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| Illustration 1 | g03506869 |
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(1) Boom cylinder
(2) Stick cylinder (3) Bucket cylinder (4) Left travel motor (5) Right travel motor (6) Swivel (7) Swing motor (8) Main control valve (9) Pilot control valve (swing and stick) (10) Pilot control valve (boom and bucket) (11) Pilot control valve (travel) (12) Main pump (13) In-line filter (14) Travel speed solenoid valve (15) Hydraulic activation solenoid valve (16) Pilot manifold (17) Accumulator (18) Hydraulic tank (19) Oil cooler (20) Bypass check valve (21) Slow return check valve (22) Proportional reducing valve (23) Main supply line (24) Parallel feeder passage (25) Return line (26) Proportional pressure compensator (27) Blade cylinder (28) Swing boom cylinder (29) Solenoid valves (30) Pilot control valve (blade) | |
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| Illustration 2 | g03344578 |
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Pump compartment (12) Main pump (23) Delivery line (main pump) | |
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| Illustration 3 | g03344576 |
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Main control valve (8) Main control valve | |
This machine is driven and controlled by the following systems.
- The main hydraulic system controls the cylinders, the travel motors, and the swing motor.
- The pilot hydraulic system supplies oil to the pilot control valves, swing brake, and the travel motors.
The main hydraulic system delivers oil flow from main pump (12) in order to control the following components: boom cylinder (1), stick cylinder (2), bucket cylinder (3), blade cylinder (27), boom swing cylinder (28), left travel motor (4), right travel motor (5) and swing motor (7).
Main pump (12) is a variable displacement, pressure compensated piston pump. Main pump (12) is directly connected to the engine by a flexible coupling. Main pump (12) delivers oil to main control valve (8) and supplies oil to the pilot hydraulic system. All engine output is used to drive main pump (12).
As the load pressure increases during working conditions, the delivery pressure increases and the oil flow rate will decrease. The hydraulic horsepower remains constant even though the delivery pressure and the flow rates change. The hydraulic horsepower is almost identical to the engine horsepower.
When no work is being performed, pump oil flows from main pump (12) and through main supply line (23). The oil then flows into main control valve (8). Oil from main supply line (23) flows through parallel feeder passage (24), pilot manifold (17), return line (25) and back to hydraulic tank (18). Main control valve (8) sends a signal for flow control to proportional pressure compensator (26) located in main pump (12). The signal received by proportional pressure compensator (26) causes the pump to destroke to the minimum output flow.
If an operation is being performed, main control valve (8) directs pump oil to various components. These components are the cylinders (boom, bucket, and stick, blade, and boom swing) and/or motors (swing and travel). Main control valve (8) contains numerous valve stems, passages, check valves, and orifices in order to carry out a single operation or a combined operation. The working pressure of the main hydraulic system is sensed by proportional pressure compensator (26) in main pump (12).
The oil flow from main pump (12) is constant as the oil enters the pilot system. The maximum pressure of the pilot system is regulated by the pressure setting of proportional reducing valve (22).
For more information concerning the pilot hydraulic system, refer to Systems Operation, "Pilot Hydraulic System".