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| Illustration 1 | g00296634 |
Schematic for the Main Hydraulic System (1) Main control valve (2) Auxiliary cylinders (3) Tilt cylinder (4) Lift cylinders (5) Ride control diverter valve (6) Line relief valve for the head end of the auxiliary cylinder (7) Line relief valve for the rod end of the tilt cylinder (8) Line relief valve for the rod end of the auxiliary cylinder (9) Line relief valve for the head end of the tilt cylinder (10) Main relief valve (11) Check valve (12) Auxiliary valve spool (13) Check valve (14) Tilt valve spool (15) Check valve (16) Lift valve spool (17) pilot manifold (18) Ride control relief valve (19) Implement and pilot/brake pump (20) Implement pump (21) Pilot/brake pump (22) Hydraulic oil tank (AA) Pressure tap for auxiliary valve spool (BB) Pressure tap for the auxiliary valve spool (CC) Pressure tap for the tilt valve spool (DD) Pressure tap for the tilt valve spool (EE) Pressure tap for the lift valve spool (FF) Pressure tap for the lift valve spool (GG) Pressure tap for pilot pressure | |
Note: Illustrations 1 and 2 show a machine with an auxiliary function. Machines without an auxiliary function (logging fork, side dump bucket, multipurpose bucket, etc) will not have auxiliary cylinders (2) or the auxiliary components of main control valve (1) .
The main hydraulic system is made up of the following components: main control valve (1), auxiliary cylinders (2), tilt cylinder (3), lift cylinders (4) and implement pump (20) .
Implement pump (20) supplies the high pressure oil that operates auxiliary cylinders (2), tilt cylinder (3), and lift cylinders (4). Oil flows from the implement pump to main control valve (1).
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| Illustration 2 | g00296714 |
Top View of the Valve Group without Implement Lines (Front End Frame) (5) Ride control diverter valve (6) Line relief valve for the head end of the auxiliary cylinder (7) Line relief valve for the rod end of the tilt cylinder (8) Line relief valve for the rod end of the auxiliary cylinder (9) Line relief valve for the head end of the tilt cylinder (10) Main relief valve (12) Auxiliary valve spool (14) Tilt valve spool (16) Lift valve spool (17) pilot manifold (18) Ride control relief valve (AA) Pressure tap for the auxiliary valve spool (BB) Pressure tap for the auxiliary valve spool (CC) Pressure tap for the tilt valve spool (DD) Pressure tap for the tilt valve spool (EE) Pressure tap for the lift valve spool (FF) Pressure tap for the lift valve spool (GG) Pressure tap for the pilot pressure | |
Main relief valve (10) controls the pressure in the main hydraulic system. Main relief valve (10) opens when the oil pressure from the implement pump (20) to the implement cylinders rises above the relief pressure setting.
Pilot oil flows from pilot/brake pump (21) to pilot manifold (17). Pilot oil from pilot manifold (17) causes valve spools (12), (14), and (16) to move when the control levers are moved.
Tilt valve spool (14) has three positions: TILT BACK position, HOLD position and DUMP position. When tilt valve spool (14) moves to the TILT BACK position, high pressure oil flows through the tilt valve spool to the head end of the tilt cylinder. Oil from the rod end of the tilt cylinder flows through the tilt valve spool back to the hydraulic oil tank.
In the HOLD position, all of the oil flow returns to the hydraulic oil tank. When the tilt valve spool moves to the DUMP position, high pressure oil flows through the tilt valve spool to the rod end of the tilt cylinder. Oil from the head end of the tilt cylinder flows through the tilt valve spool back to the hydraulic oil tank.
Lift valve spool (16) has three positions: RAISE position, HOLD position and LOWER position. In the RAISE position, high pressure oil flows to the head end of the lift cylinder. In the HOLD position, all of the oil flow returns to the hydraulic oil tank. In the LOWER position, high pressure oil flows to the rod end of the lift cylinder.
When the lift control lever in the cab is placed in the FLOAT position the lift valve spool remains in the LOWER position. A float valve in the pilot manifold (17) opens in order to allow the bucket to rest on the ground.
The flow of oil through the main control valve changes when the machine has an auxiliary circuit. The oil from implement pump (20) first flows to auxiliary valve spool (12). The auxiliary valve spool has three positions: OPEN position, HOLD position and CLOSE position.
In the OPEN position, high pressure oil flows to the rod end of the lift cylinder. In the HOLD position, all of the oil flow returns to the hydraulic oil tank. In the CLOSE position, high pressure oil flows to the head end of the lift cylinder.
The auxiliary circuit, the tilt circuit, and the lift circuit have check valves that are located inside the main control valve. Check valves (11), (13) and (15) prevent reverse oil flow through the main control valve. Reverse flow through the main control valve could cause cylinder drift.
Line relief valves (6), (7), (8), and (9) maintain the pressure in both the auxiliary circuit and the tilt circuit when valve spools (12) and (14) are in the HOLD position. The line relief valves reduce the possibility of damage to the circuit components when outside forces are put on the bucket or auxiliary attachment. Ride control relief valve (18) relieves the pressure in the lines for the head end of the lift cylinder.