Apr 12, 2006

Pumps Play Critical Role in Bypass Project

Recently, White Contracting earned one of its largest contracts to date in Memphis, Tenn., a project that required a sewer bypass system. The company installed several thousand feet of new 72-in.-diameter gravity flow sewer pipe.

The final step of the project was to connect the new pipe to the existing sewer system. A temporary sewer bypass system was needed to divert the existing 54-in. sewer line, which required a minimum capacity of 35 million gal of sewage per day and even more during peak flows. Limited space required the number of pumps used for the bypass to be at a minimum.

White Contracting, a long-time customer of Thompson Pump’s Mississippi branch, asked Jim Templeton, Thompson Pump sales representative, to review the application to see if the company’s products would work for the bypass.

Project specifications

Templeton proposed using four 16-in. compressor-assisted solids handling high-pressure pumps, each capable of a maximum of 11,000 gpm, and two 12-in. compressor-assisted solids handling high-pressure pumps, each capable of a maximum 8,500 gpm. The pump manufacturer also proposed using 18-in. high-density polyethylene (HDPE) pipe, which was more capable of handling the large amount of sewage.

Each pump would be fitted with 18-in. flanges to couple the HDPE pipe directly with the pump’s suction ports. All of the 16-in. pumps and one of the 12-in. pumps would be used for the primary pumping. The remaining 12-in. pump was for backup purposes.

To better direct the five different discharge lines, Thompson Pump also proposed using a manifold with five inlets and two outlets. The HDPE pipe from the outlet ports of the manifold would run approximately 750 ft away from the pumping area to the desired manhole that would accept the discharge. The manifold’s inlet ports would each have a gate valve in order to isolate each pump—allowing pumps to be disengaged from the system at any time without upsetting the system.

Thompson Pump was awarded the contract and immediately sent a team from their Mississippi branch to begin fusing the HDPE pipe system together and positioning the pumps and manifold.

The ultimate test

The bypass system was positioned one manhole upstream of the tie-in site, where the 72-in. line was to be connected to the 54-in. line, and discharged into a manhole on a previously installed section of the new 72-in. line downstream of the tie-in site. The bypass system was installed quickly and began operating efficiently. Within a matter of days, however, the Thompson Pump bypass system would be put to the ultimate test.

Hurricane Ivan was threatening the Gulf Coast, so local residents evacuated the beachside areas and low-lying regions, heading north to escape the storm. Hotels in Memphis were quickly booked to capacity as evacuees flooded into town. This caused millions of gallons of excess sewage to enter the sewer system Thompson Pump was bypassing. Because the system design allowed for additional capacity, the bypass was capable of handling the additional sewage and continued to operate efficiently even as the hurricane made landfall.

“We did notice the flows increase, but [the pumps] didn’t have any problems keeping up,” Templeton said. “There were no mechanical failures; no sewage spillage; and never a problem maintaining flows.”

All of the pumps used for this project were equipped with Thompson Pump’s exclusive Enviroprime priming system, used to prevent blow-by from discharging onto the ground. The priming system also extends the life of the pump by separating air and water, keeping the venturi from clogging.

Clayton Webb, project manager for White Contracting, was pleased with the positive outcome of this bypass job.

“It’s unusual; this is the largest sewer bypass we have ever done, and it’s also the most trouble-free sewer bypass we have ever done,” Webb said.

About the author

Majid Tavakoli is vice president of applied products for Thompson Pump and Mfg. Co., Inc. He can he reached at 386/944-4105 or by e-mail at [email protected].