Analysis of the Reason and Shortcoming of Serious Wear of Hydraulic Pump

　　1 Disadvantage appearance and reason analysis

　　There is a shortcoming that the boom lifts slowly when the no-load throttle is large, and does not move when the heavy load is heavy. The hydraulic system of the machine is a single pump series circuit.

　　When repairing, we found the reasons for the shortcomings from the following three points, and made improvements to the system, which are now introduced as follows.

　　(1) Check the internal leakage of the boom cylinder. The simpler method is to raise the boom and see if it has a significant free fall. If the drop is obvious, disassemble the oil cylinder to check. If the sealing ring is worn, it should be replaced.

　　(2) Check the operating valve. First clean the safety valve and check whether the valve core is worn, if worn, it should be replaced. If there is still no change after the safety valve is installed, check the wear condition of the operating valve spool. The use limit of the gap is usually 0.06mm, and it should be replaced if the wear is severe.

　　(3) Measure the pressure of the hydraulic pump. If the pressure is low, stop the adjustment, and the pressure still cannot be adjusted up, indicating that the hydraulic pump is severely worn.

　　After inspection, the pressure of the hydraulic pump is only 5-7MPa, which is significantly lower than the additional pressure of the hydraulic system. After disassembling the hydraulic pump, it was found that the shaft sleeve was worn, the inner wall of the pump casing in the low pressure area was severely "sweeped" by the gear, and the side wall was also slightly worn. It can be seen that the main reasons for the inability of the boom to carry the load are:

　　Analysis of the Reason and Shortcoming of Serious Wear of Hydraulic Pump

　　a. The hydraulic pump is severely worn. When working at low speed, the pump leaks seriously; when working at high speed, the pump pressure increases slightly, but due to the wear and internal leakage of the pump, the volumetric power drops significantly, and it is difficult to reach additional pressure. The long-term operation of the hydraulic pump increases the wear and tear, and the oil temperature rises, which causes the wear of the hydraulic components and the aging and damage of the seals, the loss of the sealing ability, and the deterioration of the hydraulic oil, which eventually leads to the occurrence of defects.

　　b. The selection of hydraulic components is unreasonable. The standard of the boom cylinder is 70/40 non-standard series, and the seals are also non-standard parts. The cost of forming is high and the replacement of seals is inconvenient. The small cylinder diameter of the boom cylinder will inevitably make the system set a high pressure.

　　c. The hydraulic system planning is unreasonable. The operating valve and the full hydraulic steering gear are connected in series with a single pump, the set pressure of the safety valve is 16MPa, and the additional operating pressure of the hydraulic pump is also 16MPa. Hydraulic pumps often work under full load or long-term overload (high pressure) conditions, and the system has hydraulic shocks. If the oil is not changed for a long time, the hydraulic oil is polluted, which increases the wear of the hydraulic pump and causes the hydraulic pump casing to burst (later find such shortcomings).

　　2 Improvements and effects

　　(l) Improve hydraulic system planning. After many proofs, the leading priority valve and load sensing full hydraulic steering gear method were finally selected. The new system can give priority to allocating flow to it according to the steering demand. No matter the size of the load or the unevenness of the steering wheel speed, it can ensure sufficient oil supply, and the remaining part can be fully supplied to the operation equipment circuit, thus eliminating the power caused by excessive oil supply to the steering circuit. Loss, the system efficiency is increased, and the working pressure of the hydraulic pump is reduced.

　　(2) Optimize the shape of the boom cylinder and hydraulic pump to reduce the operating pressure of the system. After optimized calculation, the standard series 80/4 is selected for the boom cylinder. The displacement of the hydraulic pump is increased from 10ml/r to 14ml/r, and the system setting pressure is 14MPa, which meets the lifting force and speed requirements of the boom cylinder.

　　(3) In the process of operation, you should also pay attention to the precise use and maintenance of the loader, increase or exchange hydraulic oil regularly, maintain the cleanliness of the hydraulic oil, and enhance daily inspection and maintenance.

　　After improving the design of the hydraulic system, the gear pump works more smoothly and no longer appears overloaded. At the same time, the oil circuit design is reasonable, the system efficiency is improved, and the operation performance of the whole machine is fully exerted, which improves the working efficiency. The steering action is smooth and reliable, preventing the appearance of "floating" steering at high speeds.

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