Hold Position
Note: Detailed oil flow is not shown for the HOLD position. Refer to Illustration 1 for references to the components.
When the engine is running, the charge pump (not shown) sends pilot oil to pressure accumulator (19) through line (20). Pilot oil is available to the electrohydraulic pilot solenoids.
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. In the HOLD position, the spring centers the valve spool.
Tilt Back Operation
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| Illustration 1 | g01929177 |
Tilt back operation (7) Bucket tilt control valve (8) Tilt cylinder (9) Line relief valve (tilt rod end) (10) Line relief valve (tilt head end) (19) Accumulator (20) Flow from the charge circuit of the right drive pump (22) Margin relief valve (24) Pilot control solenoid (26) Implement pumps (27) Hydraulic oil tank | |
When the control lever is moved to the TILT BACK position, pilot oil flows to the right end of the tilt valve spool (7). This causes the valve spool to move to the left.
The movement of tilt valve spool (7) causes the load signal pressure to increase. When signal pressure increases the flow at implement pump (26) increases. The oil from implement pump (26) now flows to the head end of tilt cylinder (8). 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.
The oil from the rod end flows into the valve bank. Then, the oil travels to hydraulic tank (27) .
The solenoids divert the flow of pilot oil from tilt valve spool (7) back to tank (27). The spring moves tilt valve spool (7) back into the HOLD position. The pilot oil at the right end of the tilt valve spool flows back through the valve bank to hydraulic tank (27). The implement oil in tilt cylinder (8) 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 2 | g01929179 |
Dump operation (7) Bucket tilt control valve (8) Tilt cylinder (9) Line relief valve (tilt rod end) (10) Line relief valve (tilt head end) (19) Accumulator (20) Flow from the charge circuit of the right drive pump (22) Margin relief valve (24) Pilot control solenoid (26) Implement pumps (27) Hydraulic oil tank | |
When the control lever is moved to the DUMP position, pilot oil flows to the left end of tilt valve spool (7). This causes the valve spool to move to the right.
The movement of the tilt valve spool (7) causes the load signal pressure to increase. When signal pressure increases the flow at implement pump (26) increases. The oil from implement pump (26) now flows to the rod end of tilt cylinder (8). 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.
The oil from the head end flows into the valve bank. Then, the oil travels to hydraulic tank (27) .
When the tilt control lever is released, the lever moves to the HOLD position. The solenoids divert the flow of pilot oil from tilt valve spool (7) back to tank (27). The spring on tilt valve spool (7) moves the valve spool back to the HOLD position. The pilot oil at the left end of the tilt valve spool flows back through the valve bank to hydraulic tank (27) .
The oil in tilt cylinder (8) is held by the tilt valve (7). Then, movement of the cylinder piston and rod stops. The bucket is held in position until the tilt control lever is moved again.