Centrifugal pump failure, resonance issue – please help analyze it. Thank you
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It is a DL vertical multi-stage centrifugal pump with a flow rate of 260 and a head of 70. The unit operates in a one-main-pump-plus-one-backup-pump configuration. After three months of stable operation, resonance occurred in the main pump; whenever the main pump was running, vibrations appeared in the entire piping system of the unit as well as in the backup pump. During the first maintenance check, the technician closed the outlet valve of the main pump, and no resonance was detected while the pump was running. When the outlet valve was slowly opened again, the resonance in the main pump increased. The technician concluded that the outlet valve was the cause of the vibrations and considered replacing it. I would appreciate it if experts could help determine whether this conclusion is valid, as replacing the outlet valve is a rather complicated and difficult process. Thank you for your assistance.
The pump should be fine. Has the inlet pipeline been checked? Could it be that the filter is clogged or that some other issue is causing a vacuum condition?
Agree with what was said above; checking the inlet pipes might also reveal any foreign objects that have gotten in
At first, there were no problems, but then issues arose, which indicates that the original operating conditions and environment have changed. In addition to what was mentioned above, the conditions that cause cavitation should also be checked. Also, check whether the bolts of the pipelines and pumps are loose. Measure the bearing temperature of the motor to determine if its bearings are in good condition. Furthermore, examine the vibration levels of both the motor and the pump body to identify the underlying causes.
Agree with the second-floor opinion; it’s likely there’s a blockage in the inlet pipeline. Or the pressure of the upstream suction device has decreased significantly compared to before.
This post was last edited by Shutong on 2020-7-9 at 11:37. The outlet flow channel is completely broken, with fragments getting stuck in the impeller; the pipeline is not unobstructed, for example, there may be air bubbles at the outlet; the outlet valve’s plate has fallen off or it isn’t open; air is entering at the inlet, resulting in an uneven flow field and pressure fluctuations. These reasons all lead to vibration in the pumps and pipelines, directly or indirectly. But it cannot produce resonance. If the internal stresses resulting from thermal expansion and other factors in the pump body cannot be relieved, it will cause changes in the stiffness of the shaft support system. Resonance occurs when the resulting stiffness is an integer multiple of the system’s angular frequency. It has little to do with valves
It is recommended to first check the opening degree of the outlet valve to see if the valve core has fallen out
Several reasons for the vibration: 1. The base frame is not securely fixed, with loose fasteners； 2. The pump’s suction condition is poor, with cavitation occurring ； 3. Poor balance of the rotor system, resulting in vibration ； 4. Has the critical speed been calculated? It is prone to resonance with other connected equipment ； Please check each item in the order mentioned above. Since both the traffic volume and the vibration levels change, it is likely the fourth cause: replacing or altering the auxiliary equipment. Netizens have said that replacing the valve is also a solution; it is recommended to use a valve of a different type from the original one (swap it with another valve) to rule out resonance caused by high-frequency vibration of the valve ； If that doesn’t work, try changing the stiffness of the pump support to adjust its natural frequency and avoid resonance, or add flexible connections/metal expansion joints between the pump and the main unit to isolate vibrations.
The inlet pipelines for the main pump and the backup pump are each 1.5 meters long, with an inlet valve installed on each of them. Both the inlet pipelines of the main pump and the backup pump are connected to the main pipeline. The problem is that there is no resonance when the backup pump is in operation, but resonance occurs when the main pump is running. If the issue lies in the inlet pipelines, then it must be related to those 1.5-meter-long pipelines of the main pump; however, there is only one inlet valve on those 1.5-meter-long pipelines. We’re confused now; we don’t know what the reason is!
Judging from the phenomenon of the outlet valve closing, it’s possible that cavitation is occurring; pay attention to increasing the inlet flow rate and check. Increasing the inlet diameter reduces inlet flow loss.
Check the inlet valve of that pump; it might be clogged or have its core detached!