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Improvement of Vibration and Damping of Vertical Centrifugal Pump

19 Nov 2020Email

Improvement of Vibration and Damping of Vertical Centrifugal Pump

 

 

During the operation of the large vertical centrifugal water pump, there is a large vibration, the upper and lower bearings are often heated and damaged, and even the connecting parts of the pump shaft and the bearing are worn. The operation of the water pump is unstable, which affects the normal water supply and needs to be damped.

 

  
A.  Analysis of the causes of pump vibration   

1. The domestic vertical water pump 28SLA-10 is directly transformed from a horizontal pump. The vertical height between the motor base and the water pump base is 4.3m, and the drive shaft system weighs up to 3t. Compared with the horizontal pump, it adds an intermediate drive shaft with a length of 3752mm and a diameter of 140mm. In terms of structure, apart from installing a bearing on the intermediate drive shaft, no modification has been made. The operating pressure of these four water pumps is 0.7~0.85MPa for a long time. Under the working condition of high lift and large flow, such a system with high center of gravity and high mass rotates at high speed, and the centrifugal force generated is very large, which will cause larger vibration of the unit. In addition, the rigidity of the connection between the bracket and the water pump in the water inlet and outlet directions is insufficient, resulting in a large displacement of the water pump and the connecting parts. The displacement of the water pump during operation causes the stress condition of the upper bearing to change, and the vibration increases, so it is easy to generate heat. If the displacement of the pump is corrected and the bearing conditions are improved, the vibration intensity of the system can be reduced.  
2. There is a rigid connection between the water pump and the drive shaft. Due to manufacturing and installation reasons, the pump shaft is concentric with the drive shaft during operation, causing the pump to vibrate; the vibration generated by the motor, drive shaft and other sources is also directly transmitted to the pump, forming a superposition of vibrations, and further increasing the pump vibration. In addition, this kind of rigid connection increases the external force that the bearing on the water pump bears, causing the bearing to easily generate heat and affect the pump shaft.  

 

 

B. Renovation of water pump   
For the above reasons, we took the following two steps to transform.  
1. Strengthen the rigidity of the pipeline. Considering that it is difficult to reinforce the water pump, the method of welding "reinforcing ribs" at the outlet of the water pump is adopted. Along the water inlet and outlet directions, the flanges at both ends of the connecting steel pipe between the diverging pipe of the water pump outlet and the water outlet valve are welded with 8 steel plates with a thickness of 32mm and a width of 100mm. Increase the rigidity of the steel pipe, reduce the amount of deformation, and resist the displacement of the water pump. After measurement, the displacement of point A of the water pump drops to 0.35mm after reinforcement.  
2. Transform the transmission system. In order to reduce the transmission of vibration of the motor and drive shaft to the water pump, the rigid connection between the water pump and the drive shaft is changed to an elastic connection. Using GB4323-84 elastic sleeve pin coupling, the maximum compensation displacement of the centrifugal pump is 0.6mm, and the compensation angle is 1°30°. In this way, the vibration of the motor and the transmission shaft can be compensated by the elastic coupling and will not be directly transmitted to the water pump.  

3. Results of transformation   
After the transformation, the vibration of the pump was reduced from 4.3cm/s before the transformation to 1.48cm/s. According to the vibration intensity standard ISO2372-1974, it can be determined that the pump operation is in the excellent zone. At the same time, the pump runs smoothly, the upper bearing only needs to be maintained normally, and the pump shaft is not worn out, indicating that the transformation is successful.

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