The City of Columbus, OH
Among the most interesting components of the OARS project is a 215-foot deep, 60-mgd capacity pumping system and a 185-foot deep screening system. The OARS pumping system consists of multiple pumps that can handle enough flow to dewater the tunnel within two days of a large flow event. The difficulty with the deep pumping system on this project is that the static head condition varies from as much as 210 feet when the tunnel is empty to as little as 15 feet when the tunnel and shafts are full.
The response to this pumping challenge was the installation of four Flygt Model CP3351.995, 800-hp, 4160-volt, 15-mgd adjustable speed pumps that handle the majority of the work at the deep tunnel level, and two Flygt Model CP3531.960, 450-hp, 4160-volt, 20-mgd adjustable speed pumps to handle the shaft dewatering. Two grit pumps, Flygt Model NP3301.095, 105-hp, 460-volt, and one Flygt Model NP3306.715, 100-hp, 460-volt were also installed.