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| Illustration 1 | g03866155 |
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(1) Left cylinder
(2) Right cylinder (3) Crossover relief (4) Load sense resolver (5) Left cylinder make-up valve (6) Right cylinder make-up valve (7) Load sense relief (8) Primary pressure reducing valve (9) Primary pilot control pressure (10) Secondary steering diverter (11) Secondary steering pump check (12) Secondary Pump (13) Secondary pump relief (14) Margin relief (15) Tank (16) Load sense (17) Primary pump (18) Primary pump check (19) Pilot supply B (20) Backup pilot control pressure (21) Backup pressure reducing valve (22) Pilot supply A (23) Spool | |
The steering control valve is mounted on a plate on the right frame beneath the machine platform.
When the STIC steering control lever is in the CENTER position, the flow of pilot oil to either end of spool (23) stops. Similarly, if a neutralizer valve for a left or right turn is actuated, the flow of pilot oil to either end of spool (23) stops.
When no pilot oil is acting on either end of spool (23), centering springs return spool (23) to the NEUTRAL position. As the spool returns to NEUTRAL position, pilot oil acting on the end of spool (23) is forced across an orifice and back to tank.
When spool (23) is in the CENTER position, oil in the ports to the cylinders are blocked. This causes oil in the steering cylinder lines to be blocked.
The load sense resolver (4) senses the load on the cylinder. The resolver then directs the signal oil to flow back to the primary steering pump. This action causes the pump to destroke. When this situation occurs, there is only enough oil in order to compensate for leaks.
Note: If the machine is moving and turned at the same time, the machine will continue to move in the direction of the last selected travel position of the STIC. When you release the STIC steering control lever, the machine will not return to the STRAIGHT AHEAD travel position.
If the pilot oil pump fails, pressure oil from the steering pump flows through the pressure reducing valve in the steering control valve. The oil then flows through a pilot check valve and onto the pilot valve. Pressure reducing valve (1) reduces pump pressure to pilot pressure.
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| Illustration 2 | g03866227 |
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(1) Left cylinder
(2) Right cylinder (3) Crossover relief (4) Load sense resolver (5) Left cylinder make-up valve (6) Right cylinder make-up valve (7) Load sense relief (8) Primary pressure reducing valve (9) Primary pilot control pressure (10) Secondary steering diverter (11) Secondary steering pump check (12) Secondary Pump (13) Secondary pump relief (14) Margin relief (15) Tank (16) Load sense (17) Primary pump (18) Primary pump check (19) Pilot supply B (20) Backup pilot control pressure (21) Backup pressure reducing valve (22) Pilot supply A (23) Spool | |
When the operator moves the STIC to make a left turn, pilot oil flows from the pilot valve through the left neutralizer valve. The oil then flows through the neutralizer check valves and to pilot oil port (22). The pilot oil acts against spool (23). The force of the oil overcomes the springs. This causes spool (23) to move to the right.
When spool (23) moves to the right, oil in the passage flows past spool (23). The oil then flows through the lines to the rod end of the left steering cylinder. The oil in the port also flows through the lines to the head end of the right steering cylinder.
Oil from the rod end of the right steering cylinder (2) flows into the return port. The oil from the head end of the left steering cylinder flows into the return port. The oil then flows to the hydraulic tank.
This action causes the machine to articulate to the left. When the STIC steering control lever is released, the flow of pilot oil stops. Oil that is acting against spool (23) must be removed before spool (23) can return to the NEUTRAL position.
Because the pilot oil is blocked and draining to tank through the orifice, the springs cause spool (23) to move back to the CENTER position.
When the STIC steering control lever is in the NEUTRAL position, valve spool (23) blocks the flow of oil to both steering cylinders. This action keeps the machine in the LEFT TURN position.
The pressure of the oil in the ports is sensed in the port for steering cylinder crossover relief valve (3).
If an outside force tries to turn the machine, and if valve spool (23) is in the NEUTRAL position, an increase in pressure will occur. The increase in pressure will open steering cylinder crossover relief valve (3).
Secondary steering relief valve (13) limits secondary steering oil pressure during operation with the secondary steering pump.
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| Illustration 3 | g03866330 |
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(1) Left cylinder
(2) Right cylinder (3) Crossover relief (4) Load sense resolver (5) Left cylinder make-up valve (6) Right cylinder make-up valve (7) Load sense relief (8) Primary pressure reducing valve (9) Primary pilot control pressure (10) Secondary steering diverter (11) Secondary steering pump check (12) Secondary Pump (13) Secondary pump relief (14) Margin relief (15) Tank (16) Load sense (17) Primary pump (18) Primary pump check (19) Pilot supply B (20) Backup pilot control pressure (21) Backup pressure reducing valve (22) Pilot supply A (23) Spool | |
When the steering control valve is in the RIGHT TURN position, the valve operates in a similar manner as the LEFT TURN position.
For a right turn, pilot oil enters pilot oil port (19). This moves spool (23) to the left. Pressure oil from the inlet flows through . The oil then flows past spool (23) and into the port for right turns.
The oil then flows through the lines to the head end of the left steering cylinder. The oil in the port also flows through the lines to the rod end of the right steering cylinder. This action causes the machine to articulate to the right.
Secondary Steering (NEUTRAL Position)
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| Illustration 4 | g03867818 |
The basic components of a standard steering control and secondary steering are the same. However, secondary steering control contains the following additional components:
- Primary pressure reducing valve
- Primary pilot control pressure
- Secondary steering diverter
- Secondary steering pump check
- Secondary Pump
- Secondary pump relief
If the primary steering pump fails, diverter valve (10) sends oil from the secondary steering pump to the control valve. The oil is pumped past check valve (11) into the oil passage. This action will continue to occur when the machine is moving forward or backward.
When the engine is running, oil flows from the hydraulic tank to the primary steering pump.