Plunger pump wear failure phenomenon and cause analysis
When the wheel loader‘s throttle is increased without a load, the boom lifts slowly, and when the weight is considerable, the boom does not move. The machine’s hydraulic system is a single pump series circuit. We discovered the source of the failure from the following three areas during maintenance and implemented the following system enhancements.
Check the internal leakage of the loader arm cylinder.
The simplest approach to check for this is to raise the loader boom and look for a visible free fall. Dismantle the oil cylinder for inspection if the decline is noticeable. The sealing ring should be replaced if it is worn.
Check whether the loader safety valve and control valve are worn.
Clean the safety valve first, then inspect for wear on the valve core, which should be replaced if it is. Check the wear of the control valve spool again if there is still no difference after the safety valve is installed.
Is there any problem in measuring the pressure of the plunger pump.
If the pressure of the plunger pump is low, adjust it, and the pressure still cannot be increased, indicating that the plunger pump is seriously worn. After inspection, the pressure of the plunger pump is only 5-7MPa, which is lower than the rated pressure of the hydraulic system. After disassembling the plunger pump, it was found that the shaft sleeve was worn, the inner wall of the pump casing in the low-pressure area was severely worn by the gears, and the sidewall was also slightly worn.
The following are the primary reasons why the boom can’t be lifted with a load:
The plunger pump is severely worn.
When the pump is run at low speed, the internal leakage is severe; when the pump is run at high speed, the pump pressure is marginally raised, but the volumetric efficiency of the pump drops dramatically, making it impossible to reach the specified pressure due to wear and internal leakage. Long-term operation of the plunger pump exacerbates wear and raises oil temperature, resulting in wear of the hydraulic components and aging and damage to the seals, loss of sealing ability, deterioration of the hydraulic oil, and, eventually, failure.
The selection of hydraulic components is unreasonable.
The boom cylinder’s parameters are 70/40 non-standard series, and the seals are also non-standard parts, resulting in high manufacturing costs and troublesome seal replacement. Because the boom cylinder bore is tiny, the system’s set pressure is high.
The hydraulic system design is unreasonable.
The control valve and the entire hydraulic steering system are connected in series by a single pump, with the safety valve’s fixed pressure of 16 MPa and the plunger pump’s rated working pressure of 16 MPa. The plunger pump is frequently subjected to full load or long-term overload (high pressure), the system is subjected to hydraulic stress, the oil is not changed for an extended period of time, and the hydraulic oil is contaminated, causing the plunger pump to wear out and burst ( Such failures have been found).
The solution to the serious wear problem of the plunger pump of the wheel loader
- Improve the design of the hydraulic system. Use a load-sensing complete hydraulic steering system with an advanced priority valve. According to the guiding requirements, the new system can prioritize allocating flow to it. It can ensure sufficient oil supply regardless of the size of the load or the speed of the steering wheel, and the residual part can be fully supplied to the working device circuit, minimizing the power loss caused by excessive oil supply to the steering circuit. loss, increase system efficiency, and lower the plunger pump’s working pressure.
- To minimize the system working pressure, optimize the boom cylinder design and replace the plunger pump model. The boom cylinder is standard series 80/4 as a result of optimization calculations. The plunger pump’s displacement is increased from 10 to 14 ml/r, and the system’s set pressure is 14 MPa, which fulfills the boom cylinder’s lifting force and speed requirements.
- Pay attention to the correct use and maintenance of the loader during use, add or replace hydraulic oil regularly, maintain the cleanliness of the hydraulic oil, and strengthen daily inspection and maintenance. With the improved hydraulic system design, the gear pump works more stably and no longer overloads. At the same time, the design of the oil circuit is reasonable, which improves the efficiency of the system, and gives full play to the performance of the whole machine, which improves the work efficiency. The steering action is smooth and reliable, avoiding the phenomenon of unstable steering at high speed.