Authors: David Leslie, Manager, Oak Lawn Water Department; Jeff Buescher, Split Case Product Manager, Pentair; and Gary Patterson, Pump, Fan, and Compressor Technical Specialist, Dynamatic / Drive Source International, Inc.
Day after day, thousands of people drive through the intersection of 163rd & Central Avenue. It’s a good bet that hardly any of them realize that just a few feet below the intersection there is an underground booster station that sends drinking water to almost a quarter of a million people in the Chicago suburbs. This booster station, owned and operated by the Village of Oak Lawn, assists the two main stations in providing water to 330,000 people and helps Oak Lawn overcome the elevation difference between themselves and their customer communities.
The expansion of Oak Lawn Booster Station #2 involves the installation of two vertically-mounted split case centrifugal pumps, supplied by Pentair. The pumps are rated for 6000 GPM at 80 ft. total dynamic head. Each of these Pentair Fairbanks Nijhuis vertical split case pumps, model 10” 2844A with 14”x18” Turbo Free Elbows, is equipped with a Dynamatic® eddy current drive which operates with a small, digital controller. The combined eddy current drives and 150HP 1200 RPM motors are mounted on top of the vertical pumps with the support of fabricated steel structures to accommodate the weight and rotating load of the equipment.
These incoming units are identical to the existing 3 units which have been operating in the Oak Lawn Booster Station since 2010.
The Pentair 10”2844A pumps were selected for the original installation because of the following reasons:
Performance – The energy required to move 6000 GPM is significant, and over the life of the booster station every percent of efficiency matters. The Pentair 10”2844A are over 85% efficient at the design point, and 88% at their best efficiency point, helping to minimize the total energy consumed. To further reduce the total energy losses of the system, Pentair also supplied their Turbo Free elbow with these pumps which provide the performance benefits of a long radius reducing elbow in the space of a short radius elbow.
Footprint – Due to the layout of the pump room, space is at a premium. To overcome the space issues of traditional horizontal split case, the Fairbanks Nijhuis pumps were mounted vertically, reducing the required floor space by over 40%. Additionally, the Pentair Turbo Free elbows provide the same performance of a traditional long radius elbow in the footprint of a short radius elbow, saving an additional 5” of total length, without the reduced performance of a short radius elbow.
Durability – Pentair Fairbanks Nijhuis is known for providing long lasting durable pumps. Since their install in 2010, these pumps have not required any maintenance or service beyond what is typically required.
Materials of Constructions – Since these pumps are supplying drinking water, they were built using stainless steel wear components such as the wear rings and shaft sleeves and nickel aluminum bronze impellers for resistance to chlorination in the water as well as eliminating lead from the main components in contact with the water.
The Dynamatic® SPMV-AT-440 vertical eddy current drives had been selected in 2010 because they met four critical requirements:
1. Temperature – The Dynamatic® eddy current drives were selected over variable frequency drives (VFDs) because they eliminate the need to install air conditioning units into the booster station. VFDs commonly require owners to install air conditioning where it otherwise is not needed in order to keep the VFDs sufficiently cooled. Eddy current drives, on the other hand, do not require additional air conditioning. The #2 Booster Station does not have much cooling air, and the eddy current drives would not overheat in such a small space.
2. Size – There is not a lot of room in this underground booster station, so it was important to select equipment that fit in the unmanned station while still allowing room for inspection and maintenance.
3. Ability to adjust for changes in flow and pressure – Pumps that operate in booster stations often run continuously. The main reason for using variable speed is to adjust for changes in flow and pressure; which is the case for most booster stations. Booster stations are often working to maintain pressure to the system, regardless of flow. The eddy current drive adjusts speeds of the pump according to the demand of the control system. If a pressure drop is sensed, the unit turns on or speeds up the other pump to maintain the pressure in the system.
4. Noise – Noise is always a concern when you have a booster station situated in a residential area. While eddy current drives make some amount of noise, VFD-driven motors typically whine at a loud pitch; so noise considerations had been made during the initial evaluation of drive options. In the photo above, noise escapes through the green ventilating shafts coming up out of the booster station, which runs the entire length of the sidewalk. While noise levels can be difficult for engineers to predict, the original units have been proven to operate with acceptable noise levels.
Municipalities are required to have enough redundant capacity to meet pumping requirements, which is why this #2 Booster Station needed to be expanded. The expansion, which is financed in part by the Drinking Water State Revolving Fund, will enable the Village of Oak Lawn to provide more water to residents with greater reliability. “The peaking factors we have to meet are roughly 2.0 which allows you to double the demand on peak days. We cannot meet the 2015 peaking capacity using the rule of firm capacity, meaning largest pump at each station is taken out of service,” explains David Leslie, Manager of the Oak Lawn Water Department. “The 2015 allocations total is 40.07 million gallons per day and the 2030 allocation is 48.14 million gallons per day.” The addition of these new units, scheduled to be installed in 2017, is projected to accommodate the upcoming need for increased capacity.
Since 2010, the Nijhuis pumps and Dynamatic® eddy current drives have operated reliably in the #2 Booster Station, exhibiting long service life and low maintenance for the Oak Lawn Water Department. When it came time to expand the station, it was an easy choice to add two more of the exact same units, which are projected to provide the same reliable performance as demand for clean drinking water grows in the Chicago suburbs.
DOWNLOAD THE TECHNICAL PAPER: Efficiency, Life Cycle Cost, and the Eddy Current Drive. This technical paper discusses evaluation of life cycle costs, eddy current drive characteristics,
drive system acquisition, installation, and operating costs, annual savings comparisons, power factor, downtime, maintenance, and repair costs, and system efficiency.
Dynamatic® is an application-engineering and drives-manufacturing company specializing in Eddy Current electromagnetic drive technology solutions. Dynamatic electromagnetic drives can often be demonstrated to be the lower-cost alternative to variable frequency drives, notably in medium voltage water and wastewater pumping applications. To learn more, visit www.dynamatic.com.
Pentair plc (NYSE: PNR) is a global company dedicated to building a safer, more sustainable world. Pentair delivers industry leading products, services and solutions that help people make the best use of the resources they rely on most. Its technology moves the world forward by ensuring that water is plentiful, useful and pure, and that critical equipment and those near it are protected. With 2016 revenues of $4.9 billion, Pentair employs approximately 19,000 people worldwide. To learn more, visit pentair.com.
About the Village of Oak Lawn
Incorporated in 1909, the Village of Oak Lawn is a southwestern suburb of Chicago that is located in Cook County, Illinois. To learn more, visit www.oaklawn-il.gov.