Slow fault diagnosis of mobile arm lifting of ZL40 loader

When a ZL40 loader is in use, it is found that the boom cylinder and bucket cylinder work slowly, the lifting capacity is weak, and the lifting time is more than 15s. (the standard time for lifting the boom cylinder should be 7S). In this case, should be based on hydraulic system diagram itemized analysis, investigation.

At first, it was considered that the hydraulic pump was out of order. After the replacement of the new pump, the fault still remained. So check the inside of the boom just leaking. When detecting the hydraulic distribution valve, it is found that the hydraulic oil in the valve is leaking seriously and the working pressure is very low. Inspection found that the safety valve has a O - shaped sealing ring fracture, resulting in hydraulic oil leakage. Although troubleshooting, but downtime for up to January years, waste of materials, increased costs, affecting the work.

Therefore, the investigation of such failures, we must use the hydraulic system schematic diagram of the boom cylinder lift system in accordance with the following order of itemized investigation:

First check the amount of hydraulic oil; if the amount of oil is insufficient, the gear pump can not normally suck the hydraulic oil, resulting in oil supply intermittent, unstable pressure, will lift the arm lift. Check the hydraulic oil strainer again; if the strainer is blocked, the oil supply will be reduced, the pressure will be lowered, and the lifting of the boom will be weak.

Then check the gear pump: start the engine, loosen the gear pump oil outlet joint and observe the output of oil, if the oil pump or pump oil consumption, shows that the gear pump failure; gear pump gear wear sleeve, gear backlash, front and back surface side wear, and seal and seal damage so, all the gear pump will not pump oil or oil pump pressure is low, resulting in the lifting cylinder to lift, lift slowly.

Then check the automatic settlement arm cylinder; the bucket weights of the boom cylinder rises to the limit position, the handle in neutral position (or the engine stops running, keep 15min) observed after automatic subsidence boom; ZL40 load sinkage machine should be less than 10min. It has been detected that the amount of subsidence has not exceeded the specified value, indicating that the inside of the boom cylinder is not leaking and work well.

Finally, check the distribution valve: the distribution valve consists of moving arm rotating bucket valve, overflow slide valve, oil supply valve and a safety valve, safety valve spring fracture, if the distribution of the valve spool is too soft, damage and closed lax, will cause the pressure is too low, the arm cylinder lift slowly, unable to lift. In the rotating bucket cylinder front cavity and a back cavity of the oil has the overflow oil supply valve, when the hydraulic oil is not clean or debris into the spool and the valve seat, the valve will cause poor sealing; if the valve spool and the sliding seat contact surface is damaged, or spring break, too soft, will reducing the pressure (pressure standard rotating bucket overflow front chamber of the cylinder oil supply valve for 7MPa working pressure standard cavity fill oil valve overflow is 13MPa), so that the rotating bucket cylinder failure. Method for detecting pressure valve distribution, distribution valve test plug removed, mounted on a test pressure gauge; start the engine and speed control in 1800r/min (rated speed); the boom cylinder handle, the boom cylinder up to the limit position, and observe the pressure gauge reading. Standard work pressure of 14 MPa, not up to this standard work pressure, that is, the internal hydraulic oil leakage, the lower the pressure, indicating that the more serious leakage, safety valve must be adjusted or disassembled repair.

ZL40 loader repair valve before the allocation of pressure 9MPa, and the standard pressure, at this time the boom cylinder speed is also within the specified 7S, indicating that the fault has been excluded.