# Investigation of Failure Causes of Oil Pump Based on Operating Conditions
## 5 Failure Tests  
### Motor Bearing  
During the motor operation, the bearing is located at the end of the motor and maintains a smooth rotation. The bearing, combined with the motor, is exposed to high stress levels during the motor operation. Therefore, the proper lubricating conditions must be maintained, and the penetration of external pollutants must be prevented. When the motor has been operating for a long time, friction may occur between bearing components owing to poor lubrication or aging of the lubrication. In addition, the penetration of foreign substances and piling up on the inside of the bearing results in the adhesion of the bearing. In this case, subsequent failures such as vibration and noise due to bearing rotation and faults in operating the equipment may occur. In the present study, the bearing sample was subjected to lubrication failure and foreign substance injection failure to collect data for a quantitative database. Figure 3a shows the results of the vibration data in the normal and abnormal states. In the case of Figure 3b, the vibration occurred in each frequency band, similar to a normal database. In addition, the amplitude has been decreased in all areas of the motor in the radial direction. However, over 400 Hz, it can be confirmed that the vibration was slightly increased. Figure 3c shows the vibration data according to the contamination state inside the motor bearing. Overall, it was confirmed that vibration occurs in the frequency band similar to the normal condition. However, it was confirmed that the amplitude near 400-450 Hz in the radial direction increased significantly owing to the high-speed rotation. Based on Figure 3, it was confirmed that the severity of the vibration of the motor bearing was more dependent on the state of contamination inside the motor bearing rather than the absence of lubrication. This is thought to be due to an immediate reaction when pollutants are generated. However, once the motor is operated over a longer time period, it is expected that more severe problems will occur, such as heat generation, wear, and adhesion of the bearing.  
\begin{table}
\begin{tabular}{c c} \hline
**Manufacturer** & **KRAL Pump** \\ \hline Pressure & 0 to 0.1 bar (inlet) \\  & 0 to 1.3 bar (outlet) \\ Temperature & 25–35 \({}^{\circ}\)C (inlet) \\  & 28–38 \({}^{\circ}\)C (outlet) \\   Flow rate & 95–99.99 L/min (inlet) \\  & 95–99.99 L/min (outlet) \\ Rotational speed & 1770 (RFM) (Motor, pump) \\ \hline \end{tabular}
\end{table}
Table 5: Manufacturer and operating conditions of the test bed for the pump.  
Figure 4 shows examples of wear, scratches, and dents that appear on the bearing by comparing the conditions prior to testing and the tested conditions. After the test, several scratches and dents were found in several places on the motor bearing. In particular, the wear, scratches, and dents appeared on the outer surface of the inner ring and on the inner surface of the outer ring after the test.  
Figure 3: FFT for (**a**) normal state and abnormal states such as (**b**) without lubrication and (**c**) contamination of the motor bearing.