Calhoun’s treatment plant benefits from long-lasting open screw pumps
With almost thirty years and counting of uninterrupted service for its 60-inch and 72-inch screw pumps, operators at the City of Calhoun’s Wastewater Treatment Plant have firmly underlined the benefits of basic preventive maintenance.
In 1988, Calhoun’s WWTP (permitted for 16 million gallons per day) first invested in two of Lakeside Equipment Corporation’s 60-inch, 75 horsepower open screw pumps (capacity of 7,000 gallons per minute), and two 72-inch, 50 horsepower screw pumps (capacity of 10,500 gallons per minute). Original concrete construction involved an empty space provided for a third pump for each capacity, which was filled in 2012 by a new 60-inch, 75 horsepower Lakeside screw pump with a lift of 20.46 feet at 38-degree incline.
A LOOK INSIDE THE WASTEWATER TREATMENT PLANT
A year later in 2013, one of the original 60-inch Lakeside pumps was finally replaced (followed a year later by another of the same diameter to replace the last, original 60-inch screw pump)—but even then, as John Banks, the City of Calhoun Wastewater Treatment Plant’s manager, explains, this was more to do with budgetary and long-term planning requirements.
“The pumps were only just beginning to wear out, but they were certainly not on their last legs,” he says, “far from it. The original 60-inch Lakeside Screw Pumps far exceeded their life expectancy.”
The average flow at Calhoun (one hour north of Atlanta), is around 5 million gallons per day (14 to 16 million gallons per day during rain events), serving the city of Calhoun, Georgia (home to some of the world’s top floor covering manufacturers). The treatment plant is a tough, corrosive environment for the original Open Screw Pumps (all Lakeside), that via three different configurations, run rotationally 24/7 to equal out wear.
Lakeside’s open screw design utilizes a torque tube and spiral flights
SCREW PUMPS GET TO WORK
Consisting of a spiral screw, upper and lower bearings, and a drive arrangement, the open screw design uses a torque tube with spiral flights set in an open, inclined concrete trough. The screw pump’s basic design has been used for millennia to promote both simplicity and reliability.
John Banks (who has worked at the facility for twelve years) adds, “The beauty of the Lakeside screw pumps is that there is actually very little maintenance. Once per week we check oil levels and our operators will also monitor the grease levels on the bottom bearing. All very simple—and with Lakeside’s stainless steel tubing, we don’t have to worry about corrosion. These routine checks have seen our screw pumps work very reliably for twenty-five years-plus, which shows what a good investment they are.”
Normally, two of the Lakeside screw pumps at the influent of Calhoun’s WWTP lift the raw sewage up out of the collection system into the plant. Pre-screening is not required because large objects pass between the screw flights and through the screw pump.
BACK-UPS AT THE READY
Additional screw pumps are ready in the event of the sewer system becoming supercharged due to a large rain event. After lifting, the wastewater is taken through screening and grit removal processes before being lifted again by a second set of screw pumps.
John Banks continues, “Our program of rotating the use of the screw pumps, combined with basic oil checks and free-flowing grease has given us a winning hand of flexibility and very long-lasting equipment. This preventive maintenance program also means that we don’t have the pressure of having to get a screw pump back into service quickly if and when we are looking for additional pumping capacity.”
A V-belt drive protects against possible shock loads
THE MORE THINGS CHANGE
The older portion of the Calhoun system covers over 136 miles of interceptor and trunk lines through the city. It was upgraded in 2004 to meet new standards.
Then, as now, the purchase of screw pumps was put out to bid, with an eye on securing the best in long-term performance and value. Lakeside offers both greased and sealed lower bearings on their open screw pumps. The dual upper bearing of each style pump includes both radial and thrust components, serving both forces that act upon it, which helps prolong the lifetime of the screw pump. The pump also benefits from a V-belt drive that connects the motor to the speed reducer. This acts as a shock absorber to protect from possible shock loads, as well as provide for easy speed changes in the field. The constant speed drives eliminate the need for complex, variable speed electrical controls.
John Banks concludes, “We’ve taken care of our screw pump installations, but Lakeside are always there to help with start-up, and service if required. They’re a company that very much stands by its equipment, and like us, thinks about the long term. We’ve also had good support from Lakeside’s representative Templeton and Associates, based in Suwanee, Georgia.
“We see good grease coming out during our checks, which means we have good grease in there for these very robust screw pumps. This plays a big part in the continuing smooth-operation of our plant.”
FOR MORE INFORMATION
Lakeside Equipment Corporation is an engineering and manufacturing company concentrating on helping to improve the quality of our water resources. Lakeside started in the spring of 1928 to engineer, develop, and provide water purification systems to municipalities and companies throughout North America. For more information, visit
www.lakeside-equipment.com.
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MODERN PUMPING TODAY, July 2018
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