The Mini Excavator Made in China continuously deviated during construction (deviated to the right when moving forward and backward), the whole machine had no abnormal sound and peculiar smell, and during excavation, the right side was weak and the left side was normal, so it was shut down for inspection at the construction site.

1. Failure cause analysis

The fault causes of traveling deviation of small excavator are mainly related to hydraulic pump and its control system, traveling control valve, central swivel, traveling motor and its control system, final drive system and track tension. If the sealing ring of the central rotary joint is damaged, it will cause mutual collusion of oil circuits and oil leakage, resulting in walking weakness. It can also lead to inconsistent speed of walking motors on both sides due to pressure oil leakage during walking, resulting in walking deviation fault of small excavator. If dirt blocks the small hole of the balance valve in the parking brake oil circuit and the parking brake cannot be released, it will also lead to walking deviation fault. If the travel motor safety valve leaks oil, the pressure in the travel system will be too low,which will reduce the speed of the travel motor, resulting in Travel Deviation fault.
Fault analysis and elimination of small excavator traveling deviation

2 troubleshooting

The “sequential troubleshooting method” is adopted for troubleshooting, that is, the troubleshooting is carried out item by item in the order of “mechanical part first and then hydraulic system”.

1) Check the mechanical part

First, check whether the tension of the tracks on both sides is consistent. Test results: the tension of tracks on both sides is within the standard range. Secondly, check the travel deceleration part. Since the machine moves forward and backward during operation, the power transmission between the traveling motor and the traveling driving wheel is relatively normal, the oil level and oil quality of the lubrication system are normal, and the mechanical structure is not damaged, the possibility of failure of the traveling deceleration part can be eliminated.

2) Check the hydraulic system

Taking the central rotary joint connecting the upper rotating body and the lower traveling body pipeline of the small excavator as the watershed, the “sequential troubleshooting method” is also used for troubleshooting, that is, troubleshooting is carried out item by item from bottom to top and from motor to pump.
(1) Check the travel motor. The four high-pressure oil pipes of the left and right travel motors were exchanged at the central swivel, and then the machine was tested. It was found that the deviation shifted from the right to the left, so the possibility of failure of the right travel motor and final drive was ruled out.
(2) Check the center swivel. In the traveling hydraulic system, the central rotary joint plays a very important role. It connects the upper rotating body of the small excavator with the pipeline of the lower walking body, so as to realize the walking and rotating functions of the small excavator. Connect the main control valve to the central rotary joint, and exchange the four oil supply hydraulic pipes that travel left and right. Then test the machine, and it is found that the deviation direction also changes, so the possibility of failure of the central rotary joint is eliminated.
(3) Check the hydraulic pump and its control system. If the hydraulic pump does not work normally, it will affect all the actions of the machine. During operation, except walking, other actions of the machine are normal, and the monitor shows that the hydraulic pump pressure is normal; Measure pump pressure: when there is no walking action, the pressure of the left pump is the same as that of the right pump. When walking, the pressure of the right pump is slightly lower than that of the left pump. All these show that the hydraulic pump and its control system are intact, thus eliminating the possibility of hydraulic pump failure.
(4) Check the travel control valve. The inspection found that the valve core of the right travel control valve did not move flexibly in the valve body, and the valve core was stuck. Disassemble and inspect the right travel control valve, and it is found that the spring in the main valve is broken. So far, it is determined that the cause of the fault is that the spring in the main valve of the right travel control valve is broken, resulting in the decrease of the oil pressure of the right travel system, resulting in the decrease of the speed of the right travel motor, which eventually leads to the right deviation of the travel direction.
Fault analysis and elimination of small excavator traveling deviation

3 repair scheme

(1) Replace the spring and relevant seals in the main valve of the right travel control valve.
(2) Clean the right travel control valve. After reassembly, test the machine and the fault disappears.

4 Conclusion

(1) When troubleshooting, consider first checking the right travel control valve to avoid detours.
(2) When repairing the right travel control valve, check the spring and valve core in the left travel control valve at the same time to avoid similar faults on the left.