How to repair a qualified hydraulic pump？

In the field of construction machinery, repairing hydraulic pumps is a commonplace. How to repair a qualified hydraulic pump? On this issue, many technicians and experts have published many papers and exchanged many experiences. I have also benefited a lot from it.

In recent years, the control variable system of high-quality hydraulic pumps has undergone great changes, and the control forms are also different, all of which increase the complexity of pump maintenance. Some pump failures are not a problem that can be solved by changing the cylinder block, oil distribution plate, and plunger. To repair a hydraulic pump, not only the pressure and flow must meet the maintenance standards, but also the variable adjustment mechanism of the pump must meet the performance requirements and have a longer service life.

The working principle of the pump is just one sentence, "the volume change in a closed container". Therefore, the problem to be solved by repairing the pump is the two keywords of airtightness and variation. The amount of change refers to the oil pumping process of the pump, that is, the process of sucking oil from small to large, and the process of draining oil from large to small. Because we are using variable pumps now, we extend the meaning of this variable to the current servo variable system. Because this system controls the change of the pump, the essence of repairing the pump is to repair its airtightness and its change.

Airtightness means airtightness. For some hydraulic pumps, the airtight container is the cylinder body, but it is not an isolated piece. It is composed of a cylinder body, plunger, oil distribution plate, thrust plate, and intermediate to form a closed container. container. Therefore, it is necessary to check whether the container is airtight, check these parts, the joint surface of the cylinder body and the oil distribution plate, which is a spherical sealing surface.

The joint surface of the oil distribution plate and the intermediate body is a flat seal. The clearance between the plunger and the cylinder bore is a clearance seal. The joint surface of the shoe and the thrust plate is a flat seal. Only these parts meet the technical requirements of sealing to ensure the tightness of the cylinder.

Let's talk about the hydraulic pump variation, variable plunger pumps are equipped with maximum swing angle and minimum swing angle limit screws. The general swash plate swing angle is between 2-25. The larger the swing angle, the greater the plunger stroke and the greater the pump flow. The smaller the swing angle, the smaller the plunger stroke, and the smaller the pump flow. The change of the pump is controlled by the servo plunger of the pump and various adjustment systems. At present, the variation of the pump on the excavator is controlled by three aspects. Namely: (1) Power shift solenoid valve control (2) Total power variable spool control (3) Pump swash plate control pressure control.

Therefore, to repair a pump, it is necessary to repair the airtight performance of the pump, but also to repair the change problem. Simply replace the accessories in the pump, such as the cylinder, the oil distribution plate, the plunger, and the nine-hole disk. It can solve the airtightness of the pump. If the variable mechanism of the pump is ok, the pump can be repaired by replacing these parts. If there is a problem with the variable mechanism, simply replacing these parts will not completely solve the problem. The amount of change of the pump determines the stroke of the plunger, which determines the flow rate of the pump, and also determines the performance of the hydraulic pump to automatically adjust the power.

In maintenance and remanufacturing, attention is paid to the coordination of machining accuracy and friction materials. If the direct grinding method is used, it is not feasible to grind the cylinder and the disc.

The service life of a hydraulic pump depends on the wear resistance between the friction bodies under general conditions. From the theory of tribology: we know that between the friction bodies, a material is relatively soft, such as copper. When the hardness of another mating material is high, the friction body is wear-resistant. Some hydraulic pump cylinders are made of medium-carbon alloy steel, and their hardening treatments are all gas nitriding. The surface hardness of the cylinder is high, but the surface hardening layer is very thin, generally between 10-30 wires.

In maintenance, the worn surface is ground. If the grinding amount is large, the hard layer surface will be worn away. The friction surface has no hardness and will wear again soon. For the parts with insufficient surface hardness, we have done the surface wear-resistant hardening treatment before use, thereby increasing the service life of the mating body. In terms of friction body material coordination and surface hardness and wear-resistant treatment, we have done some practice and have received good results.