H Y D R A U L I C S Y S T E MTM 5-3805-258-24-1S Y S T E M S O P E R A T I O Nopen center valve with two valve spools: one forbucket lift and lower, and one for bucket tilt backand dump. The oil from the pilot system causesmovement of the valve spools. When the valvespools are in HOLD position, the oil goes throughlift and tilt control valve (7) and back to the hy-draulic tank.The tilt valve spool has three positions: TILTBACK, HOLD and DUMP. When moved to anoperating position, the tilt valve spool sends oil totilt cylinder (4). The lift valve spool has four posi-tions: RAISE, HOLD, LOWER and FLOAT.When moved to an operating position, the lift valvespool sends oil to lift cylinder (6). The implementsection oil goes first to the tilt valve spool and thento the lift valve spool. When the tilt valve spool isfully in TILT BACK or DUMP position, no pres-sure oil goes to the lift valve spool and the lift cir-cuit will not operate. Both lift and tilt circuits haveload check valves. Make-up valves are in the tiltand lift rod end cylinder lines. The make-up valvefor the rod end of the lift cylinders is a vented valve.The lower stem of lift and tilt pilot valve (3) releases(vents) pressure in the spring passage of the rodend lift make-up valve to provide the FLOAT oper-ation. Main pressure relief valve (16) is in the im-plement oil system before the tilt valve spool. Tiltcylinder relief valves (17) and (18) are in both rodend and head end lines. All of the load check valves,make-up valves and relief valves are part of liftand tilt control valve (7).R I G H T S I D E O F M A C H I N E5. Hydraulic tank. 19. Oil filters.The flow of oil from the implement pump sectionchanges when the machine has an attachment(three spool) control valve. The attachment controlvalve has a lift valve spool, a tilt valve spool andan attachment (third) valve spool. The operationof this valve is very similar to lift and tilt controlvalve (7). The pilot system oil from an attachment(third) pilot valve causes movement of the attach-ment valve spool. This valve spool is also an opencenter type so that when all three valve spools arein HOLD position, the oil goes through the attach-ment control valve and back to the tank.The attachment valve spool has three positions:OPEN or RAISE, HOLD and CLOSE or LOWER.When moved to an operating position, the valvespool sends oil to the attachment cylinder(s). Theimplement section oil now goes first to the attach-ment valve spool before it gets to the tilt valve spool.When the attachment valve spool is fully in CLOSEor LOWER position, the tilt and lift circuits canstill operate. In this position, oil from the rod endof the attachment cylinder(s) goes to the tilt andlift valve spools. The shuttle valve and sequencevalve in the attachment circuit let the lift and tiltcircuits operate during CLOSE or LOWER opera-tion. When the attachment valve spool is fully inOPEN or RAISE position, no pressure oil goes tothe tilt valve spool and the tilt and lift circuits willnot operate. The attachment circuit has a loadcheck valve. In this attachment control valve, mainrelief valve (16) is moved (relocated) so that it isbefore the attachment valve spool in the system.Attachment relief valves are in both rod end andhead end lines. These valves are also part of theattachment control valve.In operation with the tilt hydraulic circuit is thebucket positioner (tilt kickout). It consists of tiltdetent lever (12), a roller and linkage, bucket posi-tioner solenoid (15), a magnet and bucket positionerswitch (20). The bucket positioner moves tilt con-trol lever (9) from the detent [on lever (12)] in TILTBACK position to the HOLD position. This hap-pens as the bucket moves from dump to tilt backwhen it gets to the correct digging angle.F R O N T O F T I L T C Y L I N D E R20. Bucket positioner switch.3-91
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