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What is the basic method of vibration and vibration reduction transformation of vertical centrifugal pump?

24 May 2022Email

During the operation of the large-scale vertical centrifugal water pump, the vibration is large, the upper and lower bearings are often heated, damaged, and even the connection between the pump shaft and the bearing is worn. The operation of the pump is unstable, which affects the normal water supply and needs to be treated with vibration reduction.

 

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1. The reason for the vibration of the water pump

It 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 3t. Compared with the horizontal pump, it adds an intermediate drive shaft with a length of 3752mm and a diameter of 140mm. Structurally, no modifications have been made other than the addition of a bearing to the intermediate drive shaft. The operating pressure of these four pumps is 0.7-0.85MPa for a long time. Under the conditions of high lift and large flow, such a system with a high center of gravity and a large mass rotates at high speed, and the centrifugal force generated is very large, which will cause a large 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 not enough, resulting in a large displacement of the water pump and each connector. 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 stress conditions of the bearing 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 other sources of vibration such as the motor and drive shaft is also directly transmitted to the pump, forming a superposition of vibrations, further increasing the pump vibration. In addition, this rigid connection increases the external force on the bearing on the pump, which makes the bearing easy to heat up and affects the pump shaft.

 

2. The water pump renovation

For the above reasons, we have taken 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" to the steel pipe at the outlet of the water pump is adopted. Along the water inlet and outlet direction, the flanges at both ends of the connecting steel pipe between the gradually expanding pipe at the 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 stiffness 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 is reduced to 0.35mm after reinforcement.

2. Transform the transmission system. In order to reduce the transmission of the vibration of the motor and the transmission shaft to the water pump, the rigid connection between the water pump and the transmission 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 transmission shaft can be compensated by the elastic coupling, and will not be directly transmitted to the water pump.

3. Results

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

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