[Help Request] We have a magnetic pump that experiences high vibration levels; please help identify the cause
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Magnetic pump, with NPG melt as the medium; pump body temperature of 120°C, speed of 2900 rpm, impeller diameter of 230 mm; inlet pressure of 0.018 MPa and outlet pressure of 0.66 MPa; connected via diaphragm coupling. During the first operation, the pump head leaked; the gaskets were replaced, as well as the sliding bearings and rolling bearings. There was slight wear on the inlet guide vanes. Due to restrictions imposed by the motor feet, the horizontal alignment was off by 1.5 mm, with a misalignment of 0.5 mm. Vibration was observed at 5 levels when the pump started up. During the second operation, the bearings and impeller were inspected and found to be in good condition. However, there was a significant deviation between the center of the impeller and the inlet sleeve: the upper gap was 2 mm while the lower gap was 0.15 mm. The inlet and outlet components were removed in order to realign the pump head. Due to high stress in the inlet and outlet pipelines, the horizontal alignment remained off by 0.70 mm after tightening, with a misalignment of 0.3 mm. Vibration was still observed at 5 levels when the pump started up. The frequency spectrum measurements are as follows; please help analyze them
Consider several issues: 1. Pump selection – whether the medium provided meets the required net positive suction head of the pump； 2. How is the pump’s dynamic balance? ； 3. Was the installation carried out in accordance with the manufacturer’s requirements?
First of all, the structure of magnetic pump ensures good stress resistance, low deflection, and extremely minimal vibration! ! It is initially believed to be a installation issue; they should all have been tested before leaving the factory. Has the base become deformed? Loosen the inlet and outlet pipes of the pump to check whether the pipes are installed properly If it was installed by forceful pulling, the pump is likely to be deformed. It’s unclear whether the inlet pressure you’re referring to is absolute or gauge pressure; what is the NPSHa value? Pump flow rate? Can cavitation be ruled out?
The coupling compensation limit for JM1 is 2.5 mm, so this is not the main reason
The several identical pumps nearby are working fine; however, the 1st, 2nd, 3rd, and 4th harmonic frequencies shown in the spectrum are all on the high side. The possible causes are complex, and dynamic imbalance is likely an issue.
The stress at the inlet and outlet is currently very high; the base has been checked and shows no issues, so it is suspected that the pump head is deformed.
I’ve been serving users for so long that I don’t dare speak harshly to them: lol. The pump has been disassembled; let’s check its geometric tolerances to see if there’s still any way to fix it. Otherwise, installing it will still cause the brothers to waste effort for nothing
If the vibration is severe, consider the following issues: the stress on the pipelines is relatively high; it is recommended to reconfigure the pipelines or adjust the pipe supports. Secondly, a dummy shaft should be used to verify the dynamic balance of the impeller; thirdly, it is necessary to check whether the alignment is satisfactory and whether there is any damage to the laminations.