The pilot pump is equipped with an overflow valve that receives oil from the hydraulic tank through an oil suction filter.
The amount of oil discharged from the pilot pump flows into the remote control valve, EPPR valve (electromagnetic proportional pressure reducing valve), solenoid valve assembly, rotary parking brake, main control valve and safety lock solenoid valve through the pipeline filter.
1. Modern excavator oil suction circuit, oil transmission circuit and oil return circuit
The pilot pump receives the oil from the hydraulic oil tank, and then the pilot pump discharges the oil to the safety solenoid valve through the line filter, and the oil is filtered through the line filter. The pilot pump is equipped with a pilot relief valve to limit the pilot circuit pressure.
The oil passing through the pipeline filter flows to the remote control valve through the safety solenoid valve.
Return oil flows to the hydraulic tank.
2. Safety valve (safety joystick
When the operating lever of the safety solenoid valve moves downward, the oil flows into the remote control valve through the solenoid valve and the line filter. When the operating lever of the safety solenoid valve moves upward, oil does not flow into the remote control valve because the oil path is blocked
3. Boom priority system
When combined operation of swing and boom or arm, the operation speed of boom or arm is lower than normal speed. In order to increase the working efficiency, a rotary deceleration system is used. When the heavy-duty operating mode is used, the pilot oil of the pilot pump flows through the solenoid valve into the Pns port in the main control valve. Pns oil pressure pushes the rotary deceleration spool to a lower position, and the oil flow to the rotary motor is reduced. Then, the boom or arm speed increases. This process is the Boom Priority System
4. Walking speed control system
When the travel speed switch is pressed, the travel speed solenoid valve is activated, and the oil flow discharged from the pilot pump travels to the pilot valve Pk port in the motor. As a result, the control plunger is pushed by the main oil flow, and the discharge volume reaches the minimum. When the travel speed switch is pressed again, the travel speed solenoid valve returns to the initial position due to the spring force, and the hydraulic oil at the Pk port returns to the hydraulic tank. As a result, the control plunger is pushed back by the main oil flow, and the discharge amount reaches the maximum.
5. Main overflow pressure lifting system
When the power lift switch of the left joystick is pressed to ON, the power lift solenoid valve is activated, and the discharge oil of the pilot pump flows into the main relief valve Pz port of the main control valve; then the pressure set by the main relief valve Increase from 330kgfm2 to 360kgcm2 to increase the digging force. If you continue to press the power lift switch, the command will be released after 8s
6. Maximum flow cut-off system
When the brake operation mode is selected, the maximum flow cutoff solenoid valve is automatically activated. Therefore, the pilot pressure (sent to the regulator, the pump discharge will be reduced
7、Release of swing parking brake
When the rotary control lever works, the pilot oil flows into the SH port of the shuttle valve, the pressure moves the spool, and the oil discharged from the pilot valve flows into the PG port.
Pressure is applied to the swing motor, so the brake is released. When the swing joystick is set to the middle position, the oil in the swing motor cylinder is discharged, so the brake is used.
