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| Illustration 1 | g00489464 |
Hydraulic schematic for pilot system (1) Solenoid valve (swing parking brake) (2) Swing parking brake (3) Displacement change valve (left travel) (4) Displacement change valve (right travel) (5) Stick drift reduction valve (6) Control valve (left travel) (7) Control valve (straight travel) (8) Main control valve (9) Pressure switch (implement and swing) (10) Pressure switch (travel) (11) Control valve (right travel) (12) Control valve (boom I) (13) Boom drift reduction valve (14) Logic valve (15) Main relief valve (16) Pressure control valve (17) Pressure switch (boom raise) (18) Pilot control valve (left and right travel) (19) Pilot control valve (stick and swing) (20) Pilot control valve (bucket and boom) (21) Solenoid valve (fine control) (22) Solenoid valve (travel speed) (23) Solenoid valve (swing priority mode) (24) Proportional reducing valve (25) Pilot manifold (26) Hydraulic activation control valve (27) Pilot relief valve (28) Upper pump (29) Lower pump (30) Pilot pump (31) Pilot filter | |
Pilot Pump
Pilot pump (30) is a gear type pump and the pump is mechanically connected to the lower pump. The pilot pump supplies pressure oil to the pilot hydraulic system. When there is no load on the engine, the output flow from the pilot pump is approximately 46 L/min (12.1 US gpm).
Pilot Oil Circuit
Pilot system oil from pilot pump (30) has the following three main functions:
- Control main pump output.
- Operate the control valves.
- Create pilot oil pressure in order to achieve various operations.
The pilot oil from pilot pump (30) goes through pilot filter (31). The pilot oil then enters pilot oil manifold (25). The pilot oil is then separated into the following circuits:
- Proportional reducing valve
- Pilot control valve
- Main control valve
- Swing parking brake release
- Logic valve
- Automatic travel speed
Proportional Reducing Valve Circuit
Pilot oil flows to proportional reducing valve (24). The proportional reducing valve changes the pilot oil into a hydraulic signal. This hydraulic signal is called power shift pressure. The hydraulic signal flows to the regulators of main pumps (28) and (29). The hydraulic signal controls the pump output.
Pilot Control Valve Circuits
Pilot control valve circuits direct pilot pump oil to hydraulic activation control valve (26). Pilot oil then goes to the following pilot control valves: (18) left and right travel, (19) stick and swing and (20) bucket and boom.
When a pilot control valve is operated, pilot oil goes to the main control valve that is selected. The pilot oil shifts the stem of the selected main control valve in order to operate a cylinder and/or a motor.
Main Control Valve
Pilot oil flow to the main control valve flows to pressure switch (9) and pressure switch (10) .
Travel pressure switch (10) is located on main control valve (8). An increase in pilot oil pressure causes pressure switch (10) to change to the ON position. When the machine does not travel, the pilot oil pressure is low and switch (10) is OFF. The signal from travel pressure switch (10) is sent to the electronic controller. The electronic controller processes the signal from travel pressure switch (10) and the signal from pressure switch (9) so the automatic engine speed control (AEC) functions.
The pilot oil pressure increases when the right and left control valves are operated at the same time. The pressure increase activates straight travel control valve (7) so the machine can travel straight during a combined operation.
When a swing and/or implement control is operated, the pilot oil pressure increases. The increased oil pressure turns on pressure switch (9). When no implement and swing controls are operated, the pilot oil pressure remains low. The pilot oil pressure does not activate pressure switch (9) .
Swing Parking Brake Release (Circuit)
The circuit for the swing parking brake release releases the swing parking brake during implement operation and/or swing operation. Pilot oil flows to solenoid valve (1). Pilot oil from pilot manifold (25) flows through hydraulic activation control valve (26) to solenoid valve (1). When the implement controls and/or swing controls are operated, the increase in pilot oil pressure causes solenoid valve (1) to change to the open position. The pilot oil flows through solenoid valve (1) to swing parking brake (2). This releases the swing parking brake.
Logic Valve (Circuit)
Pilot oil goes through solenoid valve (23) to pressure control valve (16). Pressure control valve (16) activates to open logic valve (14). Upper pump oil flows to the swing circuit and the stick circuit.
Automatic Travel Speed Change Valve Circuit
Pilot oil flows to travel speed solenoid valve (22). When the switch for the travel speed is placed in the HIGH SPEED position, travel speed solenoid valve (22) opens. The pilot oil flows through travel speed solenoid valve (22) to right and left travel displacement change valves (4) and (3). Valves (4) and (3) activate so the machine travels in an optimum speed.