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| Illustration 1 | g00374896 |
Steering Control Valve | |
The steering control valve is located on the right side of the machine under the operator's platform. The steering control valve is also located above the hydraulic oil tank.
NEUTRAL Position
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| Illustration 2 | g00362155 |
Schematic of the Steering Control Valve NEUTRAL Position (1) Steering control valve. (2) Steering crossover relief valve. (3) Port for the steering cylinder. (4) Port for the steering cylinder. (5) Shuttle valve. (6) Load sensing signal port. (7) Makeup check valve. (8) Pilot port "B". (9) Alternate pilot port "A". (10) Makeup check valve. (11) Pilot port "B". (12) Hydraulic oil tank port. (13) Directional spool. (14) Backup relief valve for the steering system. (15) Pressure reducing valve. (16) Reduced pilot pressure port. (17) Inlet from the steering pump. | |
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| Illustration 3 | g00638379 |
Steering Control Valve NEUTRAL Position (1) Steering control valve (2) Steering crossover relief valve (3) Port for the steering cylinder (4) Port for the steering cylinder (5) Shuttle valve (6) Load sensing signal port (7) Makeup check valve (8) Pilot port "A" (9) Alternate pilot port "B" (10) Makeup check valve (11) Pilot port "A" (12) Hydraulic oil tank port (13) Directional spool (14) Backup relief valve for the steering system (15) Pressure reducing valve (16) Reduced pilot pressure port (17) Inlet from the steering pump | |
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| Illustration 4 | g00638385 |
View C-C NEUTRAL Position (9) Pilot port "A". (11) Pilot port "B". (13) Directional spool. (18) Spring. (19) Drain passage to the hydraulic oil tank. (20) Passage to steering cylinder. (21) Passage for the inlet from the steering pump. (22) Passage to steering cylinder. (23) Drain passage to the hydraulic oil tank. (24) Passage to steering cylinder port (3). (25) Passage to steering cylinder port (4) . | |
With the engine in operation, oil is drawn from the hydraulic oil tank to the steering pump. The pressure oil then flows to steering control valve (1) .
Note: Machines that are equipped with the secondary steering attachment have several additional components. The components include the secondary steering pump and electric motor, and a secondary steering valve. If your machine includes the secondary steering attachment, the pressure oil from the steering pump flows to the secondary steering valve before the oil flows to the steering control valve.
Pressure oil from the steering pump enters steering control valve (1) through inlet (17). From inlet (17), the pressure oil flows to steering backup relief valve (14) and pressure reducing valve (15) .
The pressure oil then flows to directional spool (13). When the steering wheel is in the NEUTRAL position, steering control valve (1) is in the NEUTRAL position.
The flow of pilot oil to either end of directional spool (13) is blocked when the steering wheel is in the NEUTRAL position. This causes spring (18) to keep directional spool (13) in the NEUTRAL position.
This causes directional spool (13) to block the flow of pressure oil from the steering pump. Because no pressure oil is allowed to flow through passages (20) or (22), the steering cylinders do not actuate. When the steering wheel is in the NEUTRAL position, directional spool (13) is in the NEUTRAL position.
Similarly, if the steering neutralizer valve for a left turn or the steering neutralizer valve for a right turn is actuated, the flow of steering pilot oil to either end of directional spool (13) stops.
Load sensing signal port (6) connects to the control section of the steering pump. The control section consists of a pressure and flow compensator valve. The pressure and flow compensator valve regulates the output of the steering pump.
The pressure and flow compensator valve is attached to the steering pump. The compensator valve adjusts the outlet flow of the pump so that the pressure at the pump outlet is approximately 2400 kPa (350 psi) higher than the pressure in the steering cylinders.
As an example, if the steering cylinder pressure that is required to turn the machine is 10000 kPa (1450 psi), the pressure at the pump will be 12400 kPa (1800 psi). The pressure increases in the steering cylinder until the machine begins to turn.
When the steering wheel is held stationary in the NEUTRAL position, there is no demand for pressure oil. The low signal pressure causes the steering pump to destroke. This causes the pump outlet pressure to be slightly higher than the pressure at the compensator valve.
The pressure in the steering cylinders is sensed by shuttle valve (5). This same oil pressure is in the signal pressure line that connects to the pressure and flow compensator valve. If the pressure in the steering cylinders is equal to the pressure in the hydraulic oil tank, then the steering pump will destroke. The steering pump will destroke to low pressure standby. This small amount of oil flow compensates for system leakage.
Pressure reducing valve (15) lowers the pressure of the steering pump to pilot oil pressure. However, this valve only functions as a secondary source of pilot oil. The primary source of pilot oil flows from the pilot/brake pump to a pressure reducing valve in the implement circuit. The pilot oil then flows to a shuttle valve in the steering circuit.
If the pilot/brake pump can not provide an adequate amount of pilot oil for the steering circuit, pressure reducing valve (15) is able to supply the pilot oil.
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 (20) or (22). Crossover relief valve (2) senses oil pressure in passages (20) and (22) .
If the pressure exceeds the setting of crossover relief valve (5), the crossover relief valve opens. This causes the oil to flow to the passage with the lower pressure.
Makeup check valves (7) and (10) connect with passages (20) and (22). Makeup check valves (7) and (10) allow oil to be drawn through hydraulic oil tank port (12). This prevents voiding in the steering cylinder. Makeup check valves (7) and (10) are normally seated by spring force.
LEFT TURN Position
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| Illustration 5 | g00379854 |
Schematic of the Steering Control Valve LEFT TURN Position (1) Steering control valve. (2) Steering crossover relief valve. (3) Port for the steering cylinder. (4) Port for the steering cylinder. (5) Shuttle valve. (6) Load sensing signal port. (7) Makeup check valve. (8) Pilot port "A". (9) Alternate pilot port "A". (10) Makeup check valve. (11) Pilot port "B". (12) Hydraulic oil tank port. (13) Directional spool. (14) Backup relief valve for the steering system. (15) Pressure reducing valve. (16) Reduced pilot pressure port. (17) Inlet from the steering pump. | |
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| Illustration 6 | g00638399 |
View C-C LEFT TURN Position (9) Pilot port "A". (13) Directional spool. (18) Spring. (19) Drain passage to the hydraulic oil tank. (20) Passage to steering cylinder. (21) Passage for the inlet from the steering pump. (22) Passage to steering cylinder. (23) Drain passage to the hydraulic oil tank. (24) Chamber. (25) Retainer. (26) Bolt. (27) Passage to steering cylinder port (3). (28) Passage to steering cylinder port (4). (29) Cavity. | |
When you turn the steering wheel counterclockwise in order to make a left turn, the steering shaft rotates the shaft for the steering pilot valve. The rotation actuates the steering pilot valve. When the steering pilot valve is in the OPEN position, pilot oil is allowed to flow.
The pilot oil flows from the steering pilot valve and through the steering quad check valve. The pilot oil then flows through the neutralizer valve for left turns, and into steering control valve (1) through pilot port (9) .
The pilot oil fills chamber (24). The pressure of the pilot oil in chamber (24) causes directional spool (13) to move right. Bolt (26) is fastened to the end of directional spool (13). Because bolt (26) secures retainer (25), the movement causes spring (18) to compress to the right.
The movement of directional spool (13) causes metering orifices in the spool to open into a passage.
Oil that is displaced from cavity (29) by the movement of directional spool (13) flows back to the hydraulic oil tank.
As directional spool (13) moves to the right, pressure oil from the steering pump flows through inlet (17). The oil then flows through pump inlet passage (21) and flows through slots in spool (13). The oil then flows into passage (27). Passage (27) connects to steering cylinder port (4) .
The pressure oil then flows out of steering cylinder port (4). The pressure oil then flows to the head end of the steering cylinder on the right side of the machine. The pressure oil also flows to the rod end of the steering cylinder on the left side of the machine.
At the same time, return oil from the rod end of the steering cylinder on the right side of the machine flows through port (3). Return oil from the head end of the steering cylinder on the left side of the machine also flows through port (3). This causes the machine to articulate to the left.
The return oil then flows into passage (28). From passage (28), the oil flows through a passage to port (12). Port (12) connects to the hydraulic oil tank.
As the machine begins to turn, the shaft for the steering pilot valve begins to rotate to the CLOSED position. As the shaft of the pilot valve rotates closer to the CLOSED position, the turning speed of the machine is reduced.
However, the machine continues to turn to the left until the steering wheel returns to the NEUTRAL position. When the steering wheel returns to the NEUTRAL position, the steering pilot control valve blocks the flow of pilot oil to the steering control valve.
This causes the pressure in cavity (24) to decrease. This also allows spring (18) to move directional spool (13) to the NEUTRAL position. When directional spool (13) reaches the NEUTRAL position, the machine stops turning.
When a wheel hits 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 (20) or (22). Oil pressure in passages (20) and (22) is sensed by crossover relief valve (2) .
If the pressure exceeds the setting of steering crossover relief valve (2), the crossover relief valve opens. This causes the oil to flow to the passage with the lower pressure.
Makeup check valves (7) and (10) connect with passages (20) and (22). Makeup check valves (7) and (10) allow oil to be drawn from the hydraulic oil tank. This prevents voiding in the steering cylinder. Makeup check valves (7) and (10) are normally seated by spring force.
Note: The machine turns at a speed that depends on the rotational position of the steering wheel. The turning speed of the machine does not depend on the turning speed of the steering wheel.
If a constant turning speed is desired, you must adjust the rotational position of the steering wheel. Continuing to adjust the rotational position of the steering wheel will keep the steering pilot valve open as the machine turns.
In order to increase the turning speed of the machine, you must adjust the rotational position of the steering wheel. You must also adjust the rotational position of the steering wheel in order to decrease the turning speed of the machine.
RIGHT TURN Position
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| Illustration 7 | g00362162 |
Schematic of the Steering Control Valve RIGHT TURN Position (1) Steering control valve. (2) Steering crossover relief valve. (3) Port for the steering cylinder. (4) Port for the steering cylinder. (5) Shuttle valve. (6) Load sensing signal port. (7) Makeup check valve. (8) Pilot port "B". (9) Alternate pilot port "A". (10) Makeup check valve. (11) Pilot port "B". (12) Hydraulic oil tank port. (13) Directional spool. (14) Backup relief valve for the steering system. (15) Pressure reducing valve. (16) Reduced pilot pressure port. (17) Inlet from the steering pump. | |
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| Illustration 8 | g00379873 |
View C-C RIGHT TURN Position (11) Pilot port "B". (13) Directional spool. (18) Spring. (19) Drain passage to the hydraulic oil tank. (20) Passage to steering cylinder. (21) Passage for the inlet from the steering pump. (22) Passage to steering cylinder. (23) Drain passage to the hydraulic oil tank. (24) Washer. (25) Chamber. (26) Port for the steering cylinder. (27) Port for the steering cylinder. (28) Cavity. | |
When the machine is turned to the right, the steering control valve operates in a similar manner.
When you turn the steering wheel clockwise in order to make a right turn, pilot oil enters pilot port (11). The oil fills cavity (28). The pressure of the oil in cavity (28) causes directional spool (13) to move left. As spool (13) moves to the left, washer (24) will also move to the left. This causes spring (18) to compress. Any oil that was in chamber (25) flows back to the hydraulic oil tank.
When directional spool (13) moves left, pressure oil flows from pump inlet passage (21) and flows through slots in spool (13). The oil then flows into steering cylinder passage (22) and out of steering cylinder port (27) .
The pressure oil then flows out of the port for steering cylinder for right turns (3). The pressure oil then flows to the head end of the steering cylinder on the left side of the machine. The pressure oil also flows to the rod end of the steering cylinder on the right side of the machine.
At the same time, the return oil flows from the head end of the steering cylinder on the right side of the machine. The return oil also flows from the rod end of the steering cylinder on the left side of the machine. This causes the machine to articulate to the right. The return oil flows back to the hydraulic oil tank.
Crossover Relief Valve for the Steering Cylinders
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| Illustration 9 | g00375194 |
Crossover Relief Valve for the Steering Cylinders | |
The crossover relief valve for the steering cylinders is located on the front right side of the steering control valve as you face the right side of the machine.
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| Illustration 10 | g00375313 |
Schematic for the Steering Control Valve Crossover Relief Valve for the Steering Cylinders | |
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| Illustration 11 | g00279630 |
Crossover Relief Valve for the Steering Cylinders (1) Screw. (2) Jam nut. (3) Spring. (4) Spring chamber. (5) Sleeve. (6) Holes. (7) Valve face. (8) Passage. (9) Poppet for the relief valve. (10) Drain hole. (11) Face of sleeve. (12) Passage. (13) Valve face. (14) Valve seat. | |
The crossover relief valve for the steering cylinders relieves shock loading in the steering system. The crossover relief valve operates when the steering system is in neutral or when the steering system is articulating the machine.
Steering cylinder pressure is sensed in passages (8) and (12) of the steering control valve. Steering cylinder pressure is also sensed on valve faces (7) and (13) .
When the steering cylinders are moved by external steering forces, the pressure in passages (8) and (12) can increase suddenly.
A pressure increase in passage (8) acts on valve face (7). If the pressure is greater than the valve setting, poppet (9) moves left. This causes spring (3) to compress. The pressure is relieved to passage (12) through holes (6) .
If the pressure in passage (12) is greater than the pressure setting of the crossover relief valve, the pressure acts on valve face (13). The pressure also acts on the face of sleeve (11) .
Sleeve (5) and poppet (9) move to the left against spring (3). The pressure in passage (12) is relieved to passage (8) through holes (6) .
Spring chamber (4) is connected to the hydraulic oil tank through drain hole (10) .
The pressure setting of the crossover relief valve for the steering cylinders is adjustable.
As an example, a left turn is made and the valve spool is returned to the NEUTRAL position. A force which causes the machine to turn to the right is placed on the machine. Because the oil is trapped in the cylinder lines, this force causes the pressure in the cylinder lines to increase.
When the pressure exceeds the setting of the crossover relief valve, the relief valve opens. This causes oil to flow from the rod end of the left steering cylinder. The oil then flows to the rod end of the right steering cylinder.
Similarly, oil that is trapped in the head end of the right steering cylinder flows to the head end of the left steering cylinder. This causes the machine to articulate to the right. This also reduces the pressure in the lines for the steering cylinders.
Reference: For additional information on the adjustment procedure for the crossover relief valve, refer to the Service Manual module for Testing And Adjusting, SENR1384, "950G Wheel Loader and 962G Wheel Loader Steering System", "Steering Cylinder Crossover Relief Valve - Test and Adjust".
Backup Relief Valve for the Steering System
Note: In the following illustration, the operator's cab is removed for clarity.
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| Illustration 12 | g00375316 |
Backup Relief Valve for the Steering System | |
The backup relief valve for the steering system is located on the left rear side of the steering control valve as you face the right side of the machine.
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| Illustration 13 | g00375399 |
Schematic for the Steering Control Valve Backup Relief Valve for the Steering System | |
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| Illustration 14 | g00279628 |
Backup Relief Valve for the Steering System (1) Screw. (2) Jam nut. (3) Spring chamber. (4) Spring. (5) Outlet hole to the hydraulic oil tank. (6) Outlet hole. (7) Inlet hole from the steering pump. (8) Valve seat. (9) Poppet for the relief valve. (10) Drain hole. (11) Drain hole. (12) Annular face. | |
Pressure may suddenly increase due to steering resistance. If the high pressure cutoff spool in the steering pump's compensator valve does not regulate the maximum output pressure of the steering pump, the backup relief valve will regulate the pump output pressure by directing the pump flow back to the hydraulic oil tank.
Spring (4) holds steering relief valve poppet (9) against valve seat (8) .
Steering pump pressure is sensed in the backup relief valve through holes (7). This pressure acts on annular face (12) .
If the pressure that is acting on annular face (12) exceeds the pressure setting on the backup relief valve, poppet (9) moves to the left against spring (4) .
Pressure is then relieved to the hydraulic oil tank through outlet holes (5) and (6) .
Drain holes (10) and (11) connect spring chamber (3) to the hydraulic oil tank.
The pressure setting of the backup relief valve for the steering system is adjustable.
Reference: For additional information on the adjustment procedure for the backup relief valve, refer to the Service Manual module for Testing And Adjusting, SENR1384, "950G Wheel Loader and 962G Wheel Loader Steering System", "Steering Control Valve Pump Pressure Backup Relief Valve - Test and Adjust".