Bucket dropping failure of small loader: when the operating handle of the pilot valve is in the middle position, the bucket will automatically tilt forward, that is, the bucket will drop.
Fault analysis: according to the linkage mechanism of the working device, when the bucket is in the retracted state and the operating handle of the pilot valve is in the middle position, the large cavity of the bucket rotation cylinder is under pressure due to the dead weight of the bucket; At this time, as long as the pressure oil in the large chamber leaks relative to the return port, the bucket will automatically tilt forward.
There are six ways to cause the leakage of oil from the large cavity of the rotary bucket cylinder to the oil return port:
First, the pipe fittings, joints and installed joint surfaces between the large chamber of the bucket cylinder and the distribution valve have obvious leakage.
Second, the valve rod of the rotary bucket reversing valve of the distribution valve failed to return to the middle position (due to the stuck valve rod of the reversing valve, the valve core of the rotary bucket large-chamber pilot valve failed to reset due to the sticking, and the valve body of the rotary bucket large-chamber pilot valve had sand hole internal leakage, etc.), making the small cavity of the rotary bucket oil cylinder connected with the pump port and the large cavity connected with the oil return port.
Third, when there is internal leakage in the bucket cylinder, there is also leakage in the bucket chamber relative to the oil return port.
Fourth, the pressure of the overload valve in the large chamber of the rotary bucket oil cylinder is too low (caused by the broken pressure regulating spring, dirt stuck in the open position of the valve core, sand holes or grooves on the valve body that are connected with the oil return chamber, etc.).
Fifthly, there is leakage in the large chamber oil make-up valve of the rotary bucket cylinder (caused by the broken return spring, the dirt stuck in the open position of the valve core, the dirt or groove defect on the connecting cone of the valve core and the valve body, and the sand hole on the valve body is connected with the oil return cavity).
Sixth, the excessive wear of the reversing valve core or valve hole makes the fitting clearance between the valve core and the valve hole far greater than the design value, resulting in pressure oil leakage in the large chamber of the rotary bucket cylinder.
The troubleshooting of bucket dropping should be carried out around the following six leakage ways:
① Around the above six leakage situations, the simplest and easiest to judge is the first one: start the small loader, lift the boom to a certain height, and retract the bucket to the maximum position, and observe whether the pipe fittings, joints, and installed joint surfaces between the large chamber of the bucket cylinder and the distribution valve have obvious leakage.
② If there is no external leakage in the first case, the second case can be judged: start the small loader and operate the handle of the pilot valve to lift the boom to the highest position and the bucket to the maximum position → the engine stops and remove the guide pipe at both ends of the distribution valve bucket valve rod. At this time, if the bucket dropping phenomenon disappears, it can be determined that the bucket dropping phenomenon is caused by the non-return of the distribution valve bucket rotation valve rod to the center due to the pilot valve, and the pilot valve should be disassembled and cleaned or replaced. Otherwise, the third case should be judged!
③ For the third case, we can make some simple judgments: start the small loader and operate the handle of the pilot valve to lower the boom to the lowest position and tilt the bucket back to the maximum position → stop the engine and open the large chamber hose of the bucket cylinder and lead it back to the hydraulic tank → start the engine and operate the handle of the pilot valve to tilt the bucket back → observe whether there is continuous hydraulic oil from the large chamber oil port of the bucket cylinder. If the hydraulic oil continuously emerges at this time, it indicates that there is serious internal leakage in the bucket cylinder, and the cylinder needs to be disassembled, repaired or replaced. If the oil cylinder has no internal leakage, the fourth and fifth cases should be further analyzed.
④ For the fourth and fifth cases, we can use the pressure detection method to determine: connect a pressure gauge with a range of 0~25MPa to the pressure tap of the large chamber of the bucket cylinder → start the machine → operate the handle of the pilot valve to make the bucket at the maximum forward tilt position → increase the oil valve and operate the handle of the pilot valve to lift the boom, while observing that the reading of the pressure gauge during the boom lifting process should reach the design value (22MPa). Otherwise, one or both of the two leakage cases are true, and the overload valve or oil make-up valve of the large chamber of the bucket cylinder should be disassembled, inspected and cleaned.
⑤ If the bucket dropping phenomenon does not disappear after the first to fifth conditions are eliminated, stop the machine, lower the boom and bucket to the lowest, disassemble the bucket valve rod of the distribution valve, and carefully check the valve rod and valve hole and their matching conditions.