Cantilever pump vibration problem
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We have a centrifugal pump. The horizontal vibration of the thrust bearing in May was 8.0mm/s. After disassembling it, I found that the bearing was loose, so I took it to be repaired, but the result was not satisfactory, so I ordered the original bearing box. But after replacing the bearing box, I found that the vibration had dropped, but it was still at 5.5mm/s. The shaft is also clocked. The motor vibration is not high. The coupling is no problem either. Spectrum analysis shows that the 6-octave frequency has high amplitude. Can anyone help me analyze the reason?
According to experience: Since this pump has been dismantled and inspected, has the poster noticed that the number of blades in the impeller is 6? It is judged that 6 times the frequency is the liquid sheet passing frequency. It is a high-frequency vibration induced by pressure pulsation in the flow channel of fluid machinery. Solution ideas: 1. Check whether the pump is operating under design conditions. 2. If there is a crossover valve between the inlet and outlet pipelines, you can try to adjust the opening to change the pipeline characteristics and reduce vibration caused by pressure pulsation. 3. Check whether the mesh size of the inlet filter is too small or blocked. 4. Check whether the distance between the impeller blade outlet and the pump body outlet tongue is greater than 6MM. 5. Modify the original impeller, divided into two situations:: When the flow rate is lower than the design condition, grind the concave surface of the impeller blade suction inlet and the convex surface of the impeller blade outlet. When the flow rate is greater than the design operating condition, grind the convex surface of the impeller blade suction inlet and the concave surface of the impeller blade outlet. At the same time, the facing side of the rectifying baffle and the outlet baffle of the pump casing are thinned and chamfered. The above principle is to reduce the tangential velocity component of the fluid in the impeller, avoid vortex or deflow phenomena, and reduce the impact of pressure pulsation on the impeller. 6. Impeller cutting when the working conditions are met can also eliminate the vibration caused by the blade passing frequency.
Check the stress of the inlet and outlet pipelines, and add a support at the cantilever end.
I tried it today and opened the entrance and exit crossing slightly. Vibration down to 5.0
If it turns out to be normal, check to see if the process is running with a smaller flow rate. If the flow rate is low for a long time, you can consider cutting the impeller or replacing it with a new small-diameter impeller.
If the bearing seat has poor rigidity, it will also amplify the vibration. You can consider adding a bracket at the bottom. If there is not one,