Schematic for the Boom Hydraulic System
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| Illustration 1 | g00889918 |
(1) Boom I control valve (2) Boom cylinder (3) Main control valve (4) Pump (5) Boom II control valve (6) Pilot control valve (7) Pilot control valve (8) Pilot and travel speed manifold (A) Oil that is supplied to the main control valve (B) Pilot oil for shifting the boom spool to the BOOM LOWER position (C) Pilot oil for shifting the boom spool to the BOOM RAISE position (D) Oil that is supplied to the pump by the hydraulic tank (E) Oil that is supplied to the pilot and travel speed manifold by the pilot pump | |
Note: The joystick controls for the boom hydraulic system can be set to a Standard pattern or an Alternate pattern (if equipped). The hydraulic activation control must be activated in order for the pilot valves (joysticks) to function.
In the Standard pattern, the boom hydraulic system is controlled by the right pilot valve (joystick). When the right pilot valve (joystick) is moved forward, the boom will lower. When the right pilot valve (joystick) is moved backward, the boom will raise. When the pilot valve (joystick) is released from either position, the pilot valve (joystick) will return to the HOLD position.
Reference: Refer to the Operation and Maintenance Manual, "Joystick Controls" for more information on the operation of the pilot valve (joysticks).
Boom Lower
When the pilot valve (joystick) is moved forward, pilot oil (B) shifts the spool of boom I control valve (1) upward. Supply oil (A) is routed from the pump (4) to the main control valve (3). The pump receives oil from the hydraulic tank through the hydraulic line (D). The supply oil flows to the rod end of the boom cylinder (2) through the boom I control valve. This causes the cylinder rod to retract. The retracting of the cylinder rod causes the boom to lower.
Only the boom I control valve functions during the BOOM LOWER operation. Only oil from the right pump is supplied for this operation.
Reference: For further information on the main control valve, refer to Systems Operation, "Main Control Valve".
Boom Raise
When the pilot valve (joystick) is moved backward, pilot oil (C) shifts the spool of boom I control valve (1) downward. Oil is routed from the pump (4) to the main control valve (3). The pump receives oil from the hydraulic tank through the hydraulic line (D). The supply oil flows to the head end of the boom cylinder (2) through boom I control valve. This causes the cylinder rod to extend. The extending of the cylinder rod causes the boom to raise.
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| Illustration 2 | g00835183 |
Boom I control valve (BOOM RAISE) (1) Cylinder port (2) Load check valve (3) Hydraulic tank port (4) Passage (5) Pilot port (6) Hydraulic tank passage (7) Center bypass passage (8) Pilot passage | |
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| Illustration 3 | g00835200 |
Boom II control valve (BOOM RAISE) (9) Swing pump port (10) Load check valve (11) Passage (12) Hydraulic tank port (13) Pilot port (14) Hydraulic tank passage (15) Center bypass passage (16) Drain port | |
Both the boom I control valve and the boom II control valve function during the BOOM RAISE operation. Pump oil from the right pump and the swing pump combines with each other. The combined oil is delivered to the head end of the boom cylinder in order to raise the boom at a high speed.
The boom I control valve is equipped with a boom drift reduction valve. This valve acts as a check valve to prevent backflow of oil from the head end of the boom cylinder when the boom control valves are in the NEUTRAL or HOLD position.