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| Illustration 1 | g00851877 |
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Steering Control Valve in the Neutral Position (1) Pressure regulating valve. (2) Inlet from pump. (3) Outlet to hydraulic tank. (4) Pilot port. (5) Spool. (6) Cylinder crossover relief valve. (7) Shuttle valve. (8) Springs. (9) Retainer. (10) Pilot port. (11) Return passage. (12) Port for right turn. (13) Oil supply passage. (14) Port for left turn. (15) Return passage. (16) Relief valve. | |
Note: This valve does not include secondary steering. Secondary steering will be covered later.
While the engine is running, oil flows from the steering hydraulic tank to the steering pump. The oil flows to the steering control valve through inlet port (2).
The flow of pilot oil to the spool is stopped when the STIC is moved to the center position. The flow of pilot oil is also stopped if a neutralizer valve is activated. When no pilot oil is acting on either end of the spool, centering springs (8) return the spool to the neutral position. As the spool returns to neutral, the pilot oil that had been acting on an end of the spool is forced across an orifice and back to the tank.
Oil flow to port (2) is blocked at passage (13), when the spool is in the center position. Oil in the steering cylinder lines is also blocked in ports (12) and (14). The load for the cylinder is sensed by shuttle valve (7). The shuttle valve routes the signal back to the steering pump. This will cause the pump to destroke. During destroke, the pressure compensator will supply only enough oil for leakage.
Note: If you are making a turn and if you release the lever, the machine will continue to turn. Therefore, releasing the lever will not return the machine to the straight forward travel.
If the fan drive pump fails, pilot oil in the steering pilot system will flow from a port near pressure reducing valve (1) and to the pilot control valve. The pressure reducing valve maintains pilot pressure at
When the operator moves the control lever to turn left, pilot oil will flow from the pilot control valve, through the right neutralizer valve, and through dual check valves into port (10). The pilot oil is forced on retainer (9). The oil pressure pushes the springs (8) and the spool moves to the left.
Oil in passage (13) can now flow past the spool into port (14). The oil in port (14) flows to the head end of the right side steering cylinder and the rod end of the left side cylinder.
Oil from the rod end of the right side steering cylinder and the head end of the left side cylinder flows into port (12). The oil flows from port (12) back to the hydraulic tank.
The machine articulates left and the machine begins making a left turn. When the control lever is released, pilot oil flow to port (10) stops. Oil pressure on the retainer (9) must be removed before the spool can return to the neutral position. Because pilot oil flow is blocked, springs (8) cause the spool to return to the center position. As the spool travels to the right oil in springs (8) chamber will flow through port (10) and returns to the tank.
The spool blocks the flow of steering oil to the steering cylinders when the valve is in the neutral position. This causes the machine to be held in a turning position.
Blocked oil pressure at outlets (12) and (14) is sensed by the crossover relief valve in port (6). When the wheels contact a stationary object, the steering cylinders may experience a sudden shock load. Any pressure that is generated in the steering cylinders from the shock load is sensed in passages. The crossover relief valve (6) senses the oil pressure and opens. The relief valve will not allow pressure to rise above the
When the machine is turned to the right, the steering control valve operates in a similar manner.
For a right turn, pilot oil enters pilot port (4). Pressure oil from pump inlet port (2) flows through passage (13). The oil then flows past directional spool (5). From directional spool (5), the oil flows out of steering cylinder port (12).
The pressure oil then flows to the rod end of the steering cylinder on the right side of the machine. The oil also flows to the head end of the steering cylinder on the left side of the machine.
The oil then flows to the rod end of the right steering cylinder, and the head end of the left steering cylinder. This causes the machine to articulate to the right.