How to adjust the output flow of hydraulic piston pump?

How to adjust the output flow of hydraulic piston pump?

In the hydraulic system of construction machinery, when analyzing the wear and tear faults of hydraulic pumps and their causes, the following three points should be identified during maintenance to find the cause of the fault. The system proposes the following improvement plan:

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

(2) Check the control valve. Firstly, clean the safety valve and check if the valve core is worn. If worn, replace it. If there is still no change after the installation of the safety valve, check the wear of the control valve core again. The clearance limit is generally 0.06mm, and if the wear is severe, it should be replaced.

(3) Measure the pressure of the hydraulic pump. If the pressure is too low, adjust it. If the pressure still cannot be adjusted, it indicates that the hydraulic pump is severely worn.

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

a. The hydraulic pump is severely worn. Severe leakage inside the pump during low-speed operation; During high-speed operation, the pump pressure slightly increases, but due to pump wear and internal leakage, the volumetric efficiency significantly decreases, making it difficult to reach the rated pressure. Long term operation of hydraulic pumps exacerbates wear and tear, leading to an increase in oil temperature and resulting in wear and tear of hydraulic components, aging and damage of seals, loss of sealing ability, deterioration of hydraulic oil, and ultimately causing malfunctions.

b. The selection of hydraulic components is unreasonable. The specifications of the boom cylinder are 70/40 non-standard series, and the seals are also non-standard components, resulting in high manufacturing costs and inconvenient seal replacement. The small diameter of the boom cylinder will inevitably result in high system set pressure.

c. The hydraulic system design is unreasonable. As shown in Figure 1, the control valve and the fully hydraulic steering gear are connected in series as a single pump. The safety valve is set to a pressure of 16 MPa, and the rated working pressure of the hydraulic pump is also 16 MPa. Hydraulic pumps often operate under full load or long-term overload (high pressure) conditions, and there is hydraulic shock in the system. If the oil is not changed for a long time, the hydraulic oil will be contaminated, exacerbating the wear and tear of the hydraulic pump, resulting in the hydraulic pump casing exploding (this type of fault was later discovered).

Improvement and effectiveness

(l) Improve hydraulic system design. After multiple verifications, advanced priority valves and load sensing fully hydraulic steering systems were finally adopted. The new system can allocate flow to the steering system according to the steering requirements, ensuring sufficient oil supply regardless of load size or steering wheel speed. The remaining part can be fully supplied to the working device circuit, thereby eliminating the power loss caused by excessive oil supply in 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 system operating pressure. Through optimization calculations, 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 is set to a pressure of 14MPa, which meets the lifting force and speed requirements of the boom cylinder.

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

The above: Application and advantages of orbital hydraulic motor