1. Pilot control oil circuit diagram and cut-off position table for measurement
The pilot control oil circuit is shown in Figure 1-3. The cut-off area for measurement is shown in Table 1-15.
2. Fault diagnosis and troubleshooting
(1) First check whether the overflow pressure of the pilot pump is normal (engine operates at no load and high speed with overflow pressure of 3.281 MPa). If the measured value is lower than the specified value, measure the overflow pressure step by step according to the cut-off position shown in Table 1-15. If the overflow pressure is within the specified range, it means that the leakage in the truncated component is too large and should be repaired or replaced. If the overflow pressure is still below the specified value, check the pilot pump outlet screen for foreign matter.
(2) If there is foreign material in the outlet screen of the pilot pump, it means that the pilot pump is faulty; if there is no foreign material, it means that the relief valve of the pilot pump is faulty and the fault can be eliminated after replacement.
(3) If the overflow pressure of the pilot pump is in the range of 3.2-1MPa at the beginning of inspection, check whether the overflow pressure of the front and rear hydraulic pumps is normal (in mode H, working mode H.O, measured at no-load high-speed operation of the engine, when normal overflow occurs, the overflow pressure is 31-34MPa; when secondary overflow occurs, the overflow pressure is 32.5-36.5MPa).
(4) If the overflow pressure of the front and rear hydraulic pumps is lower than the standard value, adjust the main relief valve and measure the overflow pressure of the front and rear hydraulic pumps after adjustment. If the overflow pressure returns to normal, the fault has been remedied; if the overflow pressure still does not reach the standard value, the main relief valve is faulty and the fault can be remedied after repair or replacement.
(5) If the overflow pressure of the front and rear hydraulic pumps is in the range of 31-34 MPa, continue to check whether the setting pressure of TVC valve (torsion control valve) is normal (working mode is H.0, mode is H, engine runs at no-load and high speed, No. 1 hydraulic pump overflows and setting pressure is (1.4 <0.1) MPa).
(6) If the set pressure of TVC valve is not within the specified range, adjust the IVC valve. If it returns to normal after adjustment, the fault will be eliminated; if it does not return to normal after adjustment, the TVC valve is faulty and the fault will be eliminated after repair or replacement.
(7) If the set pressure of TVC valve is within the specified range, observe whether the engine speed is normal when the hydraulic pump overflows with the cancellation of CO valve (working mode is H.O, mode is H, engine runs at no load and high speed, bucket rod overflows, CO valve cancels, engine speed is (2050 + 60) r/min).
(8) If the hydraulic pump overflows with the cancellation of CO valve and the engine speed is within the specified range, the cause of the fault is that the internal leakage of the hydraulic pump is too large. After repairing or replacing a new pump, the fault can be eliminated. If the engine speed is not within the specified range, it may be indicated that there is a fault in the engine fuel system, and the relevant excavator repair should be carried out.
