Vibration problem of the water pump outlet pipe
Thread Content
This post was last edited by mao8682995 on 2018-11-9 at 13:01. One single-stage, double-suction, split-case pump in our factory is of the model KQSN400-M9/526S, with a flow rate of 1900 m3/h and a head of 77 m. When it is in operation, the outlet pipe of DN500 experiences significant vibration, at around 30 mm/s. Previously, it was suspected that the foundation embedding bolts of the water pump were loose; after addressing this issue, a trial run was conducted again. The vibration of the outlet pipe remains quite high; the vibration at the anchor bolts embedded in the pump was measured at 0.06 mm/s, while the vibration of the pump’s own anchor bolts was 4.2 mm/s. Another issue identified was the significant axial movement of the water pump; when the pump was started but the outlet valve was not opened, it was possible to clearly see the shaft of the pump moving back and forth. After the outlet valve was opened, the axial vibration of the pump was measured at 8.8 mm/s. Could everyone please help analyze the reasons for the excessive vibration in the outlet pipe? . By the way, this vibration data was measured before secondary grouting was done.
Upload a photo of the pipeline layout at the site
Poor pipeline support can also cause vibrations in the pipelines; it is necessary to first ensure that the pipeline support is in good condition before determining whether the issue lies with the pump itself
The axial movement is clearly visible; is this bearing still functioning? If it continues to operate in this way, the pump will be damaged. There are generally three reasons for vibration in the outlet pipe: 1. High pump flow rate and high velocity, resulting in severe impact forces. In your case, the velocity is only 2.79 m/s, which is not high, so this shouldn’t be the cause. 2. An improper diameter change in the outlet pipe, incorrect placement of elbows, or valves that are too close to the pump, all of which can cause significant local impact forces. 3. Inadequate support and fixation of the outlet pipe. 4. The vibration in your pipeline is over 30 units – is it also in the axial direction? If so, it’s very likely caused by axial movement of the pump shaft
To elaborate further, there are a total of four pumps in the pump room, all of the same model, and the piping layout for these pumps is similar as well. There has never been such significant vibration in the discharge pipes before. Try reinforcing the support for the outlet pipe again and then test it
If there is no secondary grouting, it means the inlet and outlet pipes were installed without proper alignment; in the absence of secondary grouting, were the adjustment shims for the foundation bolts used to fix them in place? The installation procedure for this pump is completely incorrect; there is no secondary grouting, and the alignment performed at this stage is only a rough alignment. As a result, testing can damage the fixation of the foundation bolts, leading to an unstable primary grouting of those bolts. There are too many possible vibration factors. Another consideration is whether it will operate as a single unit or in a multi-unit setup; if operated in a multi-unit setup, pipeline vibration may occur. The main problem is that it was tried out while still only half installed – it was complete nonsense.
For single-stage double-suction pumps, it is also necessary to check whether the clearance of the bearing caps meets the standards. Additionally, it should be considered whether operating multiple pumps simultaneously leads to competition for flow, resulting in unstable pressure and shaft movement.