Pump body vibration
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Dear poster, the two D48-50*12 horizontal multi-stage centrifugal pumps in my factory operate normally in terms of vibration once they are started up; the vibration level is around 2.0 mm/s. Over time, after about half an hour, the vibration at the drive end of one pump remained unchanged, while the vibration at its rear end increased to around 4.5 mm/s. In the case of the other pump, the vibration levels on both the front and rear sides started to rise, eventually stabilizing at around 5 mm/s. The vibration level of the motor remained stable at around 2.0 mm/s. The temperature of the fluid is between 50-60 degrees, and the outlet pressure is 5.5 MPA. The motor’s vibration level remains stable at around 2.0 mm/s. All rotors have been dynamically balanced as a whole.
Possible reasons for increased vibration in horizontal multi-stage centrifugal pumps include: 1. **Bearing problems**: Worn bearings or insufficient lubricant can lead to increased vibration. 2. **Imbalance in axial or radial forces**: Uneven distribution of axial or radial forces resulting from long-term operation. 3. **Pump and motor alignment issue**: Inaccurate alignment may occur, causing vibration to increase over time as the machine runs. 4. **Impeller wear or blockage**: After long-term operation, the impeller may wear out or become blocked by debris, affecting the hydrodynamic balance. 5. **Medium temperature changes**: Changes in the medium’s temperature can affect the fluid properties inside the pump as well as the thermal expansion and contraction of its components, thereby leading to increased vibration. It is recommended to carry out the following inspections and maintenance: - Inspect and clean the impeller to ensure there are no impurities blocking it. - Check the alignment of the pump and motor, and make any necessary adjustments. - Inspect the bearings and replace the lubricant, or replace the bearings that are severely worn. - Monitor the temperature stability of the medium and assess its impact on pump performance. These measures help reduce vibration and ensure the proper operation of the pump. .
It is also possible that the pipeline has an effect on the pump, causing vibration in the pump body. You can check whether the pipeline is vibrating.
There are many reasons that can affect the vibration of multi-stage pumps, and dynamic balancing is just one of the checks that need to be performed. It isn’t specified whether it’s a bearing or a bearing sleeve, nor whether it’s a horizontal disk or an equilibrium drum. What is the fit clearance between the bearing and the shaft? What is the clearance fit with the bearing? It’s for the bearing bush; what is the clamping force on the back of the bush? What is the gap width? What about the optical axis runout value? What is the total number of strings? How much has been allocated for splitting the strings? I once encountered a boiler feed pump with a 9-stage impeller; after replacing the bearings, the vibration level remained at 6-7. During the major overhaul, all the measurements were taken again, and it was found that the shaft runout was 0.07, which means the shaft was slightly bent. No wonder the vibration level remained high even after replacing the bearings.