Niantic Wastewater Pump Station Upgrades: A Case Study in Vibration Analysis and Collaborative Solutions

The Niantic Wastewater Pump Station, constructed in 1992, is a vital component of East Lyme’s wastewater management system. It facilitates the conveyance of all wastewater flows (Approx. 1 MGD) across the Niantic River to Waterford, where treatment occurs at the New London Wastewater Treatment plant. Notably, the Niantic Pump Station is the largest among East Lyme’s 24 pump stations.

The Niantic pump station was built with 4 Cornell 150 HP Drive Shaft Dry Pit wastewater pumps. Since its original construction, two of the original pumps were replaced on an emergency basis by two 115 HP Sulzer dry pit submersible pumps rated for 1800 GPM at 155-ft TDH. However, after the installation of the two new pumps, there were vibration issues leading to repeated bearing failures. After extensive analysis by East Lyme Water & Sewer Staff and Mechanical Solutions, Inc it was determined the root cause of the high vibration of the pumps was due to a resonance of one or two structural natural frequencies. The structural resonance describes side-to-side twisting motion of the pump volute due to excessive flexibility of the pump supporting pedestal.  The motion at the top of the motors was reacting out-of-phase from the volute motion as a rigid body.  These natural frequencies are excited by the vane pass frequency (VPF) forcing function at 2x rpm towards the upper end of the running speed range.

 

 

 

 

 

 

 

 

To address the issue effectively, the solution involved shifting the structural frequencies above the VPF range by stiffening the supporting pedestal. This was achieved through the installation of concrete piers and a soleplate to provide robust support for the pumps. The comprehensive solution also entailed the redesign and construction of the pipe layout and concrete pier structure, executed by Tighe & Bond and RH White Construction respectively. Additionally, the project included the installation of new Variable Frequency Drives (VFDs), flow meter, valves, updated instrumentation, controls, and an 18-inch line stop for enhanced operational flexibility and control.

The successful execution of the project was a collaborative effort, with the East Lyme Sewer Department serving as general contractor and project manager. Their responsibilities included procuring and overseeing various aspects of the project, including electrical, instrumentation/SCADA, sitework (line stop), bypass pumping, mechanical piping, and pump installation. The involvement of multiple stakeholders ensured seamless coordination and timely completion of the project.

Funding for the project was sourced from a combination of American Rescue Plan Act (ARPA) funds and East Lyme’s Sewer Assessment fund. This financial support was instrumental in implementing the necessary upgrades and improvements to the Niantic Pump Station, thereby enhancing its resilience and efficiency.

In conclusion, the successful resolution of the vibration issues and upgrades to outdated technology at the Niantic Pump Station underscores the importance of proactive maintenance and infrastructure upgrades in ensuring the reliable operation of critical wastewater facilities. Through careful analysis, innovative engineering solutions, and collaborative project management, the project not only addressed immediate challenges but also bolstered the station’s capacity to meet the evolving needs of the community. Moving forward, continued investment in wastewater infrastructure will be essential for safeguarding public health, protecting the environment, and promoting sustainable development in East Lyme.