When repairing a hydraulic pump, identify the cause of the fault from the following three aspects and improve the system.

(1) Check the boom cylinder for internal leakage. The simplest method is to raise the boom and see whether it drops noticeably on its own. If
the drop is obvious, remove the cylinder for inspection, and replace the seal rings if they are worn.

(2) Check the control valve. First clean the relief valve and check whether the valve core is worn; replace it if worn. If there is still no
change after the relief valve is installed, check the wear of the control valve spool; the service limit for its clearance is generally 0.06 mm, and it should be replaced if severely worn.

(3) Measure the pressure of the hydraulic pump. If the pressure is low, adjust it; if the pressure still cannot be raised, the hydraulic pump is
severely worn.

Generally speaking, the main reasons why the boom cannot lift a load are:

A. Severe wear of the hydraulic pump. At low speed, internal leakage in the pump is severe; at high speed, the pump pressure rises slightly, but due to wear and internal leakage, the volumetric efficiency drops significantly and the rated pressure is difficult to reach. Long-term operation of the hydraulic pump further aggravates wear and raises the oil temperature, which causes wear of hydraulic components and aging and damage of seals, loss of sealing capability, and deterioration of the hydraulic oil, ultimately leading to the fault.

B. Unreasonable selection of hydraulic components. The boom cylinder is a 70/40 non-standard series, and its seals are also non-standard parts, resulting in high manufacturing cost and inconvenient seal replacement. The small bore of the boom cylinder inevitably requires a high system setting pressure.

C. Unreasonable hydraulic system design. The control valve and the full hydraulic steering gear are connected in series on a single pump, and the relief valve is set at 16 MPa, while the rated working pressure of the hydraulic pump is also 16 MPa. The hydraulic pump frequently operates at full load or under prolonged overload (high pressure), and the system has hydraulic shocks; contaminated hydraulic oil aggravates pump wear, eventually causing the pump housing to burst (such faults have since been found).

2  Improvements and results

(1) Improve the hydraulic system design. After repeated verification, the advanced priority valve and load-sensing full hydraulic steering gear configuration was finally adopted.

(2) Optimize the design and selection of the boom cylinder and hydraulic pump to reduce the system working pressure.

(3) During use, attention should also be paid to the correct use and maintenance of the loader, regular filtration of the hydraulic oil, maintaining the cleanliness of the hydraulic oil, and strengthening daily inspection and maintenance.