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| Illustration 1 | g00749200 |
Hydraulic schematic of pump system (1) Left travel motor (2) Right travel motor (3) Swing motor (4) Bucket cylinder (5) Boom cylinder (6) Stick cylinder (7) Blade cylinder (8) Swing cylinder (9) Swivel (10) Shock reducing valve (11) Blade control valve (12) Main control valve (13) Pilot control valve (swing boom) (14) Boom drift reduction valve (15) Main relief valve (16) Pilot control valve (travel) (17) Pilot control valve (blade) (18) Pilot control valve (swing and stick) (19) Pilot control valve (boom and bucket) (20) Accumulator (21) Pilot oil manifold (22) Slow return check valve (23) Bypass check valve (24) Oil cooler (25) Right pump (26) Left pump (27) Pilot pump (28) Swing boom/blade pump (29) Solenoid valve (travel speed) (30) Hydraulic activation control valve (31) Hydraulic tank (32) Pilot relief valve (33) Pilot filter | |
Hydraulic Pump Flow and Pressure Control System
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| Illustration 2 | g00749321 |
Pump compartment (27) Pilot pump (28) Blade pump (43) Main pump | |
This machine is driven and controlled by the following three systems.
- The main hydraulic system supplies oil to the cylinders and motors of the machine.
- The blade hydraulic system supplies oil to the blade circuits.
- The pilot hydraulic system supplies oil to the control circuits.
The main hydraulic system oil is supplied by main pump (43). Main pump (43) is a single piston type pump and the main pump is a variable displacement piston pump. The single main pump functions in the same manner as a double pump by separating the pump oil flows into the right and left circuits. Separation of pump flow into the two circuits is done by the activation of the pistons in the cylinder block.
Note: Throughout this manual, the portion of the pump that supplies oil flow to the right circuits will be described as the right pump. The portion of the pump that supplies oil flow to the left circuits will be described as the left pump.
Right pump (25) supplies oil flow to the right control system of the main control valve (12). Left pump (26) supplies oil flow to the left control system of the main control valve (12). The main pump is mechanically connected to the engine through the flexible coupling.
Blade pump (28) is a gear type pump. The blade pump supplies oil to the hydraulic system for the blade. Pilot pump (27) is a gear type pump and the pilot pump is directly connected to rear of the blade pump (28). The pilot pump drives the pilot hydraulic system. All engine output is used to drive these three pumps.
When the load increases, the main pump increases the delivery pressure and the main pump decreases the flow rate. The system maintains constant hydraulic horsepower. The engine is maintained at the full available horsepower. See Systems Operation, "Pump Control (Main Hydraulic)".
Right pump (25) delivers oil flow to the right side of main control valve (12). Left pump (26) delivers oil flow to the left side of main control valve (12). The pump oil flows through the main control valve and the oil flow returns to hydraulic tank (31) when no work is being performed.
During machine operation, main control valve (12) directs pump oil to the respective cylinders (boom, bucket, and stick) and/or motors (swing and travel). Main control valve (12) contains numerous valve stems, relief valves, 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 restricted by main relief valve (15). The pressure setting of the main relief valve is 31400 kPa (4550 psi) during travel operation and 27500 kPa (4000 psi) during implement operation or during swing operation.
Pilot pump (27) delivers a constant flow to the pilot circuit regardless of oil pressure. The operating pressure of the pilot circuit increases to the pressure setting of pilot relief valve (32). The pressure setting of the pilot relief valve is 3450 kPa (500 psi).
Note: Refer to Systems Operation, "Pilot Hydraulic System" for more information concerning pilot control operation.
Blade Control Valve
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| Illustration 3 | g00752779 |
Blade control valve (58) Blade relief valve (59) Inlet line | |
Supply oil from blade pump (28) enters blade control valve (11) through inlet line (59). When the blade control lever is in the NEUTRAL position, the oil flows through blade control valve (11) and the oil flow returns to hydraulic tank (31) .
The pressure setting for blade relief valve (58) is 24500 kPa (3550 psi). This is the maximum working pressure of the hydraulic system for the blade circuit.