It’s oh-so-quiet at the Mahanoy City Wastewater Treatment
Plant in Pennsylvania.
Unless you’d been told otherwise, you wouldn’t know that close by, a 36-inch diameter pump is operating night and day in a giant concreted basin.
And even when one of the two larger screw pumps (84" diameter) is also being put through its paces, remarkably there’s still a kind of a hush.
With the town’s school district just 300 feet away, this very well-run treatment plant is a good neighbour.
Today’s calmness though is quite an altogether different story from previous dramas experienced at Mahanoy City WWTP. The original 36" diameter raw sewage enclosed screw pump, which had become increasing unreliable, failed twice, ultimately giving the plant operators no option but to look for a more sturdy and efficient alternative. The heavy-duty enclosed Type C screw pump from Lakeside Equipment Corporation was chosen – a design with two convoluted flights that are welded to the rotating outer tube, with the lower bearing mounted above water level.
Mahanoy WWTP’s Assistant Chief Operator, Josh Ball, commented: “Through Lakeside’s representative Doug McCord in Exton, PA, we’d always had a very good relationship – and with this new enclosed Type C screw pump we immediately benefitted from an intelligently designed and very well engineered product.”
Two years later though, one of the original 84" diameter enclosed internal-lift type screw pumps suffered a catastrophic failure, forcing the operators to introduce a temporary (three-months) bypass system.
“At the time, this was pretty nerve-wracking,” added Josh Ball.
“The bolts on the stainless steel ring, on which the vast majority of the weight rests, simultaneously broke, causing the structure to break in half. It was scary.”
For storm events, the town has to have sufficient back up capacity, so the decision was taken to replace both of the larger pumps – and Mahanoy City had little hesitation in deciding to replace
the old units with two brand new 84" diameter enclosed Type C screw pumps to line up alongside the 36" diameter pump that had been working without any issues for the past 24 months.
The two new larger screw pumps, utilized alternately during heavy rainfall, have so far only been needed for flow rates of two million gallons per day, though they can handle a total of 50 million gallons per day. Installed in the wet well at an angle of 38 degrees, these larger pumps sit next to the workhorse 36" diameter pump that on average handles 850,000 gallons per day, but can go up to 1.38 million gallons per day.
Designed for trouble-free operation, with options for either an open or enclosed design, the new Screw Pumps lift large quantities of water or wastewater at low heads for applications such as return activated sludge or storm water pumping. The Open Design consists of the spiral screw, upper and lower bearings and a drive arrangement, using a tube and spiral flights set in an open, inclined trough that permits both simplicity and reliability.
Lakeside’s Enclosed Screw Pumps utilize the same operating principles, but are encased within a tube and use either rotating or stationary outer tubes inclined at up to 45°, allowing the shortest horizontal space required for a given lift.
The enclosed Type C 84" diameter screw pumps, which were a drop-in replacement for the failed original internal-lift type pumps, have allowed the plant to get back to normal for the 4,000 residents of the town (plus 2,800 at a local state prison).
Once at the heart of the coal industry, Mahanoy City’s wastewater that goes through to the combined sewer overflow, is all from domestic use.
‘Only stainless steel
that ultimately survives’
“In this volatile environment, it is only stainless steel that ultimately survives,” added Josh Ball, who has been working at the plant since he was a teenager almost two decades ago.
Doug McCord added: “We aimed to bring about the best and most long-lasting solution for Mahanoy City. This scale of pump installation is a significant investment and needs to be applied with the utmost precision. Lakeside used all of its vast engineering, fabrication, machining and aligning experience to bring about a truly first class job.”
The smaller of the pumps, which is installed in the deeper part of the wet well, has required only minimum maintenance since its installation – a weekly treat of oil and grease, plus a change of oil just twice per year. For the two new larger screw pumps, an oil change is required just once per year.
“We do of course carry out regular visual inspections,” continued Josh, “but all three enclosed Type C pumps are extremely reliable. Doug and Lakeside are helpful as well as consistent, and always apply common sense.
“Compared to the previous cross-start motors on the old pumps, the Type C’s are also more efficient, using far less energy. When needed, the capability of these pumps also gives us the advantage of being able to clean out the well without going over the bearings. The power is there to bring it down to operating levels very quickly.”
He added: “We have a new soft start-up with 200 HP motors, but it is incredible that the Lakeside pumps are so quiet. In fact, when we first had them installed, we couldn’t hear anything, so we had to go outside to check that they were running! If we’d had loads of noise from the start-ups and constant humming, it could have led to possible complaints from the school district that’s so close to us, but because of the very high quality work by Doug McCord and Lakeside, everything is running smoothly and quietly. The difference between how the old pumps used to sound is like night and day – and we’ve also seen a big improvement in reliability.”