Three Decades In Georgia – Screw Pumps Show Their Strength

With almost 30 years and counting of uninterrupted service for its 60” and 72” screw pumps, operators at the City of Calhoun’s Wastewater Treatment Plant have firmly underlined the benefits of basic preventative maintenance.

In 1988, Calhoun’s WWTP (permitted for 16 MGD) first invested in two of Lakeside Equipment Corporation’s 60”, 75 Hp open screw pumps (capacity = 7,000 gpm), and two 72”, 50 Hp screw pumps (capacity = 10,500 GPM). Original concrete construction involved an empty space provided for a third pump for each capacity, which was filled in 2012 by a new 60”, 75 HP Lakeside screw pump with a lift of 20.46 ft at 38ᵒ incline.

A year later in 2013, one of the original 60” Lakeside pumps was finally replaced (followed a year later by another of the same diameter to replace the last, original 60” screw pump) - but even then, as John Banks, City of Calhoun Wastewater Plant 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 said, “far from it. The original 60” Lakeside Screw Pumps far exceeded their life expectancy”.

The average flow at Calhoun (one hour north of Atlanta), is around 5MGD (14-16 MGD 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. 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 12 years) added:

“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 25-years-plus, which shows what a good investment they are”.

Normally, two of the Lakeside screw pumps at the influent of Calhoun’s WWT Plant 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.

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 continued: “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 preventative 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”.

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 concluded: “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 & 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, visit www.lakeside-equipment.com.