Forklift maintenance case studies

• ‌Cannot ascend/descend‌: First, check if the wiringis worn out, especially the wiring passing through the rotating parts (such asthe handle to the control box). Then, check if the solenoid valve is energizedand if the limit switch is stuck.

• ‌Cannot move forward/backward‌: Mainlycheck if the wiring of the control module is broken. Then, check if thesteering switch is damaged.

• ‌Transmission problem‌: Difficulty in shifting gears may be due to insufficient pressureor slipping clutch. Check the oil pump, sealing ring, friction plate, etc. Ifthe transmission is overheating, check the oil quantity, oil quality andcooling system. •

‌Fault Phenomenon‌:

During operation, the forklift deviatedfrom the intended direction. The dashboard's steering indicator light flashed,accompanied by high-frequency vibrations of the hydraulic pipes, and theresistance when operating the steering wheel significantly increased.

‌Diagnosis Process‌:

1.    ‌Basic Inspection‌: Confirm that the hydraulic oil level is normal, the oil is notemulsified or deteriorated, and the chassis has no collision marks.

2.    ‌Pressure Test‌: Use a dedicated pressure gauge to detect the output pressure ofthe steering assist pump. It was found that the pressure fluctuated beyond thestandard range (the normal value should be stable at 8-10 MPa, while themeasured fluctuation reached 12-14 MPa).

3.    ‌Component Inspection‌: Disassemble the steering assembly and found that the matingsurface of the sector gear was abnormally worn, and the steering valve core wasstuck.

‌Maintenance Plan‌:

•      Replacethe sector gear set and steering valve assembly, and clean the hydrauliccircuit.

•      Adjustthe gap between the steering unit and the steering wheel to the standard value(0.5-1mm).

•      Replacethe hydraulic oil and evacuate it, and test the steering assist pressure torestore it to 9.5 MPa.

‌Root Cause‌:

Long-term overloading operation led to wearinside the steering unit, and the hydraulic oil contamination exacerbated thevalve core sticking, ultimately causing the system pressure to lose control.

‌Preventive Measures‌:

•      Replacethe hydraulic oil and filter element every 500 hours.

•      Regularlycheck the meshing clearance of the steering gear, and avoid sharp turningoperations.

‌Fault phenomenon‌:

The mast cannot rise. When operating thelifting handle, the hydraulic pump shows no response. The motor is running butthere is no pressure output.

‌Diagnosis process‌:

1.    ‌Electrical inspection‌: Measured the power supplyvoltage of the lifting motor to be normal (24V), and the control signal linewas found to be without any breakage.

2.    ‌Hydraulic test‌: Cut off the oil inlet pipe of the rising cylinder, and whenoperating the handle, no oil flowed out. It was confirmed that the pump was notworking.

3.    ‌Pump body disassembly‌: It was found that thehydraulic pump was severely worn and the plunger spring was broken, resultingin the inability to establish pressure.

‌Maintenance plan‌:

•      Replacethe hydraulic pump assembly, clean the oil tank and pipelines.

•      Adjustthe multi-way valve relief valve to the set pressure (14MPa).

•      Testthe lifting speed and stability of the mast, which meet the standards(empty-load rising time ≤ 12 seconds).

‌Root cause‌:

The hydraulic oil has not been replaced fora long time, and impurities have caused wear on the pump body, and overpressureoperations have accelerated the aging of components.

‌Preventive measures‌:

•      Establishan oil contamination degree detection system, take samples for analysis every 3months.

•      Avoidoverloading the mast and rapid descent when operating.

‌Fault symptoms‌:

The starting motor operates normally, butthe engine fails to ignite and there is no smoke emitted from the exhaust pipe.

‌Diagnosis process‌:

1.    ‌Fuel system inspection‌: The hand pump delivers fuelnormally, and the atomization test of the fuel injector is good.

2.    ‌Air circuit test‌: The air filter is not clogged, and there is no leakage in theintake pipe.

3.    ‌Ignition investigation‌: The spark plugs wereremoved and it was found that the electrodes were severely carbonized, and theresistance value of the ignition coil was abnormal.

‌Maintenance plan‌:

•      Replacethe spark plugs and ignition coil, and clean the throttle valve.

•      Adjustthe valve clearance to 0.2mm (cold state).

•      Testthe starting time to be shortened to within 3 seconds and ensure smoothoperation.

‌Root cause‌:

The spark plugs were not replaced beyondtheir usage period, and the insufficient ignition energy led to carbon depositsin the combustion chamber.

‌Preventive measures‌:

•      Inspectthe spark plug condition every 200 hours and force replacement every 500 hours.

•      Usefuel that meets specifications and avoid long-idle operation. •

1.‌ Diagnostic Priority‌: Electrical system (40% failure rate) > Hydraulic system (35%)> Mechanical structure (25%).

2.‌ Safety Regulations‌: Before maintenance, power must be cut off and oil supply stopped,and warning signs must be hung; for high-altitude operations, safety belts mustbe worn.

3.‌ Data Recording‌: It is recommended to establish a maintenance file, recording faultcodes, replaced parts, and test parameters.