Color Code
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| Illustration 1 | g01052531 |
(AA) Mechanical connection (BB) Cutaway section (CC) Surface color (DD) No pressure (EE) Pneumatic pressure (FF) Activated components (GG) Tank pressure (HH) Lubricating oil (JJ) High pressure (KK) First pressure reduction (LL) Second pressure reduction (MM) Third pressure reduction (NN) Secondary source oil pressure (PP) Charge pressure or pilot pressure (QQ) Reduced charge pressure or pilot pressure (RR) Second reduction of charge pressure or pilot pressure (SS) Trapped oil | |
Hold Position
Note: Detailed oil flow is not shown for the hold position. Refer to Illustration 2 for references to components.
When the engine is running, the charge pump (not shown) sends oil to pressure accumulator (5) through line (C). Pilot oil flows to attachment pilot valve (4) and lift and tilt pilot valve (3). When the control levers are in the HOLD position, the valve stems in the pilot valve block the flow of pilot oil.
In the HOLD position, the passages between the pilot valves and the control valves are open to the hydraulic tank. When there is no oil pressure in the passages, the springs on the valve spools center the valve spools to the HOLD position.
At the same time, implement pump (8) sends oil to main relief valve (7) and to the control valves. The main relief valve controls the maximum pressure in the implement hydraulic system. When all the control valve spools are in the HOLD position, the oil flows through attachment control valve (16) and lift and tilt control valve (1). The oil is sent to the oil filter and hydraulic tank (9) .
The valve spools in the HOLD position block the passages to the rod end and to the head end of the hydraulic cylinders. The oil is trapped and the implements do not move.
Tilt Back Operation
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| Illustration 2 | g01048320 |
Tilt Circuit Attachment spool: HOLD Tilt spool: TILT BACK Lift spool: HOLD (1) Lift and tilt control valve (2) Lift valve spool (3) Lift and tilt pilot valve (4) Attachment pilot valve (5) Accumulator (6) Check valve (7) Main relief valve (8) Hydraulic implement pump (9) Hydraulic tank (10) Bypass valve with screen (hydraulic oil filter) (11) Hydraulic oil cooler (12) Bypass valve (hydraulic oil cooler) (13) Vacuum relief valve (14) Hydraulic oil filters (15) Load check valve for attachment circuit (16) Attachment valve spool (17) Ripper cylinders (attachment) (18) Multipurpose bucket cylinders (attachment) (19) Diverter valve (20) Relief valve for head end and rod end of attachment cylinders (21) Load check valve for tilt circuit (22) Tilt valve spool (23) Choke (24) Tilt cylinder (25) Makeup valve for tilt cylinder (26) Dual setting relief valve for rod end of tilt cylinder (27) Relief valve for head end of the tilt cylinder (28) Load check valve for lift circuit (29) Lift cylinders (30) Makeup valve for lift cylinders (31) Relief valve for head end of lift cylinders (A) Line from charge relief valve (B) Drain line from ECM manifold (C) Line from charge filter (D) Suction line for the charge pumps (E) Line from case drain filter (FF) Activated components (GG) Tank pressure (JJ) High pressure (PP) Charge or pilot pressure (SS) Trapped oil | |
When the pilot control lever is moved to the TILT BACK position, pilot oil flows to the left end of the tilt valve spool (22). This causes the valve spool to move to the right.
The movement of tilt valve spool (22) stops the flow of oil through lift and tilt control valve (1). The pressure at implement pump (8) increases. This opens load check valve (21). The oil from implement pump (8) now flows to the head end of tilt cylinder (24). This causes the cylinder piston and rod to extend.
The Z-bar linkage causes the bucket to tilt back. The movement of the cylinder piston and rod pushes the oil out of the rod end of the tilt cylinder. Choke (23) prevents the bucket from dumping too rapidly. In certain operations, this can be caused by pockets of vapor in the tilt cylinder. Vapor can enter the cylinder from the force against the bucket when the bucket is lowered to the ground during the rotation from the dump position.
The oil flows into lift and tilt control valve (1). The oil travels to the oil filter and hydraulic tank (9) .
There is a detent coil in the TILT BACK lever position. The detent coil holds the tilt control lever in the TILT BACK position until the bucket gets to the correct angle for digging. When the bucket gets to the correct angle, the bucket positioner switch opens. The coil is de-energized and the tilt control lever returns to the HOLD position. The flow of pilot oil through lift and tilt pilot valve (3) is stopped. The springs move the tilt valve spool (22) back into the HOLD position. The pilot oil at the left end of the tilt valve spool flows back through lift and tilt pilot valve (3) to hydraulic tank (9). The implement oil in tilt cylinder (24) is blocked by the tilt valve spool. Movement of the cylinder piston and rod stops. The bucket stays at the correct angle for digging until the tilt control lever is moved. The control lever must be held in the TILT BACK position in order to move the bucket farther.
Dump Operation
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| Illustration 3 | g01048340 |
Dump Curcuit Attachment spool: HOLD Tilt spool: DUMP Lift spool: HOLD (1) Lift and tilt control valve (2) Lift valve spool (3) Lift and tilt pilot valve (4) Attachment pilot valve (5) Accumulator (6) Check valve (7) Main relief valve (8) Hydraulic implement pump (9) Hydraulic tank (10) Bypass valve with screen (hydraulic oil filter) (11) Hydraulic oil cooler (12) Bypass valve (hydraulic oil cooler) (13) Vacuum relief valve (14) Hydraulic oil filters (15) Load check valve for attachment circuit (16) Attachment valve spool (17) Ripper cylinders (attachment) (18) Multipurpose bucket cylinders (attachment) (19) Diverter valve (20) Relief valve for head end and rod end of attachment cylinders (21) Load check valve for tilt circuit (22) Tilt valve spool (23) Choke (24) Tilt cylinder (25) Makeup valve for tilt cylinder (26) Dual setting relief valve for rod end of tilt cylinder (27) Relief valve for head end of the tilt cylinder (28) Load check valve for lift circuit (29) Lift cylinders (30) Makeup valve for lift cylinders (31) Relief valve for head end of lift cylinders (FF) Activated components (GG) Tank pressure (JJ) High pressure (MM) Third pressure reduction (PP) Charge or pilot pressure (SS) Trapped oil | |
When the pilot control lever is moved to the DUMP position, pilot oil flows to the right end of tilt valve spool (22). This causes the valve spool to move to the left.
The movement of the tilt valve spool (22) stops the flow of oil through lift and tilt control valve (1). The pressure at implement pump (8) increases. This opens load check valve (21). The oil from implement pump (8) now flows to the rod end of tilt cylinder (24). This causes the cylinder piston and rod to retract.
The Z-bar linkage causes the bucket to dump. The movement of the cylinder piston and rod pushes the oil out of the head end of the tilt cylinder. Then, the oil flows back through tilt valve spool (22) to lift valve spool (2). When the bucket is dumping, the return oil from the head end of the tilt cylinder is available to lift valve spool (2). Therefore, the operator can LIFT the bucket and the operator can DUMP the bucket simultaneously.
When the tilt control lever is released, the lever moves to the HOLD position. The flow of pilot oil through lift and tilt pilot valve (3) is stopped. The springs on the tilt valve spool (22) move the valve spool back to the HOLD position. The pilot oil at the right end of the tilt valve spool flows back through lift and tilt pilot valve (3) to hydraulic tank (9) .
The oil in tilt cylinder (24) is held by the tilt valve (22). Then, movement of the cylinder piston and rod stops. The bucket is held in position until the tilt control lever is moved again.