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| Illustration 1 | g00476324 |
Front View of Pilot Valve (Steering) (A) Steering shaft. (1) Pilot valve (steering). | |
The steering pilot valve is located on the non-engine end frame of the machine, and near the articulated hitch. Steering shaft (A) connects to steering pilot valve (1) .
General Description
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| Illustration 2 | g00437503 |
Bottom View of the Steering Pilot Valve (1) Steering pilot valve. (2) Port for neutralizer valve. (3) Port for neutralizer valve. (4) Port for the hydraulic oil tank. (5) Passage to hydraulic oil tank. (6) Pilot oil passage. (7) Pressure tap for pilot oil supply. (8) Port for pilot oil pressure. | |
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| Illustration 3 | g00437504 |
View A-A (1) Steering pilot valve. (9) Spring. (10) Drain passage. (11) Cam. (12) Control port for right turns. (13) Cavity for the directional control valve. (14) Shaft assembly. (15) Directional control valve. (16) Cavity. (17) Control port for left turns. (18) Plunger. (19) Housing. (20) Spring. (21) Valve spool. (22) Pressure regulating valve. (23) Passage (pilot pressure). (24) Body. (25) Supply port (pressure oil). (26) Adjusting screw. | |
Steering pilot valve (1) consists of directional control valve (15) and pressure regulating valve (22). Pressure regulating valve (22) controls the pressure from the pilot/brake pump for use by directional control valve (15). Pressure regulating valve (22) is actuated by cam (11) .
Both directional control valve (15) and cam (11) are mounted onto shaft assembly (14). Shaft assembly (14) connects to the steering wheel by a key and bolt assembly. When you rotate the steering wheel, directional control valve (15) and cam (11) rotate in the same direction as the steering wheel.
Pressure regulating valve (22) contains supply port (25) which connects to the pilot/brake pump. Passage (5) connects to the hydraulic oil tank. Passage (6) supplies regulated pilot pressure oil to directional control valve (15) .
Pressure regulating valve (22) also contains the following components. Spring (20), valve spool (21), body (24) and adjusting screw (26) .
Pilot oil flows into pressure regulating valve (22) through supply port (7). When you turn the steering wheel, cam (11) moves plunger (18) against spring (20) and valve spool (21). As valve spool (21) moves downward, valve spool (21) slides further into body (24) .
The pilot oil then flows between valve spool (21) and body (24). The flow of oil between these components functions as an orifice in passage (23). As valve spool (21) moves downward, the size of the orifice between valve spool (21) and body (24) becomes larger.
The larger orifice creates a smaller pressure drop. This increases the pressure of the pilot oil. The pressure level of the pilot oil in passage (6) is proportionate to the downward displacement of plunger (18) and valve spool (21) .
From passage (23), the regulated pilot pressure oil flows to directional control valve (15) through passage (6) .
Note: Pressure regulating valve (22) is adjustable. In order to increase the pilot pressure, turn adjustment screw (26) clockwise. In order to decrease the pilot pressure, turn adjustment screw (26) counterclockwise. In order to check the neutral pilot pressure oil, connect an appropriate oil pressure gauge to pressure port (8).
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| Illustration 4 | g00437505 |
View B-B (12) Control port for right turns. (15) Directional control valve. (17) Control port for left turns. (27) Passage. (28) Cavity. | |
The pilot oil flows from passage (6) through a passage in housing (19). The oil then flows to cavity (16) of directional control valve (15). From cavity (16), the pilot oil flows into cavity (28) through passage (27) .
Cavity (28) is located on the opposite side of directional control valve (15) from cavity (16). The equal pressure of the pilot oil in cavity (16) and in cavity (28) centers directional control valve (15) in cavity (13) .
Port (12) is for right turns. Port (12) connects to port (2). Port (17) is for left turns. Port (17) connects to port (3). Port (2) and port (3) connect to the steering neutralizer valves.
In the NEUTRAL position (no steering input), control ports (12) and (17) are blocked by directional control valve (15) .
As you rotate the steering wheel, directional control valve (15) also rotates. This allows pilot oil to flow into control port (12) or control port (17). When pilot oil flows into one of the control ports, the other control port opens to the hydraulic oil tank.
With no steering wheel input, spring (9), shaft assembly (14), cam (11) and directional control valve (15) return to the NEUTRAL position. When directional control valve (15) returns to the NEUTRAL position, both control ports are again blocked.
NEUTRAL Position
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| Illustration 5 | g00440985 |
Bottom View of the Steering Pilot Valve NEUTRAL Position (1) Steering pilot valve. (6) Pilot oil passage. (7) Pilot oil supply port. (8) Pressure tap for pilot oil. | |
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| Illustration 6 | g00441123 |
View A-A NEUTRAL Position (1) Steering pilot valve. (13) Cavity for directional control valve. (15) Directional control valve. (19) Housing. (21) Valve spool. (22) Pressure regulating valve. (23) Passage (pilot pressure). (24) Body. | |
In the NEUTRAL position, pilot oil enters pressure regulating valve (22) through supply port (7). The pilot pressure oil then flows between valve spool (21) and body (24). The flow of oil between these components functions as an orifice in passage (23) .
The pilot oil flows from passage (6) through a passage in housing (19). The oil then flows to a cavity in directional control valve (15) .
Two cavities are located opposite each other in directional control valve (15). The equal pressure of the pilot oil in these cavities causes directional control valve (15) to become centered in cavity (13).
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| Illustration 7 | g00437505 |
View B-B NEUTRAL Position (12) Control port for right turns. (15) Directional control valve. (17) Control port for left turns. (27) Passage. (28) Cavity. | |
In the NEUTRAL position (no steering input), control ports (12) and (17) are blocked by directional control valve (15) .
In order to check the regulated pilot pressure oil, connect an appropriate oil pressure gauge to pressure port (8). When the machine is in the NEUTRAL position, the pilot pressure at pressure tap (8) should equal 600 ± 15 kPa (87 ± 2 psi).
RIGHT TURN Position
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| Illustration 8 | g00441166 |
Bottom View of the Steering Pilot Valve RIGHT TURN Position (1) Steering pilot valve. (6) Pilot oil passage. | |
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| Illustration 9 | g00441167 |
View A-A RIGHT TURN Position (1) Steering pilot valve. (9) Spring. (11) Cam. (14) Shaft assembly. (15) Directional control valve. (18) Plunger. (20) Spring. (21) Valve spool. (24) Body. | |
When you turn the steering wheel clockwise in order to make a right turn, the rotary motion causes shaft assembly (14) to rotate. Shaft assembly (14) connects to both cam (11) and directional control valve (15) .
As you rotate the steering wheel, directional control valve (15) and cam (11) rotate in the same direction as the steering wheel. When you turn the steering wheel, cam (11) moves plunger (18) against spring (20) and valve spool (21). As valve spool (21) moves downward, valve spool (21) slides further into body (24) .
The pilot oil then flows between valve spool (21) and body (24). The flow of oil between these components functions as an orifice in passage (23). As valve spool (21) moves downward, the size of the orifice between valve spool (21) and body (24) becomes larger.
The larger orifice creates a smaller pressure drop. This increases the pressure of the pilot oil. The pressure level of the pilot oil in passage (6) is proportionate to the downward displacement of plunger (18) and valve spool (21) .
As you turn the steering wheel from the center NEUTRAL position, the size of the orifice increases. As the size of the orifice increases, the pilot pressure also increases. The higher pilot pressure level allows increased steering speed. When the steering wheel is fully turned, the pilot oil pressure should be a minimum of 1700 kPa (250 psi).
As you rotate the steering wheel, directional control valve (15) also rotates. This allows pilot oil to flow into control port (12). Control port (12) is for right turns. When pilot oil flows into control port (12), any oil in control port (17) drains back to the hydraulic oil tank. This causes the machine to turn right.
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| Illustration 10 | g00441168 |
View B-B RIGHT TURN Position (12) Control port for right turns. (15) Directional control valve. (17) Control port for left turns. (27) Passage. (28) Cavity. | |
When you release the steering wheel, spring (9) causes the following components to return to the NEUTRAL position. Shaft assembly (14), cam (11) and directional control valve (15) .
When directional control valve (15) returns to the NEUTRAL position, control port (12) is blocked.
LEFT TURN Position
When you turn the steering wheel counterclockwise in order to make a left turn, the steering pilot valve operates in a similar manner. However, when you make a left turn, pilot oil flows into control port (17). Any oil in control port (12) drains back to the hydraulic oil tank. This causes the machine to turn left.