic tank. Orifice (11) restricts the return oil from the rod end of the bucket cylinder.
The BUCKET OPEN operation is like the BUCKET CLOSE operation.
When the joystick is moved to the BUCKET OPEN position, pilot oil flows from pilot control valve (1) to pilot line (13) . From pilot line (13) the pilot oil flows to the bucket control valve. The spool in the bucket control valve shifts against the force of spring (10) . The oil delivery from the drive pump now flows to the rod end of the bucket cylinder.
When the joystick is in the NEUTRAL position, springs (10) and (12) maintain the spool in the bucket control valve in the NEUTRAL position. The oil flow from the head end and the rod end of the bucket cylinder is blocked.