The management of a 28 mgd potable water system at the Rogers (Ark.) Water Utilities recently reported it has installed a customized, prefabricated pump station to enhance reliability for a long-needed emergency storage capacity upgrade.
Selection of the prefabricated station, manufactured by Flowtronex PSI Inc., an ITT Industries company, was regarded as a highly desirable alternative to purchasing station components separately and assembling them at the site. “We have been short of emergency storage in our water system for a long time, and there is no end in sight to the rapid population growth in our service area,” said Tom McAlister, superintendent of the Rogers Water Utilities. “We had only 1.5 million gallons of ground storage and 4.5 million gallons elevated. Our 1996 engineering study showed a need for an additional eight million gallons in-ground and another two million elevated to meet the health department’s guideline of a day’s worth of usable storage in case of a supply interruption.
“We couldn’t put all we needed above ground because the expense was prohibitive, and the prefabricated option for the pump station provided the reliability we wanted for the underground addition.”
McAlister went on to say that his plant’s system averages 7.5 mgd to about 21,000 metered users—with 60% residential and the balance commercial/industrial.
Resolving issues
The water disbursed by the Rogers Water Utilities is purchased from a wholesaler who pumps to the elevated tanks that provide system pressure for all distribution. Resolution of complex operational issues with the communities delayed the deployment of the underground storage addition until last December, when the prefabricated 15,000 gpd capacity Lilac Street Pump Station was delivered. The underground tank was scheduled for installation concurrent with WWD’s presstime.
“When we saw the Flowtronex station at a conference, advertised as prefab to spec, prewired with all the PLC’s and VFD’s in place, it made a lot of sense from a construction standpoint—much better than stick-building it up on site,” McAlister said. “They shipped it to us on five skids. All we had to do was bolt it together and hook it up to power. The station was designed to meet maximum day demand and was plumbed to add a second ground storage tank in the future.”
“When an operation is as complex as ours, with inputs from a SCADA system and automation of level and pressure sensors, we knew from experience that if complex controls were properly integrated with the pump station, we would have less problems,” he continued. “When you look at the control panel, you see each pump has its own PLC and VFD, and there are literally thousands of wires. The manufacturer committed to working with the general contractor to get all the inputs and controls right.”
“We liked their capability to build it and make it work, almost like a plug-and-play,” McAlister added. “Even though we could’ve found a contractor to stick-build at the site, we knew most of them weren’t good at all the needed expertise and offered only a combination of strengths and weaknesses. Flowtronex’s strength was building it in a controlled environment in their own manufacturing facility, wiring in the PLC’s and VFD’s at the same time, and painting in a climate-controlled paint booth instead of on site in the cold weather. They also saved us a lot of engineering time that was needed for other projects.”
Stephen Ponder, a design engineer for the utility, said the vendor’s design assistance was greatly appreciated. “I set up a visit to their plant for our superintendent, our chief of engineering and our director of operations,” he said. “We wanted the capability for pumping 5,500 gpm into the system to refill elevated tanks, and we simply provided the flow and head conditions and other data for their worksheet. They designed around our specs, including sketching the piping arrangement, with everything going into the bid document.
“They provided single-source responsibility for a lot of complicated stuff. We knew doing it otherwise as a stick-build invited finger-pointing when things didn’t go right. It didn’t seem to be a big deal for them to reinvent the wheel each time they make one, and we were very confident in their capabilities.”
Factory-build approach
The Lilac Street Pump Station, shipped by truck as five separate skid-mounted modules, was built by Flowtronex in about six weeks from approval of submittals by the city. Total weight was about 65,000 lb. Dimensions of the final assembly are approximately 60 ft x18 ft.
While the company had built stations with higher flow range, the Lilac Street Pump Station was the largest in size it had fabricated to date.
A special need with this larger pump station, which went together as smoothly as a smaller one, was to customize the company’s standard variable frequency drives to be set up for control by another party’s SCADA system.
Accordingly, the contractor there took care of needs like preparing the foundation, erecting the building and bringing in power, while the station was being fabricated simultaneously at the plant. Thus, there was no installation delay for the building at the site.
