Overheating problem of centrifugal pump motors
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This post was last edited by foam_ZPTK on 2018-8-28 at 14:23. There is a centrifugal water pump in the factory; its motor is experiencing overcurrent and the temperature is 90 degrees. Several motors were tried, but the problem persisted; later, the water pump was disassembled and it was found that the impeller was perforated, so a new rotor assembly was installed. But the new pump shaft is a bit shorter than the old one, so I pulled the coupling on the motor side and the coupling on the pump side out a little. As a result, during operation under load, the vibration levels at the motor and water pump were good at first; however, after one or two hours of operation, the motor’s temperature rose to nearly 90 degrees. The axial vibration of the motor was measured at 11 mm/s while the radial vibration was 8 mm/s. The vibration levels at the water pump were satisfactory. The same issue occurred with two different motors. I’d like to ask what the exact reason is? Is it a motor or a water pump? Is it related to the coupling being pulled out? After replacing the rotor assembly, the motor no longer experiences overcurrent, but the temperature remains above the limit.
It is still necessary to check whether the end-face clearance of the coupling is too small.
When the water pump is operating normally, it is essential to maintain the designed operating pressure; if the pressure is too low, the flow rate will increase, which in turn can lead to an increase in current.
The pressure and flow are normal; the current is also normal now. It’s just that the temperature at the motor end is high. .
Bearings also have a lifespan; replace the motor’s bearings
What is the temperature on the casing? Did you measure it with a handheld thermometer or is it shown on remote monitoring? Take a photo and mark the temperature at those few points!
Measured with a handheld thermometer. The temperature measured is at the bearing on the load side of the motor.
New motors or new shaft bearings will definitely not have problems; the temperature of normal bearings stabilizes after about two hours of operation.
The symptoms are indeed strange; the current in the motor is normal, but the bearing temperature is abnormal. It is recommended to monitor the axial displacement of the motor shaft (however, theoretically, if the motor shaft is pulled forcefully, the thrust bearing of the pump should also heat up, so monitoring this is advised). Also, on the old rotor, the impeller has holes – has anyone checked to find out what caused that? Is it a casting issue or cavitation during the operation?