The pilot valve (joystick) controls the flow of pilot oil to the main control valve. Then, the main control valve controls the flow of pump supply oil to the implement cylinders.
Note: The pilot valve in illustration 1 is for machines with an auxiliary function (logging fork, side dump bucket, multipurpose bucket, etc). Machines without an auxiliary function will not have auxiliary valve (2).
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| Illustration 1 | g00899972 |
View of the Pilot Valve (Joystick) (1) Lift function and tilt function. (2) Auxiliary function. | |
In the pilot hydraulic system, oil pressure is provided by the pilot/brake pump. The oil is directed to both the brake system and the pilot system. The oil that is directed to the pilot system will flow through the inlet filter screen. Then, the pilot oil flows into the primary reducing valve. The primary reducing valve is adjusted higher than the secondary reducing valve. The pilot oil will shift the spool in the shuttle valve and the pilot oil will flow through an open ball valve to the pilot valve (joystick).
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| Illustration 2 | g00900010 |
Location of the Hydraulic Connectors (3) Tilt back. (4) Tank port. (5) Raise. (6) Pilot pressure inlet. (7) Dump. (8) Auxiliary 2. (9) Auxiliary 1. (10) Auxiliary valve. (11) Lower | |
Note: The pilot valve in Illustration 2 is for machines with an auxiliary function. Machines without an auxiliary function will not have auxiliary valve (10) .
The pilot oil enters the implement joystick at the pilot pressure inlet (6). Illustration 2 shows the position of the pilot pressure inlet, the connector for the return line, and the connectors of the lines which go to the end caps of the main relief valve.
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| Illustration 3 | g00900067 |
Sectional View of the Joystick Control Tilt Valve in the Hold Position (12) Plunger (13) Lever assembly (14) Adjustment pin (15) Retainer (16) Cup (17) Upper plunger (18) Centering spring (19) Ball (20) Detent coil (21) Retainer (22) Passage to tank port (23) Spool (24) Spring (pressure control) (25) Passage to the return port (26) Passage to the control port (27) Orifice (28) Bias spring (29) Pilot oil supply passage (30) Control port to main control valve (31) Pilot oil supply port | |
When the hand lever is moved, lever assembly (13) will be activated. Adjustment pin (14) will push down on the upper plunger (17).
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| Illustration 4 | g00900573 |
Sectional View of an Engaged Coil Assembly (12) Plunger. (13) Lever assembly. (14) Adjustment pin. (15) Retainer. (16) Cup. (20) Detent coil. | |
The joystick control is equipped with detent coils. When the joystick control is activated to 90 percent of lever travel, retainer (15) contacts coil assembly (20). If detent coil (20) is energized, the coil assembly will hold retainer (15). The joystick will be held in position until the kickout switch interrupts the flow of current to the coil. When the detent coil de-energizes, lever assembly (13) returns to the HOLD position. Plunger assembly (12) initiates a force against cup (16) in order to assist the spring in pulling retainer (15) from detent coil (20) .
The flow of pilot oil through the system is controlled by the cartridge assembly. The movement of each spool in the main control valve is determined by the individual cartridge assembly. The location of the cartridge assembly is shown in Illustration 3. The following sections explain the operation of the cartridge assembly.
The Cartridge in the HOLD Position
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| Illustration 5 | g00900497 |
Sectional View of the Cartridge Assembly (18) Centering spring. (23) Spool. (24) Spring (pressure control). (25) Passage to the return port. (26) Passage to the control port. (28) Bias spring. (29) Passage to the supply port. (32) Hole. (33) Chamber. | |
When the cartridge assembly is in the HOLD position, centering spring (18,), the spring (pressure control) (24), and bias spring (28) keep lever assembly (13) in the HOLD position.
Pilot pressure oil flows into the joystick control through the port at the bottom of the valve. Pilot oil flows through passage (31). This is shown in the Illustration 3. The passage takes the oil to port (26) of the cartridge assembly. The pilot oil will flow around spool (23). The pilot oil will flow through port (25) to tank port (22) .
The position of spool (24) blocks pilot oil supply passage (29). The pilot oil is prevented from flowing into control chamber (26). The controlled pressure chambers are open to return port (25). This also provides a passage for the pilot lines from the main control valve to return port (23). Return port (23) provides a path back to the hydraulic oil tank. Illustration 5 shows the flow of pilot oil through the cartridge assembly in the HOLD position.
Bias spring (28) is always active, but the force is slight. In the HOLD position, oil flows through hole (32) and through the center of spool (23). The oil flows into chamber (33). The oil is held in the chamber until the spool is moved.
The Cartridge with an Activated Spool
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| Illustration 6 | g00900316 |
Sectional View of the Cartridge Assembly (17) Upper plunger. (18) Centering spring. (21) Retainer. (23) Spool. (24) spring (pressure control). (25) Passage to the return port. (26) Passage to the control port. (27) Orifice. (28) Bias spring. (29) Passage to the supply port. (32) Hole. (33) Chamber. | |
In order to move an implement, the flow of oil in the main control valve must be routed to a cylinder. This is accomplished by sending pilot oil from the joystick to the end cap of the main control valve. When the joystick is moved, lever assembly (13) causes upper plunger (17) to move downward. As upper plunger (11) moves downward, the force on retainer (21) overcomes the spring (pressure control) (24) .
As the spring (pressure control) (24) compresses, spool (23) moves against bias spring (28). This moves spool (23) which closes the passage to the hydraulic oil tank. At the same time, pilot oil supply passage (29) opens. The pilot oil flows from pilot oil supply passage (29) around spool (23) and into passage (26). The oil pressure at passage (26) to the control port also increases.
As upper plunger (17) continues to move down, pressure at passage (26) to the control port increases. The spool in the main control valve starts to move. High pressure oil is sent to the end of the appropriate cylinder.
At the same time as spool (23) is moving in the downward direction, pressure of the oil in chamber (33) increases. The trapped oil is forced through orifice (27). This helps to dampen the valve. The combination of the oil in chamber (33) and bias spring (28) increases the stability of the valve.
Cartridge in Ball Lock
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| Illustration 7 | g00900512 |
Sectional View of the Cartridge Assembly (17) Upper plunger. (18) Centering spring. (19) Ball. (21) Retainer. (23) Spool. (24) Spring (pressure control). (26) Passage to the control port. (28) Bias spring. (29) Passage to the supply port. | |
At approximately 85 percent of lever travel, ball (19) contacts both upper plunger (17) and spool (23). The opposing force of the spring (pressure control) (24) will no longer have an effect on the pilot pressure. The spring is removed from the equation. This will equalize the oil pressure between passage (26) and pilot supply passage (31).