ENGINE AR-CORE 3505507 - Caterpillar

Illustration 1 g03499541
(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.
Illustration 2 g03500738
(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 1 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 for the bucket 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) 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). 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 towards the maximum angle position. The output flow rate of the drive pump is increased and flows through parallel feeder passage (17). Drive pump oil flows to load check valve (14), and bucket control valve (15). Drive pump oil also flows to 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.Reference: For 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). From the bucket control valve the return oil flows to return passage (16) and return line (7) 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 flow from pilot control valve (1) flows through pilot