Water Treatment Plant Pumps Fail Vibration Specification During Commissioning

By October 20, 2016
Secondary Waste Activated Sludge Pump MEscope Model

A contractor putting together a water treatment facility for a large city in Colorado encountered vibration issues with various pumps during commissioning.  An independent opinion was required after multiple failed attempts by the OEM to fix the problem.Secondary Waste Activated Sludge Pump

  • Problem Statement (Challenge)
  • Work Performed
  • Results/ Solution
    • Findings: The root cause for the elevated vibration in the PEPS pumps was a pump bearing frame and shaft lateral resonant condition within the operating speed range at vane passing frequency. The RAS pumps had the first shaft lateral bending mode excited by vane pass frequency near the upper end of the speed range.  The SWAS pumps suffered from excessive flexibility between the bearing frame and the stuffing box leading to a bearing frame natural frequency in resonance, and also piping structural natural frequencies within the running speed range.
    • Impact: The contractor presented MSI’s findings and recommendations to the OEM to try and find mutually agreed upon solutions to the problem. The contractor avoided costly delay penalties by finding the root cause and not continuing to pursue the cut and try method.
Secondary Waste Activated Sludge Pump Operating Deflection Shape ODS

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Return Activated Sludge Pump Operating Deflection Shape ODS

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Primary Effluent Pump Operating Deflection Shape ODS

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Primary Effluent Pump Suggested Modification

PEP suggested modification

Return Activated Sludge Pump

RAS pump with OEM bracing modification

Secondary Waste Activated Sludge Pump Suggested Modifications Bearing Tower

MSI suggested bearing tower modification

Secondary Waste Activated Sludge Pump Suggested Modifications Discharge Pipe

MSI suggested discharge piping bracing