1. Find the cause of the fault from the following three points during the maintenance of the excavator and improve the system:
(1) Check the inner leakage of the boom cylinder. The easiest way is to raise the boom to see if it has a clear free fall. If the drop is obvious, disassemble the cylinder and check. If the seal ring is worn, it should be replaced.
(2) Check the control valve. First clean the safety valve, check whether the valve core is worn, and replace it if worn.
If there is no change after the safety valve is installed, then check the wear of the spool of the control valve. The clearance limit is generally 0.06mm, and it should be replaced if the wear is serious.
(3) Measure the pressure of the hydraulic pump. If the pressure is low, adjust it, but the pressure can not be adjusted, it means that the hydraulic pump is seriously worn.
Generally speaking, the main reasons why the boom loading cannot be improved are:
A. The hydraulic pump is badly worn. During low-speed operation, the internal leakage of the pump is serious; during high-speed operation, the pump pressure is slightly increased, but due to the wear and internal leakage of the pump, the volumetric efficiency drops significantly and it is difficult to reach the rated pressure.
Hydraulic pumps work for a long time and aggravate the wear, the oil temperature rises, which causes the wear of hydraulic components and the aging and damage of seals, the loss of sealing ability, the deterioration of hydraulic oil, and finally the failure.
B. Unreasonable selection of hydraulic components. The specifications of the boom cylinder are 70/40 non-standard series, and the seals are also non-standard parts. The manufacturing cost is high and the seals are inconvenient to replace. The small diameter of the boom cylinder will inevitably make the system set pressure high.
C. The hydraulic system design is unreasonable. The control valve and the full hydraulic steering gear are connected in series by a single pump, the safety valve setting pressure is 16MPa, and the rated working 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 shock, no oil change for a long time, the hydraulic oil is contaminated, and the hydraulic pump wear is exacerbated, so that the pump casing of the hydraulic pump burst (later found Such failures).
2. Improvement and effect
(1) Improve the hydraulic system design. After many demonstrations, the advanced priority valve and load sensing full hydraulic steering gear were adopted in the end. The new system can give priority to the flow distribution according to the steering requirements. No matter the load size or the steering wheel speed, it can ensure sufficient oil supply, and the remaining part can be fully supplied to the working device circuit, thereby eliminating the power caused by the excessive oil supply to the steering circuit. Loss improves the efficiency of the system and reduces the working pressure of the hydraulic pump.
(2) Optimize the design of boom cylinder and hydraulic pump to reduce the working pressure of the system. Through optimization calculation, the boom cylinder adopts the standard series 80/4. 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) During the use process, attention should also be paid to the correct use and maintenance of the loader, adding or replacing hydraulic oil regularly, maintaining the cleanliness of the hydraulic oil, and strengthening daily inspection and maintenance.
