Water Pump Noise Troubleshooting (Part 1)

Most of the electromechanical products will produce noise during operation, this is a normal, but the noise also has a reasonable range. In the final analysis, any noise outside the range will have two reasons.

One is that the equipment is not qualified and the noise exceeds the standard. Another one is that the equipment is not operating normally. Water pumps are no exception. This article introduces the troubleshooting and treatment methods of abnormal noise during water pump operation.

The main reasons of pump noise are as follows

Pump head noise

During the operation of the pump head, the sound of water friction between the impeller and the pump casing is normal noise, and this noise will increase as the pump flow rate and head parameter becomes larger. But there may be abnormal noise in the pump head:

  • Causes of friction : If the pump head has a sharp metal friction sound when the pump is running normally, after the pump is powered off, remove the motor fan cover and manually crank, and there will be a certain angle resistance increase, accompanied by friction noise, the other angle resistance is normal, and there is no noise. It can be judged that there is hard friction in the pump body, and there are usually two reasons for friction:

  1. Foreign matter may enter the pipeline from welding slag or iron filings from the suction port of the water pump during operation, or it may be caused by the transfer of nuts and gaskets from the outlet of the water pump during the construction process. The treatment method needs to open the water pump to remove foreign objects.

  2. The impeller of the water pump is poorly installed. This situation is mostly due to the first time the pump is started or the pump head is disassembled and maintained, and the pump head needs to be reinstalled and positioned after opening the pump head.

Regardless of the two types of failures, the parts need to be replaced depending on the wear and tear.

  • Causes of cavitation : If the pump head has a crackling sound when the pump is running normally, try to adjust the pump outlet valve when the pump inlet valve is fully opened. If the valve is opened, the sound becomes louder, and if the valve is closed, the sound becomes smaller. When the abnormal noise disappears after reaching a certain angle or fully closed, it can be judged as water pump cavitation.

There are many reasons for cavitation:

  1. System design problems. It mostly occurs when the pump is first started and debugged. It’s mainly related to the inlet water temperature and inlet pressure. Lowering the water temperature or increasing the inlet pressure of the pump can solve this abnormality, or replace the water pump with low cavitation margin. Then this problem can be solved.

  2. The inlet filter of the water pump is clogged. It is more common for long-term normal operation. If the water pump valve has not been adjusted, this abnormality is suddenly found. It should be because the system has been running for a long time. The inlet filter of the water pump accumulates impurities and causes blockage. Open and clean the filter will resolve this.

  3. When the operating flow is too large, the NPSH of the pump will increase with the increasing of the flow rate. If the pump is operated at the design operating point, the NPSH is still sufficient. When the operating point moves to the right, the NPSH will increase, the system cannot meet the requirements, and cavitation will occur. Various instruments can be used to determine the pump operating point, close the pump outlet valve, and restore to the design operating point.

 

Motor noise

Motor running noise is usually the airflow noise of the motor's cooling fan, which is much larger than the friction noise of the motor rotor bearing.

However, abnormal noise may also appear in the motor part:

  1. There may be friction between the cooling fan and the fan cover. If the noise disappears after removing the fan cover, it is judged to be abnormal. Check and adjust the fan blade or fan cover to solve the abnormality.

  2. Motor rotor bearing is faulty. If the fan cover is removed and the motor is cranked alone, and the full-angle resistance is abnormal, it can be judged as a bearing fault. There are two possibilities. One is that the bearing is rusted due to water ingress, and the other is that the motor heats up abnormally and the bearing is greased. The motor bearing needs to be replaced to solve this abnormal noise.

The frequency converter and the electric power are not compatible with the noise.

This noise is manifested by the sharp whistling of the main part of the motor, and the inverter must participate in the power circuit. The cause of the noise is that the carrier frequency (switching frequency) of the inverter is incompatible with the motor, and it is not a quality problem of the motor or the inverter.

If the circuit is adjusted on site, or the inverter is replaced, or it is changed to direct start/star-angle connection start, the noise disappears. It can be judged as such noise.

Users can try to refer to the inverter manual and adjust the carrier frequency (switching frequency) in the inverter settings. After the adjustment, the noise can be reduced or eliminated.

 

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