During the construction process of the ZL40 loader, the boom gradually automatically sinks, and as the oil temperature increases, the amount of subsidence increases. As a rule of thumb, the cause of this fault should be on the boom cylinder or work unit distribution valve. Then, after starting the engine, let the loading boom rise to its highest position and use the crane to lift the boom and hold it in the highest position. After turning the boom lever to the neutral position, turn off the engine, and then remove the two tubing of the two boom cylinders into the oil pan, and then start the engine, pull the joystick lever to the raised position, and properly increase At the engine speed, we can clearly see that there is a large amount of oil flowing out from the small boom of the left boom cylinder, and there is almost no oil flow out from the tubing of the right boom cylinder. This means that the boom sinking is caused by the inner side of the left boom cylinder. After the engine stalls, carefully remove the left-side boom cylinder assembly, clean and disassemble. When the piston rod assembly was pulled out, it was found that the Y-ring of the large cavity end of the piston hardened and a layer had fallen off at the lip of the oil seal. All the seals were cleaned and replaced. When the test machine was refitted, the boom self-sinking phenomenon improved slightly, but it was not completely removed.
Upon inspection, the small cavity of the hydraulic cylinder also has an oil return phenomenon. Obviously, this is the oil seal is not installed. Then dismantling and dismantling again, it was found that a 4 mm long section was cut off at the lip of the large cavity oil seal, and the large cavity could not be completely sealed. When the boom was lifted, a small part of the pressure oil leaked into the small cavity. In the neutral position, due to the weight of the boom and the weight of the bucket and the material, there is still a certain pressure in the large cavity of the boom cylinder, from which the oil leaks into the small cavity, causing the boom to automatically sink.
Replace the oil seal again, replace the test machine, and the phenomenon of automatic sinking of the boom has not been completely eliminated. This indicates that the oil seal that was replaced for the second time is still not assembled. In general, before the assembly of the hydraulic cylinder of this structure, as long as the rust and burrs of the guide sleeve inside the cylinder tube are removed, the assembly is relatively smooth and the quality is easy to ensure. To examine the causes of multiple assembly errors, disintegrate again. First, marks corresponding to the positions of the cylinders were engraved on the piston rod earrings, and then decomposed. After slowly pulling out the piston rod assembly, it was found that the size and shape of the large cavity oil seal were the same as those of the previous one. Align the engraved mark, observe the positional relationship between the damaged part of the oil seal and the cylinder, and find that this part is in a straight line with the position of the inlet port of the hydraulic cylinder's small chamber, which indicates that a certain part of the cylinder is on this line. Damaged seals have caused the seal to be scratched during assembly. Check the cylinder tube, the inner wall is smooth and no damage. It seems that the possibility of damage to the oil inlet of the small chamber is relatively large, and the hand feels a scratching feeling. After grinding the oil hole, smooth the chamfer of the hole. After cleaning, replace the damaged oil seal and reassemble it. When the large cavity Y-shaped seal ring passes through the oil inlet of the small cavity, use a flat-head screwdriver to care. Place the seal against the outwardly rising oil seal lip so that it smoothly passes through the oil hole. After loading the test machine, the boom automatically disappeared.
Upon inspection, the small cavity of the hydraulic cylinder also has an oil return phenomenon. Obviously, this is the oil seal is not installed. Then dismantling and dismantling again, it was found that a 4 mm long section was cut off at the lip of the large cavity oil seal, and the large cavity could not be completely sealed. When the boom was lifted, a small part of the pressure oil leaked into the small cavity. In the neutral position, due to the weight of the boom and the weight of the bucket and the material, there is still a certain pressure in the large cavity of the boom cylinder, from which the oil leaks into the small cavity, causing the boom to automatically sink.
Replace the oil seal again, replace the test machine, and the phenomenon of automatic sinking of the boom has not been completely eliminated. This indicates that the oil seal that was replaced for the second time is still not assembled. In general, before the assembly of the hydraulic cylinder of this structure, as long as the rust and burrs of the guide sleeve inside the cylinder tube are removed, the assembly is relatively smooth and the quality is easy to ensure. To examine the causes of multiple assembly errors, disintegrate again. First, marks corresponding to the positions of the cylinders were engraved on the piston rod earrings, and then decomposed. After slowly pulling out the piston rod assembly, it was found that the size and shape of the large cavity oil seal were the same as those of the previous one. Align the engraved mark, observe the positional relationship between the damaged part of the oil seal and the cylinder, and find that this part is in a straight line with the position of the inlet port of the hydraulic cylinder's small chamber, which indicates that a certain part of the cylinder is on this line. Damaged seals have caused the seal to be scratched during assembly. Check the cylinder tube, the inner wall is smooth and no damage. It seems that the possibility of damage to the oil inlet of the small chamber is relatively large, and the hand feels a scratching feeling. After grinding the oil hole, smooth the chamfer of the hole. After cleaning, replace the damaged oil seal and reassemble it. When the large cavity Y-shaped seal ring passes through the oil inlet of the small cavity, use a flat-head screwdriver to care. Place the seal against the outwardly rising oil seal lip so that it smoothly passes through the oil hole. After loading the test machine, the boom automatically disappeared.
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