Neutral Position
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| Illustration 1 | g00278246 |
Neutral Position (1) Left steering cylinder port. (2) Steering crossover relief valve. (3) Right steering cylinder port. (4) Spool valve. (5) Tank return port. (6) Tank port. (7) Steering backup relief valve. (8) Pump inlet. (9) Pilot port for the left steering cylinder. (10) Pilot port for the right steering cylinder. (11) Selector valve. (12) Steering metering pump supply port. | |
Note: The illustration does not represent a cross section of the valve. Components that are shown in the illustration below are out of position for clarity.
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| Illustration 2 | g00283542 |
(13) Pilot spool. (14) Passage. (15) Passage. (16) Makeup valve. (17) Pilot chamber. (18) Metering orifices. (19) Pilot load check valve. (20) Passage. (21) Passage. (22) Passage. (23) Passage. (24) Makeup valve. (25) Centering springs. (26) Pilot chamber. (27) Metering orifices. (28) Directional spool. (29) Restrictor (metering pump supply). (A) Blocked oil. (B) Pump oil. | |
Directional spool (28) is held in the center position by centering springs (25) which blocks pump oil from inlet port (8) .
Pump standby pressure is sensed by steering backup relief valve (7). Pump standby pressure is connected to the steering metering pump through restrictor (29) in metering pump supply port (12). A small quantity of oil bleeds to the hydraulic tank through a restrictor that is installed in the steering metering pump.
The steering cylinders are connected to the steering control valve through ports (1) and (3) which are connected to passages (15) and (23) .
When the steering wheel stops moving, the steering cylinders are held in position by oil blocked in passages (15) and (23) .
Oil pressure in passages (15) and (23) is sensed by steering crossover relief valve (2). Makeup valves (16) and (24) are connected to passages (15) and (23). Makeup valves (16) and (24) are normally seated by spring force.
When the steering cylinders are moved by shock loading on the wheels, the pressure that is generated in the steering cylinders is sensed in passage (15) or (23) .
If the pressure exceeds the setting of the steering crossover relief valve, the steering crossover relief valve will open and oil flow will be unloaded to the lower pressure passage.
Makeup valves (16) and (24) prevent voiding in the steering cylinder which is opening. This allows oil to be drawn from hydraulic oil tank port (6) .
Left Turn Position
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| Illustration 3 | g00278246 |
Left Turn Position (1) Left steering cylinder port. (2) Steering crossover relief valve. (3) Right steering cylinder port. (4) Spool valve. (5) Tank return port. (6) Tank port. (7) Steering backup relief valve. (8) Pump inlet. (9) Pilot port for the left steering cylinder. (10) Pilot port for the right steering cylinder. (11) Selector valve. (12) Steering metering pump supply port. | |
Note: The illustration does not represent a cross section of the valve. Components that are shown in the illustration below are out of position for clarity.
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| Illustration 4 | g00278446 |
(13) Pilot spool. (14) Passage. (15) Passage. (16) Makeup valve. (17) Pilot chamber. (18) Metering orifices. (19) Pilot load check valve. (20) Passage. (21) Passage. (22) Passage. (23) Passage. (24) Makeup valve. (25) Centering springs. (26) Pilot chamber. (27) Metering orifices. (28) Directional spool. (29) Restrictor (metering pump supply). (A) Blocked oil. (B) Pump oil. (C) Return oil. | |
When the steering wheel is turned counterclockwise to make a left turn, pilot oil from the steering metering pump enters the valve through pilot port (9) .
Pilot spool (13) is moved to the left and oil flows through passage (14) to chamber (17) .
Directional spool (28) is moved to the left against the force of spring (25) and metering orifices (18) are aligned with passage (20). This allows the pilot pressure to open pilot load check valve (19) .
Oil that is displaced from chamber (26) by the movement of the directional spool passes through passages (20) and (21) to chamber (17) .
As the directional spool moves to the left, pump inlet (8) is connected to left steering cylinder port (1). This causes pump oil to pass into the head end of the right steering cylinder. This also causes pump oil to pass into the rod end of the left steering cylinder.
Oil from the rod end of the right cylinder flows into the steering control valve through right steering cylinder port (3) and to the hydraulic oil tank through port (17). Oil from the head end of the left cylinder flows into the valve through cylinder port (3) and to the hydraulic tank through port (17) .
Steering cylinder pressure is now passed through the open load check valve (19) to chamber (17). Steering cylinder pressure is also passed through passages (9) and (14) to the load sensing port of the steering metering pump.
The load sensing port for the steering metering pump is connected to the control section of the primary pump, which adjusts output to the required level.
The distance the directional spool is moved and the speed the machine turns depends on the speed the steering wheel is turned and the speed of the engine.
Restrictor (29) regulates the oil supply to the steering metering pump. Restrictor (29) regulates the maximum turning speed of the steering wheel.
As the maximum speed is reached, pilot oil pressure between the steering metering pump and the directional spool will decrease. The pump output will decrease slightly as the signal pressure of the sensing line decreases. This results in a heavier feel at the steering wheel which slows steering wheel rotation.
When steering wheel rotation is stopped, the steering metering pump is spring centered and the pilot oil flow to the steering control valve is cut off.
Steering cylinder pressure closes pilot load check valve (19) and centering spring (25) moves the directional spool to the center position.
Pilot oil in chamber (17) is displaced through orifices (18) and pilot passages (20) and (21) to chamber (26) .
Right Turn Position
The operation of steering to the right is similar to the description for steering to the left.
Steering Crossover Relief Valve
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| Illustration 5 | g00279630 |
Steering Crossover Relief Valve (1) Screw. (2) Jam nut. (3) Spring. (4) Spring chamber. (5) Sleeve. (6) Holes. (7) Valve face. (8) Passage. (9) Steering relief valve poppet. (10) Drain hole. (11) Face of sleeve. (12) Passage. (13) Valve face. (14) Valve seat. | |
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| Illustration 6 | g00278461 |
Schematic for the Steering Control Valve (15) Steering crossover relief valve. | |
The steering crossover relief valve is installed in the steering control valve.
The steering crossover relief valve relieves shock loading in the steering system. The steering crossover relief valve operates when the system is in neutral or when the system is articulating the machine.
Steering cylinder pressures are sensed in passages (8) and (12) of the steering control valve and on faces (7) and (13) of steering relief valve poppet (9) .
The pressure in either of the passages can rise suddenly when the steering cylinders are moved by external steering forces that are applied to the wheels.
A pressure increase in passage (8) acts on valve face (7) of the steering relief valve poppet. If the pressure is above the valve setting, the poppet will move left against the force of spring (3). The pressure is relieved to passage (12) through holes (6) .
A pressure increase in passage (12) above the valve setting acts on valve face (13) of the poppet and on face (11) of sleeve (5) .
The sleeve and the poppet shift to the left against the spring. The pressure in passage (12) is relieved to passage (8) through holes (6) .
Spring chamber (4) is connected to the tank through drain hole (10) .
The pressure setting of the steering crossover relief valve can be adjusted by screw (1) and by jam nut (2) .
Steering Backup Relief Valve
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| Illustration 7 | g00279628 |
Steering Backup Relief Valve (1) Screw. (2) Jam nut. (3) Spring chamber. (4) Spring. (5) Outlet hole of tank. (6) Outlet hole. (7) Inlet hole of pump. (8) Valve seat. (9) Steering relief valve poppet. (10) Drain hole. (11) Drain hole. (12) Annular face. | |
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| Illustration 8 | g00278462 |
Schematic for the Steering Control Valve (13) Steering backup relief valve. | |
Steering backup relief valve (13) is installed in the steering control valve.
Pressure may suddenly rise due to steering resistance. The load control of the pump may not regulate the pump output at a fast enough rate. If this occurs, the valve connects the inlet passage of the steering control valve to the hydraulic tank.
Spring (4) holds relief valve poppet (9) against seat (8) .
Pump pressure is sensed in the steering 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 valve pressure setting, the poppet is shifted to the left against the resistance of spring (4) .
Pressure is then relieved to the hydraulic oil tank through holes (5) and (6) .
Holes (10) and (11) connect the spring chamber to the hydraulic tank.
The pressure setting of the steering backup relief valve can be adjusted by screw (1) or by jam nut (2) .