The handling of the automatic forward tilt of the loader's bucket

one Fault phenomenon: A loader of a certain company suddenly experienced weak operation of the bucket and automatic forward tilting after reaching the position during use. However, the rise and fall of the boom were normal during operation.

two The hydraulic principle is shown in the figure

The main components of the hydraulic system include: oil tank, oil pump, distribution valve, boom cylinder, bucket cylinder, oil pipe, etc.

When the working device is not in operation, the hydraulic oil from the oil pump is input into the working distribution valve and returns to the oil tank through the return oil chamber of the distribution valve. When it is necessary to dig or unload materials with the bucket, operate the bucket control lever, pull it backward or push it forward. The working oil from the oil pump enters the rear or front chamber of the bucket cylinder through the distribution valve, causing the bucket to flip up or down. When it is necessary to lift or lower the boom, operate the boom control lever, pull it back or push it forward. The working oil from the oil pump enters the lower or upper chamber of the boom cylinder through the distribution valve, thereby lifting or lowering the boom and bucket. When the bucket needs to float up and down (for loading and unloading bulk materials), push the control lever of the boom to the floating position. The working oil from the oil pump can enter the upper and lower chambers of the boom cylinder through the distribution valve and be connected to the oil tank at the same time. The working oil in the upper and lower chambers of the cylinder is in a low-pressure state, and the bucket is in a free floating state under its own weight, working close to the ground. When the bucket encounters external impact loads or interference from other mechanisms, the overload valve in the double-acting safety valve opens to provide safety protection. The oil replenishment valve in a double-acting safety valve serves to replenish oil by preventing a certain cavity of the cylinder from being sucked empty.

Three Cause analysis and handling

Based on the principle analysis, it is believed that the following possible reasons may lead to the occurrence of the above phenomenon:

"a. The oil seal in the bucket oil cylinder is damaged. "b. The oil circuit for the forward tilt of the rotating bucket in the distribution valve is damaged

"c The bucket slide valve and the bucket double-acting safety valve in the distribution valve have malfunctioned.

If the oil seal in the bucket cylinder is damaged, under the action of the bucket, the oil in the large cavity will flow into the small cavity (the cavity with a rod), which may cause the bucket to automatically tilt forward. After disassembling the two rotating bucket cylinders, it was found that one cylinder was normal, while the oil seal of the other cylinder was severely damaged. However, after the oil cylinder was replaced, the bucket still automatically leaned forward.

If the forward tilt oil circuit of the rotating bucket in the distribution valve is damaged, causing the oil in the forward tilt oil circuit of the rotating bucket to flow into the oil tank, it will also lead to the automatic forward tilt of the rotating bucket. Check the slide valve of the bucket and find that it is in a normal state.

If the double-acting safety valve of the rotating bucket is in the always open state, it can also cause the rotating bucket to automatically tilt forward. Because the large and small cavity double-acting safety valves of the bucket are used to prevent overload and replenish oil in the small cavity of the bucket. After disassembling and inspecting the double-acting safety valve, it was found that there was a small black rubber block at the front end of the cone valve. After identification, it was determined that this small black rubber block was a remnant of the damaged oil seal of the rotary bucket cylinder. Under normal circumstances, the cone valve should be closed. Currently, a small rubber block is at the front end of the cone valve, pushing it open to keep it in an open state, causing the bucket cylinder to unload, the piston rod to retract, and through the connecting rod mechanism, the bucket automatically tilts forward.

Finally, remove the small rubber block from the double-acting safety valve of the rotating bucket, and the bucket will no longer tilt forward automatically.