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| Illustration 1 | g06302941 |
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(1) Tilt solenoid (rack)
(2) Tilt cylinder (rod end) relief valve (3) Main control valve relief (4) Tilt cylinder check valve (5) Tilt cylinder (head end) relief valve (6) Tilt solenoid (dump) (7) Lift solenoid (raise) (8) Lift cylinder (head end) relief valve (9) Pilot ON/OFF solenoid (10) Lift cylinder check valve (11) Float solenoid (12) Pressure reducing valve (13) Lift cylinder (rod end) relief valve (14) Lift solenoid (lower) | |
The main hydraulic valve is located in the non-engine end frame. The standard main control valve is equipped with two stems. One stem controls the lift function of the machine. The other stem controls the tilt operation of the machine. The main control valve is open centered. Supply oil flows through the valve and back to the hydraulic tank. As one of the stems is shifted, the supply oil through the main control valve is blocked and the supply oil flows by the main control valve past the load check valve to the appropriate stem. The stem that is shifted will direct the supply oil to the appropriate cylinder work port. If the pressure of the supply oil exceeds the adjusted pressure of main relief valve (3), the valve opens, venting the excess pressure back to the hydraulic tank.
Reference: For additional information about the main relief valve, refer to the Service Manual module Systems Operation, "Relief Valve" for the machine that is being serviced.
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| Illustration 2 | g06306527 |
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Lift function in the HOLD position (1) Tilt solenoid (rack) (2) Tilt cylinder (rod end) relief valve (4) Tilt cylinder check valve (5) Tilt cylinder (head end) relief valve (6) Tilt solenoid (dump) (7) Lift solenoid (raise) (8) Lift cylinder (head end) relief valve (10) Lift cylinder check valve (13) Lift cylinder (rod end) relief valve (14) Lift solenoid (lower) (15) Lift Cylinder rod end (16) Lift cylinder head end (17) Stem (lift) (18) Tank port (19) Passage to the hydraulic tank (20) Passage for the supply oil (21) Internal passage (22) Tank port (AA) Supply oil (BB) Pilot oil (CC) Blocked oil (DD) Tank oil (EE) Active components (FF) Surface area | |
The main control valve is electro-hydraulic and controlled by the pilot system. The valve controls the position of the lift cylinders and the tilt cylinders. The lift valve is equipped with a line relief valve (8) for the head end of the lift cylinders. The lift valve is equipped with a line relief and makeup valve (13) for the rod end of the lift cylinders. Line relief valves protect components of the hydraulic circuit by relieving high pressure. External loads on the bucket or load arms may cause these high pressures. The lift valve has the following positions: RAISE, HOLD and LOWER. Load check valve (10) prevents implement drift when the control valve is initially shifted.
In the HOLD position, pilot oil pressure is present at both ends of the stem (17). The pilot oil and the centering springs keep the stem in the centered position. Stem (17) blocks oil flow to the lift cylinders. Also, oil flow from the cylinders is blocked by the stem. The oil is trapped and the cylinders will remain in the HOLD position.
Oil from the implement pump enters the passage for the supply oil (20), flows around stem (17) and flows through passage (19) to the hydraulic tank.
The flow of oil to the stem (tilt) is similar to the flow of oil to stem (17). Oil from the implement pump enters supply passage (20) and flows around the stem through the passage to the hydraulic tank. With the flow of supply oil through the section for the tilt function before the section for the lift function, the section for the tilt function has priority over the section for the lift function.
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| Illustration 3 | g06306462 |
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Lift function in the LOWER position (1) Tilt solenoid (rack) (2) Tilt cylinder (rod end) relief valve (4) Tilt cylinder check valve (5) Tilt cylinder (head end) relief valve (6) Tilt solenoid (dump) (7) Lift solenoid (raise) (8) Lift cylinder (head end) relief valve (10) Lift cylinder check valve (13) Lift cylinder (rod end) relief valve (14) Lift solenoid (lower) (15) Lift Cylinder rod end (16) Lift cylinder head end (17) Stem (lift) (18) Tank port (19) Passage to the hydraulic tank (20) Passage for the supply oil (21) Internal passage (22) Tank port (AA) Supply oil (BB) Pilot oil (DD) Tank oil (EE) Active components (FF) Surface area (GG) Head end pressure (HH) Reduced pilot pressure | |
When the operator moves the lift lever to the LOWER position, the lift lever sensor sends a PWM signal to the ECM. The ECM analyzes the signals from the following components: lift lever position sensor, lift linkage position sensor and tilt linkage position sensor. The ECM then sends a proportional amount of current to the solenoid (7) for lowering.
Solenoid (7) moves the spool for pilot control actuator (12) in order to drain pilot oil at the right end of stem (17) to tank port (22). This condition reduces the pilot oil pressure at the right end of the stem. The pilot oil pressure on the left end of the stem, shifts the stem to the right.
The stem also directs supply oil from the implement pump to the rod end of the lift cylinders. Supply oil flows past load check valve (10) and around the stem, to the rod end of the lift cylinders. When the stem is shifted to the LOWER position, passage (22) is open for the oil in head end (16) to flow to the hydraulic tank.
Reference: For additional information about the operation of the float function, refer to the section for the Float Position in the service Manual module Systems Operation, "Hydraulic System Operation".
The operation of the RAISE/ RACK BACK function are similar. In the RAISE/ RACK BACK function, pilot oil will shift stem (17) to the left. Supply oil also flows through the passage (20) to the supply passage for the tilt control valve. The section for the tilt control is similar to the section for the lift control.