Shaft misalignment in the motor of the high-pressure boiler feed water pump
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Phenomenon: Axial shift at the motor end of the high-pressure feed water pump, with the shift amount reaching around 2–3 mm. Tests showed that the vibration, temperature, motor current, and motor power were all normal; there was no obvious shaft shift at the pump end, and the shaft shift at the motor end was absorbed by the diaphragm coupling between the pump and the motor. During startup, the single motor exhibited shaft wobble, but this phenomenon disappeared afterward, and the motor remained in a stable state! Check the position of the motor’s magnetic neutral line – it’s correct! I would like to ask if anyone has encountered similar issues during operation, or if anyone can analyze the reasons for shaft movement `
In the case of large motors with sliding bearings, the rotor automatically finds its center under the balance of electromagnetic forces when the motor starts. However, in motors with rolling bearings, this situation is very dangerous, as the bearings can easily get damaged. It is recommended to have a professional technician check it
After aligning the magnetic flux lines of the motor, measure whether the shaft end distance is appropriate. For reference only
Reply to 1# chen0919: The play of this type of motor is already very large
It might be due to the diaphragm coupling
The magnetic centerline is in the correct position, and the motor is not overheating; therefore, the motor should not be damaged； In most cases, this situation is caused by an offset in the centering position, and re-centering is required ； Additionally, the poster needs to check the coupling diaphragm; over time, it can get damaged as a result of continuous use. . . . For reference only
The poster can test the motor separately to see if there is any deviation between the magnetic center of the motor during operation and the value specified by the manufacturer
All high-pressure feed pumps experience shaft play, and this play is absorbed by the diaphragm coupling between the pump end and the motor. It’s incredible that the motor shaft can shift so much; usually, thrust bearings are used for positioning, and such a large amount of shift would damage the bearings as well.
Thank you for your replies. We have tested the motor individually, realigned the magnetic center line, and also measured the shaft shoulder distance, which is within the values specified by the manufacturer. The motor uses sliding bearings and a diaphragm coupling; indeed, the pump itself has some amount of axial movement, but this amount is very small and essentially cannot be detected by the naked eye. However, we can clearly see that there is at least 2 to 3 mm of axial movement at the motor end. If alignment is poor, the vibration levels at the pump side and the motor side should be high, but no such phenomenon has been observed during operation.