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The Dolan booster pump station, near Turton, S.D., was beginning to show its age. Maintained by the WEB Rural Water Development Project, the station had been operating continuously since it was put in service in 1989. But the pumping rates of the station’s two 10-hp end suction pumps had been falling off gradually for the past few years, and the recent addition of about 25 connections was making it even harder for the pumps to keep up.
“We monitor our pump stations with telemetry, and after evaluating all of the information that we had coming in, it was clear that the pumps were showing wear and that it was time to do something before all the excess capacity was gone,” said Mark Lindseth, WEB’s operations manager.
WEB decided to replace not only the end suction pumps, but their across-the-line starters and mechanical control valves as well. Weighing heavily on the decision of what to replace them with was the need to have the entire changeover completed without cutting service to any of the 200 customers served by the Dolan elevated tank. To keep service to all customers going, WEB had a limited timeframe, which was dictated by the amount of water left in the tank. “We figured we had about 24 hours at most,” Lindseth said.
Putting even more pressure on the project team was the fact that the upgrade would include the removal and replacement of all the piping inside the station. Because of its underground location, the station is subject to flooding, so WEB opted for stainless steel pipe. “That required us to remove everything from the station. We basically replaced all of the pumps, controls and plumbing,” Lindseth said.
Plenty of Time to Spare
As it turned out, the entire upgrade was completed in less than 10 hours, leaving plenty of water in the Dolan tank and no customers without service. Along with plenty of advance preparation, which included prefabricating most of the piping, the effort was facilitated by WEB’s decision to replace the end suction pumps with two 15-hp Goulds Surface Mount Vertical Turbine pumps with Aquavar centrifugal pump controls.
“The nice thing about the SMVT pumps is that you can just drop them into place without changing the can,” Lindseth said. “If you go to a traditional turbine, you have to deal with a can for the pump. But with the SMVT, it’s basically a bolt-in-place situation, since everything’s prepackaged.”
According to Lindseth, that was the only way to bring up a station in 24 hours without having to build a new station alongside the existing one and cut over to it.
“We could have tried to find another end suction pump that was close to the parameters we needed and try to go back to what we had before, but we’ve had such good success with other SMVT pumps that we decided this would be the better way to go,” Lindseth said. “We’re also familiar with the flange arrangement on the pump, which is one of the easier ways of installing a pump.”
Advantages Add Up
With a service area of about 5,450 sq miles, WEB is one of the largest rural water systems in the country. The organization’s 34 employees serve about 14,000 customers and maintain 145 miles of ductile iron main lines, 6,200 miles of secondary lines, 27 storage tanks and 30 telemetry-controlled booster stations.
WEB has used Aquavar controllers at about 10 other sites, and the group’s technicians have always found it easy to program the units for service. “Everyone does AC drives a little differently,” Lindseth said, “but the Aquavar programming and menus are tailored to make it easier to start up the drive. Standard AC drives may be used for everything from fans to conveyor belts, but the Aquavar variable speed pump controller is streamlined for pump applications. So, instead of taking a generic device and trying to make it work in a pumping application, it’s nice to have an off-the-shelf device that’s tailored toward pumping.”
But, as Lindseth points out, the benefits of the SMVT’s design and Aquavar controllers go far beyond ease of installation.
“We get all the advantages that the multi-stage turbine pump has over the end suction pump,” he said. “Some of our elevated tanks are 15 miles from the booster, so we have an awful lot of line loss in the system. But it’s very expensive to parallel lines, so we want to make sure that we can pump the most water possible through the existing lines without exceeding the pressure rating of the pipe.
“So what we’ll do is take an AC drive like the Aquavar, which enables us to dial in a pressure that’s safe for the system, and use a pump that’s sized a little bit greater than what the system would normally take with an across-the-line starter. We typically run our pipes at about 75% of the working pressure of the pipe; that’s what we’ve come up with as a safety point.
“So if a customer close to the booster uses additional flow, the drive automatically ramps up to keep that pressure. That enables us to get the most water through our installed pipe without having to parallel lines.”
Lindseth added that by replacing the two 10-hp line-start end suction pumps with the 15-hp SMVT pumps, WEB increased the Dolan station’s flow. Where two pumps were capable of running 160 to 200 gpm, they were now able to run 250 gpm with just one pump. And thanks to their compact design, the pumps take up less room in the station while providing a greater capacity.
Another advantage of the Aquavar controller is the elimination of the control valve. “Because control valves are mechanical devices, we spend a lot of time maintaining them,” Lindseth said. “Every once in a while one will fail; then we either have to go out in the middle of the night to get it unstuck or run the risk of running a tank over.
“But when you put an AC drive in, because it ramps up slowly, you don’t have to deal with the control valve issue. The drive simply ramps up slowly, and there are no pressure spikes. It’s the same thing when the pumps shut off. With the Aquavar controllers, it just ramps down and you don’t need a control valve.”
And when there’s a break in the line, having an Aquavar drive in operation enables WEB to put fewer people out of service. “We can isolate the break while keeping the drive operational at the booster,” Lindseth said. “On the tank side, the customers are fed off of the elevated tank, and on the booster side, the customers are fed off of the AC drive.”
Energy Costs Decrease
Rob Gravatt, project manager for Dakota Pump and Control, the Goulds distributor that supplied the pumps and controllers used for the Dolan upgrade and others that WEB has completed in the past, cites yet another benefit of the Aquavar VFD: reduced energy costs.
“Variable frequency drives eliminate the sudden inrush of electrical current that’s required to start a motor across the line,” Gravatt said. “A rule of thumb is that it takes eight to 10 times full load current to start a motor across the line. So if the motor is rated at 50 amps full load, then its starting current will be 50 x 8, or 400 amps.”
According to Gravatt, the power company will compute the monthly fee based on that inrush of 400 amps, when actual use is just 50 amps 98% of the time. With a VFD, the inrush is eliminated, so the demand is 50 amps rather than 400. That can mean a huge cost savings for the user, even when increasing the horsepower of the motors. Gravatt also cited the protective features of a VFD. “With older, across-the-line systems, the protections were designed to protect the motor.”
For example, Gravatt explained that in a low-voltage situation, the motor will still try to run, but because the voltage isn’t where it’s supposed to be, the motor will draw more current. That extra current is heat, which tends to break down the insulation and shorten the life of the motor. The old way of protecting motors was with thermal overload relays that broke the connection when there was too much heat.
“But VFDs have a processor that calculates things like over voltage, under voltage, or too much current going to the motor. It’s not based on heat, it’s based on a percentage of the current, and if you reach a certain level, it shuts it down. So it’s a great protection feature,” Gravatt said.
According to Lindseth, another nice feature of the Aquavar drives is the ability to link them together. That is especially helpful when supplying bulk users because three of our four pumps can be tied together, so if one pump can’t keep up and the pressure starts to fall off, the pumps will communicate with each other through a data cable, and the second pump will start and pump together. Additionally, if one pump fails, the other one will start automatically, without additional PLCs or other controllers. “You can also program them to alternate,” Lindseth said. “If you don’t have that capability, it can be a problem because one pump will run all the time and the other one will just sit there. Then when the day comes that you need that pump, you may find that it doesn’t work. So the alternation feature is very good.”