Analysis of the reasons for high vibration in single-stage double-suction centrifugal pumps
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Hello, expert! Our company has a single-stage, double-suction centrifugal pump that has experienced high vibration levels since it was first put into operation in September 2015. The fluid handled by this pump is MDEA (a lean liquid pump); its power rating is 650 KW, the inlet pressure is 0.1 MPa, and the outlet pressure is 3.8 MPa ； The pump schematic diagram and vibration spectrum are shown below; we hope experts can help analyze the cause of the vibration Thank you!
Does this LZ pump come with a gearbox? What form? It’s quite rare for the dominant frequency to reach the 5th harmonic; there aren’t many factors that could explain this
Watching, waiting for an expert: lol~~~
Check the time-domain waveform to see if the pump’s sound is normal; static and dynamic friction are suspected
Without a speed increase gearbox, the pump is driven directly by the motor; the coupling used is a diaphragm coupling. The pump is a single-stage, double-suction centrifugal pump. Both bearings at the ends of the rotor are SKF rolling bearings – the radial bearing on the drive side is of the SKF6213 type, while the thrust bearings on the non-drive side are two SKF7311-type bearings mounted back to back.
Being this tall vertically must be related to the foundation. The main component of the vibration is the impeller passing frequency, indicating that the impeller is slightly eccentric. A comprehensive analysis of these two factors suggests that it may be related to an uneven pump foundation; the tightening of the bolts can cause deformation of the housing, and in some cases it can also lead to damage to the bearings. The fastening bolts of the shoulder can be loosened at runtime, one by one, to observe the changes in vibration.
For this rotor, it is necessary to perform dynamic balancing at least up to level 3. It is advisable to use bearings with copper cages, and it’s best to choose genuine NTN or NSK brands. I hope this helps.
This pump has a very high head and high power; it belongs to the category of centrifugal pumps that are near or have reached their design limits. The impeller diameter is likely around 500. Based on the selection of bearings, it can be seen that the shaft of this pump has relatively poor stiffness. Additionally, certain structural parameters of the impeller and the casing may not be properly matched, which results in significant vibrations at the frequency of the blade passage. Over time, cracks may appear at the junction between the shaft and the impeller’s keyway. If that’s really the case, it’s very difficult to solve the problem simply. When buying or selecting a pump, a reasonable solution is key; reliability comes first – don’t go for the cheapest option. Should this pump be a two-stage pump or a multi-stage pump? The stiffness of the shaft is also important.