Created on:2021-08-25 13:43

Fault diagnosis and maintenance of forklift hydraulic_ Forklift hydraulic system failure

Fault diagnosis and maintenance of forklift hydraulic_ Forklift hydraulic system failure

The lifting mechanism of CPCD30 forklift truck of a company had two similar failures: the lifting speed of no-load and full load was normal, but the descending speed was slow. After inspection, the inner and outer gantry and the bearings between them operate normally, and it is preliminarily judged that the hydraulic system is faulty.

It can be seen from figure L that after the high-pressure oil from the main reaches the multi-way valve, one part is diverted to the lifting hydraulic cylinder or tilt hydraulic cylinder, and the other part is diverted to the hydraulic steering gear control steering hydraulic cylinder with constant flow. When the lifting slide valve is pulled, the high-pressure oil flows under the piston of the lifting hydraulic cylinder through the one-way throttle valve and pushes the piston rod to complete the lifting action; When the lifting slide valve is pushed, the lower part of the piston of the lifting hydraulic cylinder is connected with the low pressure, and the piston rod is lowered by self weight and cargo weight. At this time, the oil flowing out of the lifting hydraulic cylinder is controlled by the one-way throttle valve.

It can be judged that the oil source system is normal by the normal action speed and lifting speed of the tilt hydraulic cylinder, that is, the main overflow valve and flow valve are normal, and the seal of the lifting hydraulic cylinder is not invalid.

After lifting the lifting hydraulic cylinder to a certain height without load, slowly loosen the high-pressure oil pipe joint of the lifting hydraulic cylinder at the multi-channel valve end, and the fault still exists, so the fault of the multi-channel valve can be eliminated. Similarly, after raising the lifting hydraulic cylinder to a certain height without load, slowly loosen the high-pressure oil pipe joint at the end of the one-way throttle valve, and the fault still exists, so the fault of the one-way throttle valve can be eliminated. Therefore, the fault section shall be concentrated on the shut-off valve of the right lifting hydraulic cylinder, which is used to prevent the accidental rupture of the high-pressure oil pipe from causing the sharp drop of the fork and goods, resulting in cargo damage and personal injury.

The working principle of the shut-off valve is: during normal operation, the oil from the lifting hydraulic cylinder passes through the shut-off valve spool, and the oil hole around the spool generates a pressure difference in the chamber of spool 2. When the pressure difference is less than the spring force, the spool does not act, and the lowering speed of the piston rod of the lifting hydraulic cylinder is controlled by adjusting the opening of the orifice of the one-way throttle valve to make it within the normal lowering speed. When the high-pressure oil pipe breaks suddenly, a large pressure difference is formed in the chamber of slide valve 2, and the slide valve moves to the left, so as to block the oil hole around it. Only a small amount of oil flows through the small hole at the end of the slide valve, so that the fork drops slowly to achieve the purpose of safety protection.

It can be seen that the root cause of the above faults is that the slide valve of the shut-off valve moves to the left during descent and blocks the oil holes around it. If the rising speed is normal, it means that the slide valve can move smoothly. The left movement of the slide valve is not caused by jamming, but caused by the break of the slide valve spring or plastic softening. After removing the slide valve spring and adding a washer, the faults of the hydraulic system of two CPCD30 forklifts were successfully eliminated.

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