Analysis of the regular fluctuation of the 2nd harmonic vibration of mechanical pumps

Thread Content

Recently, I encountered two pump units: one with dual supports and the other cantilevered. Both used diaphragm couplings. After replacing the mechanical seals (without changing the bearings), vibration levels were found to be excessive during trial operation. The horizontal and vertical vibration levels for the unit with dual supports, as well as those at the drive end and the non-drive end, were all significantly high (8.9/9.3 mm/s), with fluctuations of around 1.5 mm/s. For the cantilevered pump, the horizontal vibration level on the side connected to the coupling ranged from 7.8 to 9.4 mm/s. When analyzing the vibration spectrum, the first harmonic accounted for about 60% of the total vibration, while the second harmonic accounted for 40%; the fluctuations were mainly in the range of the second harmonic. The pump was shut down again to check the diaphragms and alignment, but no abnormalities were found. Yet the vibration problem persisted. The bearing acceleration was not very high, at 16 mm/s, with a GIE value of 1.2. I would appreciate it if anyone could help analyze this situation