Gear pump fault diagnosis and maintenance analysis (1)

In mechanical engineering equipment, hydraulic transmission is used more frequently. As the “heart” of the hydraulic system, the hydraulic pump is usually in a harsh environment. Therefore, troubleshooting the maintenance of the hydraulic pump is the key to ensuring the normal operation of the hydraulic system.

The hydraulic pump is simple in process and easy to process. Therefore, it is used more in mining machinery, metallurgical machinery, machine tool equipment, and construction machinery.

When the gear rotates in the direction shown, the lower oil chamber is separated by the gear, the volume is increased from small, a partial vacuum is formed, and the oil is sucked under the action of atmospheric pressure, and the upper gear is gradually meshed, so that the working space volume is changed from large to small. The squeezed oil enters the oil pipe output. The suction and discharge are separated by the meshing lines of the two gears.

The amount of resistance at the exit of the gear pump determines the pressure at the discharge port. If the leakage and other factors are not considered, the amount of suction flow should be the same as the output flow. However, in fact, both sides of the pump and the gear need to be lubricated, and the pump body can never be fitted without a gap. There is little fluid loss in the pump, so the discharged liquid is always less than the inhaled liquid, that is, it cannot reach 100. % operating efficiency, as a gear pump product, a small amount of fluid loss is inevitable. A well-run pump can achieve efficiencies of 95% to 98%.

Generally speaking, the leakage of the gear pump, the trapped oil and the imbalance of the radial hydraulic pressure affect the performance index and life of the gear pump. When the gear pump fails, it will affect the entire hydraulic system, and then the performance index of the system will not meet the requirements. Requirements. In practice, the volumetric efficiency of the gear pump is lower than 5% of the factory-qualified index; the surface of the friction pair such as the gear end face is drawn, stuck, or ablated; the parts are broken and damaged; The fault.

Troubleshooting
As far as the current technical level and means are concerned, the following methods are mainly used to diagnose the failure of the hydraulic gear pump.

Functional diagnosis
Diagnose according to the functional parameters (pressure, flow, volumetric efficiency) of the hydraulic equipment, or use the changes in the operating parameters (speed, displacement, etc.) of the hydraulic equipment. In general, when a hydraulic device fails, its operating parameters change. When the hydraulic system hydraulic pressure is lower than a certain rated value or there is a sharp fluctuation, it means that the oil passage has a malfunction such as blockage or internal leakage.

Vibration diagnosis
This method is more common and mature. The vibration process occurring in the hydraulic system contains a wealth of information that fully reflects the technical status of the hydraulic components and the entire equipment.

In the failure of the hydraulic gear pump, one of the common types of failure is the bearing failure. However, compared with the natural vibration amplitude of the hydraulic pump, the additional vibration generated by the bearing failure is relatively weak, so the fault information is not taken out from the signal. It's easy. At present, the effective diagnosis method of hydraulic pump bearing fault is still lacking. The actual diagnosis shows that it is more reliable to diagnose bearing faults by using frequency domain diagnostic method.

When the bearing inside the pump is faulty, it will cause additional vibration of the system. This vibration signal contains a wealth of information and is well suited for fault diagnosis using the frequency domain method. According to the tribology theory, the smoothness of the raceway is damaged whether there is damage on the inner ring, the outer ring raceway or the roller. As soon as the roller rolls over the damage, a vibration will occur.