Analysis of the Causes of Severe Wear of Excavator Hydraulic Pumps and Improvement Measures

When repairing the hydraulic pump of an excavator, look for the cause of the fault from the following three points and improve the system

(1) Check the internal leakage of the boom cylinder. The simplest way is to raise the boom and see if there is a clear free descent. If the drop is obvious, disassemble the cylinder for inspection. If the sealing ring is worn, it should be replaced.

(2) Check the control valve. First, clean the safety valve and check if the valve core is worn. If it is, replace it. If there is no change after the safety valve is installed, check the wear of the valve core of the control valve. The general clearance usage limit is 0.06MM. If the wear is severe, it should be replaced.

(3) Measure the pressure of the hydraulic pump. If the pressure is too low, adjustments should be made. If the pressure still cannot be increased, it indicates that the hydraulic pump is severely worn.

Generally speaking, the main reasons for the inability of the boom to lift under load are:

A. The hydraulic pump is severely worn. There is severe leakage inside the pump when it operates at low speed. When operating at high speed, the pump pressure slightly increases, but due to the wear and internal leakage of the pump, the volumetric efficiency drops significantly, making it difficult to reach the rated pressure. Long-term operation of the hydraulic pump further accelerates wear, causing the oil temperature to rise. This leads to the wear of hydraulic components and the aging and damage of seals, resulting in the loss of sealing capacity. The hydraulic oil deteriorates, eventually leading to a malfunction.

B. The selection of hydraulic components is unreasonable. The specification of the boom cylinder is a non-standard series of 70/40, and the sealing parts are also non-standard. The manufacturing cost is high and the sealing parts are not easy to replace. A small bore of the boom cylinder will inevitably lead to a high set pressure in the system.

C. The design of the hydraulic system is unreasonable. The control valve and the full hydraulic steering gear are connected in series as a single pump. The set pressure of the safety valve is 16MPA, and the rated working pressure of the hydraulic pump is also 16MPA. Hydraulic pumps often operate under full load or for long periods of overloading (high pressure), and the system is subject to hydraulic shock. If the oil is not changed for a long time, the hydraulic oil will be contaminated, accelerating the wear of the hydraulic pump and causing the pump casing to crack (such faults were later discovered).

2 Improvements and Effects

(1) Improve the design of the hydraulic system. After numerous deliberations, an advanced priority valve and a load-sensing full hydraulic steering gear form were finally adopted. The new system can prioritize the distribution of flow to the steering system according to the steering requirements, ensuring sufficient fuel supply regardless of the load size or the speed of the steering wheel. The remaining part can be fully supplied to the working device circuit for use, thereby eliminating power loss caused by excessive fuel supply to the steering circuit, improving system efficiency, and reducing the working pressure of the hydraulic pump.

(2) Optimize the design of the boom cylinder and hydraulic pump to reduce the working pressure of the system. Through optimized calculation, the boom cylinder adopts the standard series 80/4. The displacement of the hydraulic pump has been 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 usage process, attention should also be paid to the correct operation and maintenance of the loader. Regularly add or replace the hydraulic oil, keep the cleanliness of the hydraulic oil, and strengthen daily inspection and maintenance.