Water pump noise troubleshooting (part 2)

Operating noise of coupling

For water pumps with elastic couplings, if periodic abnormal noise occurs at the coupling part during operation, accompanied by visible rubber powder falling off, it can be judged as coupling noise, mostly due to the pump shaft and motor shaft poor alignment occurs, and the shaft alignment needs to be re-adjusted after stopping the machine.

Most of the water pump operation problems will be manifested as abnormal noise. According to the noise characteristics, accurately and effectively find the cause of the problem, and the water pump can be overhauled faster and save time.

In some systems, the pump does not have enough power. It can be observed through flow meters, pressure gauges, ammeters and other components that the pump cannot achieve the design parameters in actual operation. This situation usually occurs as follows:

 

  1. Reverse rotation

This problem only occurs on three-phase motors, and there is no possibility of reverse rotation for single-phase motors. User can check the rotation of the motor fan blades according to the pump identification. If the reverse is true, user can adjust the phase sequence of any two phases of the motor power line. It should be noted here that the motor with an inverter can only adjust the line sequence between the inverter and the motor. The power line sequence of the inverter will not affect the motor's direction of rotation.

 

  1. Water pump cavitation

The cavitation of the water pump will cause the performance curve to decay, the operating point will be shifted, and the flow head will not reach the preset value. However, cavitation problems are more likely to be discovered by noise abnormalities, so the cause of the problem and the treatment method have been explained above.

 

  1. There is air in the pump body

There is air in the pump body that has not been exhausted. After being compressed, the remaining gas stays at the top of the pump body at high pressure, which affects the flow path and loses the performance of the pump. This problem can be checked by opening the exhaust valve of the pump body and observing whether there is any gas discharged. After exhausting the gas completely, turn on the water pump and the fault disappears.

 

  1. Incorrect opening of water pump valve

If the valve opening of the inlet and outlet of the water pump is not suitable, or the inlet filter is seriously blocked, the operating point of the water pump will be shifted. To judge this abnormality, it is necessary to rely on the flow meter and pressure gauge installed in the correct position on the system. The condition point is compared with the pump curve and the design operating point, and the valve opening is adjusted to make the double operating point coincide.

If the system is not equipped with a flow meter, a pressure gauge, or the installation table position is wrong, the motor current needs to be used to estimate the operating conditions of the pump. The motor current can be measured by the ammeter in the control cabinet or with a pinch meter. Calculate the shaft power based on the motor efficiency and power factor, compare the shaft power curve in the water pump curve chart, and determine the operating point as the basis for adjusting the valve.

 

  1. Insufficient water pump operation frequency

Regardless of whether it is an automatic control method with sensor access or manual speed regulation, if the pump is controlled by the inverter, if the setting is improper, the running speed of the pump is too low, it may not meet the system requirements, and the inverter needs to be checked at this time.User can increase frequency properly. Through the above-mentioned instrument observation or current-shaft power estimation and evaluation to determine the pump operating status.

 

If none of the above points can solve the problem of insufficient pump output, then the cause of the problem may be inside the pump body. For example, impeller size is incorrect, impeller cavitation damage is serious, mouth ring wear is serious, etc., the pump needs to be checked by a professional.

 

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