Created on:2021-05-07 08:47

Failure and troubleshooting of radial variable piston pump system unable to reach normal working pressure

Failure and troubleshooting of radial variable piston pump system unable to reach normal working pressure

① Function, structure and fault phenomenon the hydraulic system used in a building material factory uses radial variable piston pump (Bosch Company, Germany) as oil source. Figure 7-32 shows the structural principle of the pump. The star shaped rotor 3 of the hydraulic cylinder is installed on the distribution shaft 4. The driving torque generated by the rotor 3 is transmitted through the cross coupling 2, and the stator 7 is not subject to other transverse forces. The radial plunger 5 located in the rotor 3 clings to the eccentric stator 7 through the statically balanced slipper 6. The plunger 5 is connected with the slipper ball and is locked by a snap ring. Two retaining rings 8 clamp the slippers on the stroke stator. When the pump rotates, it presses on the stator 7 by centrifugal force and hydraulic force. When the rotor 3 rotates, due to the eccentricity of the stroke stator 7, the plunger 5 moves back and forth, and its stroke is twice of the eccentricity of the stator. Changing the eccentricity can change the displacement of the pump. From the structure of the pump, it can be seen that the slipper and the stator are in line contact, and the contact stress is high. When the valve distribution shaft is subjected to the radial unbalanced hydraulic pressure, it is easy to wear, and the worn clearance can not be compensated, which increases the leakage. Therefore, the working pressure, volumetric efficiency and speed of the pump are lower than those of the axial piston pump.

During the use of the pump, the hydraulic system can not reach the normal working pressure (the working pressure is required to be higher than 25 MPa, and the pressure can be adjusted to gradually reduce, and the flow requirement can be adjusted automatically), resulting in the failure to lift the mold and meet the use requirements.

② According to the structural characteristics of radial piston pump, the reason is that the contact between slipper and stator is line contact, which is easy to cause wear. Through the disassembly and inspection, it was found that the fitting arc surface of the slipper and stator was seriously worn, the alloy layer on the arc surface had wear marks, and part of the alloy layer had been worn off. The wear degree of stator inner surface is slight, only scratch. Because the arc thrust surface of the slipper is larger than that of the piston, it can not be tightly attached to the inner surface of the stator, so the internal leakage increases due to the loose sealing, which makes the hydraulic system unable to establish a higher pressure.

③ According to the above analysis, the arc surface of the slipper and the inner surface of the stator are repaired.

a. Repair of slipper: there is an alloy layer on the arc thrust surface of slipper, and now there are wear scars. In view of this situation, the grinding method is adopted. The inner arc surface of stator is used, the plane tooling is used to lean on the grinding track, and 800 grinding paste is added. After grinding, the circular arc thrust surface of the slipper is close to the inner surface of the stator. In order to check the fit of the two sides after grinding, kerosene is poured into the sliding shoe through the hole, and kerosene does not leak, which proves that the grinding effect is good and plays a sealing role.

b. The wear degree of the inner surface of the stator is slightly light (only scratch). Metallographic sandpaper is used to remove the scratch on the surface, and the arc thrust surface of 8 slippers is matched with it. The circular arc thrust surface of the slipper does not leak oil.

After the parts are repaired, the assembly is carried out, and the pump is connected to the actual hydraulic system, which runs well, can establish a high pressure (up to 35 MPa, working pressure up to 28 MPa), the mold can be easily lifted, and then the pressure gradually decreases, the flow rate increases to more than 80 l / min, the efficiency is improved, which fully meets the work requirements.

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