Ada Township – a community with a population of approximately 13,000 – is located several miles east of Grand Rapids in Kent County, Mich. The township owns and operates its own sanitary sewer collection system and is responsible for all maintenance and replacement. The majority of the collection system flows by gravity to a pump station, where it is sent to the City of Grand Rapids. Total flow is approximately 1 mgd.
Scope
Ada’s main pump station had become unnecessarily complex over the years. For example, the pumps had so many moving parts that they had become very expensive to maintain. The old pumps were constantly under repair. Seals were always failing, and vibrations were so bad that the pumps had to be held down with sand bags. When excessive vibration and seal failures became chronic, Ada Township knew it required a new approach to the problem or its budget was going to take a major hit.
After huddling with its consultant, Moore & Bruggink, Ada and its engineering firm contacted Kennedy Industries for assistance. Working off their extensive experience with Xylem’s dry pit submersibles, the professionals at Kennedy immediately recommended the installation of three Flygt model 130-hp NT-3315s to deliver 1,400 gpm at 205 ft of total dynamic head.
Solutions
The pumps were changed out one unit at a time. First, one of the old pumps was removed, along with its shafting, pillow block bearings, guards, seal water pots, seal water piping, air compressor lines, air compressor and vertical motors. New pump installation was easy because these dry pit submersibles do not require a seal water system, coupling, shafting, guards or any other auxiliary items.
The pumping assembly is designed for continuous operation in either a non-submerged or a fully submerged environment. The motor is inverter-rated per National Electrical Manufacturers Assn. MG1, Part 31, and is available as premium efficient. Variable frequency drives and air-cushioned check valves were also added. A Hard Iron (25% chromium) impeller and insert ring are standard on all the company’s pumps above 10 hp.
The dry pit submersibles also provided maintenance advantages over the township’s existing pumps, saving it $5,000 to $6,000 annually since installation that was previously spent on unscheduled visits to the main pump station. For example, the dry pit submersibles feature:
- N-technology impellers – These impellers are self-cleaning, raising efficiency and reducing unplanned maintenance visits. Stringy fibrous material and modern trash that enter the inlet of a conventional pump often get caught on the leading edges of the impeller vanes, reducing efficiency and increasing power consumption. In addition, should solids continue to build inside the impeller, motor thermal protection can trip and cause the pump to stop, all of which leads to expensive unplanned service calls.
- Inspection chamber – To increase operational reliability, an inspection chamber between the seal unit and the bearings enables rapid spot checks and maintenance.
- Active Seal – The Active Seal system is a zero-leakage double-seal system that actively prevents liquid from entering the motor cavity, thereby reducing the risk for bearing and stator failure.
Finally, since the new pumps are submersible, they would remain undamaged if the station floods, unlike the previous pumps. Also, operator safety has been dramatically improved since operators no longer have to maintain 25-ft-long shafting or frequently remove the pumps for repair.
Results
Greasing motor and pump bearings, shaft maintenance and shaft U-joint alignment and balance are all tasks of the past. Ada Township is now the owner of three new submersibles that run smoothly and quietly. In fact, an operator recently reached into his pocket and pulled out a nickel. He then stood it vertically on end while the pump was running; hours later the nickel was still in the exact same position. It is safe to say that these three dry pit submersibles will provide the township with reduced maintenance and no unnecessary repairs for many years to come.
