When Vibration Masks the Real Problems

Vibration spectral analysis and modal analysis are tools that designers and plant staff can use to troubleshoot their pumping systems. These sophisticated tools were used to diagnose and solve operational and mechanical issues at a two-stage raw sewage pumping station constructed in 1972 and have been upgraded twice since then to achieve its current 227 ML/d (60 mgd) design capacity.The modal and vibration analysis did result in resolving an intermediate bearing support structure resonance issue, but also uncovered other hydraulically induced vibration issues not diagnosed in previous studies and testing. Operating with two different diameter impellers in each of the two stage pumps contributed to vibration issues as did operating outside of the pump’s preferred operating range (POR) aggravated the vibration issues.