From OEMs to municipalities, every sector along the pump industry’s path is seeking more sustainable approaches to traditional operations. Below, SWPA Executive Director Adam Stolberg and Liberty Pumps’ director of engineering, David M. Williams, discuss how the combination of electric motors with submersible pumps has proven a reliable, cost-effective, and versatile option for many pump users.

As the push toward greater efficiency continues, where do you see electric motors expanding in the submersible pump market?

Ongoing design advancements and the resulting efficiency improvements being achieved in electric motor design will support continued growth in the use of AC electric motors in submersible pump applications. As pumping applications make up a significant portion of the world’s overall energy consumption, it is critical that users and manufacturers continue to work together to optimize pump system design, selection, and utilization. In addition, ongoing advancements in controls such as VFDs (variable frequency drives) allow further tuning and optimization to meet exact system requirements while maximizing efficiency.

Are there horsepower ranges available in today’s electric motors that weren’t possible in the past? 

AC electric motors have always been available in a wide range of horsepower levels, but advances in design and manufacturing techniques have supported continued growth in higher horsepower submersible pump applications. Lately, several manufacturers have been developing larger horsepower submersible grinder and chopper pumps to help combat today’s modern wastewater challenges.

How do you convince the skeptics wary of combining electric motors with submersible applications? 

Decades of successful AC motor use in submersible pump applications is indisputable evidence that the technology is both proven and reliable. The specific benefits, as we discuss later, come together to ensure that users can be confident that that a properly selected submersible pump will provide a long-term reliable solution to their wastewater pumping needs.

What makes electric motors such a versatile power source for submersible pumps? 

Electric motors are the ideal power source for submersible pumps because pump manufacturers can work with motor designers to develop motors with power curves tailored for the specific load points, and also incorporate custom motor shafts which serve as the main shaft for the pump wet end.

How would you best describe the benefits of using an electric motor in submersible pump application? 

There are numerous benefits related to incorporating the electric motor into the pump design that facilitate installation and minimize or eliminate maintenance. With the motor and pump sharing a common shaft, issues such as motor mounting and alignment are eliminated. Further, as submersible pumps are hermetically sealed and most are oil filled, there is no need for periodic bearing maintenance or lubrication, and the circulating oil efficiently transfers heat to the housing, which is then cooled by the pumped media going through the volute as well as surrounding the pump in the wet well. The motor is also inherently protected from damage that could occur during floods or other events.

How do those benefits extend over the life-cycle of the pump? 

With the motor isolated from contamination or damage, protected from heat through efficient and uniform cooling, and with bearings and seals permanently lubricated, the ongoing maintenance activities and related costs are minimal and lead to significant long-term savings over the life of the pumping system.

What are some of the best ways to assess true efficiency for submersible pumps and electric motors? 

Pump manufacturers generally provide efficiency information in one of two ways—either pump (hydraulic) efficiency, which is the efficiency of the pumping portion of the device, or “wire-to-water” efficiency, which takes into account the total amount of energy consumed by the pump including heat, friction losses, etc. Either method provides useful information when comparing various pumping solutions, but the key is to ensure that you are looking at all options using the same method, and then focusing on the solution with the best efficiency point where it meets the system curve.

For pump users shopping today for an electric motor, what are some of the features you’d recommend they consider? 

With an ever-increasing focus on energy efficiency, I’d encourage pump users to look for motors that are constructed per NEMA® IE3 Premium Efficiency standards and suited for inverter duty applications with proper shaft grounding for use with VFDs (for larger horsepower applications). As always, SWPA encourages users to take the Systems Approach to pump station design. It is critical to ensure that the motor/pump/system combination is properly designed for the application to maximize efficiency and ensure long-term and trouble-free operation.


SWPA is the industry’s leader in providing accurate, up-to-date technical information about submersible wastewater pumps and the component parts and accessories in lift stations using solids-handling pump systems. Now in its fourth decade of service, SWPA has become the recognized voice for the submersible pump segment of wastewater industry and looks proudly upon its long legacy of service. For more information or to join, visit

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