Created on:2021-10-07 10:13

Fault diagnosis and maintenance of loader hydraulic_ Three hydraulic faults of loader

Fault diagnosis and maintenance of loader hydraulic_ Three hydraulic faults of loader

ZL50 loader adopts a hydraulic system in which the energy of steering and working systems are converted to each other, as shown in Figure I. If the hydraulic components work poorly, the following three faults often occur in the working device of the machine.

I.jpg

(1) Weak boom lifting

The direct cause of boom lifting weakness is insufficient pressure oil at the piston end of boom hydraulic cylinder. The main reasons are:

① The oil filter is blocked or the internal leakage of the hydraulic pump is serious, and the oil with sufficient pressure cannot be pumped out;

Serious internal and external leakage occurs in the face hydraulic system. The position of internal leakage may be that the pressure adjustment of the main safety valve of multiplex Xingfa is too low, or the main valve core is stuck in the open position by dirt (the spring of the main valve core is very soft and easy to be stuck by dirt), and the clearance between the valve rod of the boom directional valve and the valve body hole in the multiplex valve is too large, The sealing ring on the piston of the boom hydraulic cylinder is damaged or severely worn, the gap between the valve core of the flow conversion valve and the valve body is too large, or the one-way valve in the valve is not tightly sealed.

The exclusion methods are as follows.

① Check the oil filter and clean or replace it if it is blocked; Observe the oil and replace it if it deteriorates.

② Check whether the main safety valve is stuck. If it is stuck, just remove the main safety valve and clean the main valve core so that it can be pushed freely. If the fault cannot be eliminated, operate the multi-way directional valve, rotate the pressure regulating nut of the main safety valve, and observe the pressure response of the system. If the pressure can be adjusted to the specified value, the fault is basically eliminated.

③ Judge whether the piston sealing ring of the hydraulic cylinder has lost its sealing function: close the boom hydraulic cylinder to the end, remove the high-pressure rubber hose at the outlet joint of the large chamber of the hydraulic cylinder, and continue to operate the boom reversing handle of the multi-way valve to make the boom hydraulic cylinder further retract the piston rod (because the piston rod has been closed to the end and can not move again, the oil pressure continues to rise). Then, carefully observe whether there is oil flow at the outlet of the large chamber of the hydraulic cylinder. If there is only a small amount of oil flow at the outlet of the large chamber of the hydraulic cylinder, it indicates that the piston sealing ring has not failed; If a large oil flow (greater than 30ml / min) is formed, it indicates that the sealing ring of the piston of the hydraulic cylinder is invalid and should be replaced.

④ According to the service time of multi-channel valve, it can be analyzed whether the clearance between valve stem and valve body hole is too large. The normal clearance is 0.01mm, and the limit value during repair is 0.04mm.

⑤ Check the clearance between the valve core of the flow conversion valve and the valve body. The normal value is 0015 ~ 0.025mm, and the maximum clearance shall not exceed 0.04mm. If the clearance is too large or the valve is seriously worn, replace the flow change-over valve. Check the tightness of the contact surface between the check valve and the valve seat in the valve stem. If the sealing is poor, grind the valve seat and replace the valve core. Check the spring. If it is deformed, softened or broken, replace it.

⑥ If the above possible causes are eliminated and the fault still exists, it must be disassembled for inspection. For the CBG gear pump commonly used in ZL50 loader, the end clearance of the pump is mainly checked, followed by the meshing clearance between the two meshing gears and the radial clearance between the gear and the shell. If the clearance is too large, it means that the internal leakage is too large to produce enough pressure oil. At this time, replace the main pump.

The two end faces of the gear of CBG gear pump are sealed by two steel side plates plated with a layer of copper alloy. If the copper alloy on the side plate falls off or is seriously worn, the hydraulic pump will not pump oil with sufficient pressure. At this time, the hydraulic pump should also be replaced.

(2) The bucket retracts weakly or does not act

The possible causes of failure are:

① The main hydraulic pump fails and the oil with sufficient pressure cannot be pumped out;

② The main valve core of the main safety valve is stuck, the sealing of the main valve core is not tight or the pressure regulation is too low;

③ The clearance of the flow conversion valve is too large or the one-way valve in the valve is not tightly sealed

④ The fit clearance between the bucket reversing valve stem of the multi-way valve and the valve body hole is too large;

⑤ The main valve core of the front and rear double acting safety valve is stuck or the seal is not tight;

⑥ The sealing ring of the bucket hydraulic cylinder piston is damaged.

The exclusion methods are:

① Check whether the boom lifting is powerful. If the boom lifting is normal, it means that the hydraulic pump and the main safety valve are free from faults, otherwise the faults shall be eliminated according to the above methods;

② Disassemble the front and rear double acting safety valves, check the tightness and flexibility between the spool valve core and valve seat, one-way valve core and valve body, and clean the valve body and valve core;

③ Check the clearance between the bucket reversing valve stem and the valve body hole to see if it is within the repair limit value (0.04mm). If it is greater than this value, repair or replace it;

④ Disassemble and inspect the bucket hydraulic cylinder (or check whether the seal of the piston of the boom hydraulic cylinder fails first).

(3) Excessive boom hydraulic cylinder drift

Lift the fully loaded bucket, put the multi-way valve in the middle position, and check the sinking distance of the piston rod of the boom hydraulic cylinder, that is, the settlement. After the full load bucket of ZL50 loader rises to the highest position for 30min, the relative displacement of piston rod to cylinder block shall not be greater than 10mm. If the settlement is too large, it will not only directly affect the productivity of the loader, but also affect the operation accuracy of the working device, and sometimes even accidents will occur.

The fault reason may be that the clearance between the valve rod of the multi-way valve boom directional valve and the valve body hole is too large, resulting in internal leakage or sealing failure of the piston of the boom hydraulic cylinder.

The troubleshooting method is: replace the sealing ring of the piston of the boom hydraulic cylinder; Check the clearance between the multi-way valve boom directional valve stem and the valve hole body to ensure that the clearance is within the repair limit (0.04mm); If it is greater than this value, repair or replace it.

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