January 2011 Vol. 66 No. 1
Features
Bypass Pumping Details Often Taken For Granted
Addressing the problems of the nation’s aging underground infrastructure is a priority for many cities and sanitary sewer and water districts across North America. Though slowed by the economy, there is still a host of massive rehabilitation and construction projects under way or in planning stages with many more such efforts to come.
A critical component of rehabilitation projects is the design and construction of efficient temporary by-pass pipeline systems to divert flow from segments of pipe being rehabilitated or replaced so that vital services to residences and businesses are not interrupted during construction.
For projects containing large-diameter pipes, the bypass system itself is a major project.
“Depending on the nature and scope of the project, bypass pumping can be relatively easy or extremely difficult and complicated,” said Lynn Osborn, senior applications manager for Insituform Technologies, a leading worldwide provider of proprietary technologies and services for rehabilitating sewer, water, energy and other industrial pipelines.
“For small sewers, the flow is often plugged or handled with one small pump,” Osborn continued. “As pipe diameters and flow rates increase, bypass pumping can become one of the most complex and costly components of the project, especially when flows can exceed 100 million gallons per day.
“However, the importance of bypass pumping is always critical because sewage overflows or spills, large or small, can cause significant project consequences, social impact and/or environmental damage.”
Bypass systems are installed by general contractors or specialist subcontractors.
The heart of a bypass system is a pump or pumps, and several pump companies have developed equipment to satisfy the demands of bypass installations. Some manufacturers and/or their distributors serve as subcontractors providing pumps and other equipment on a rental basis, installing the bypass system and removing it after the project is complete.
What’s best for the customer
Godwin Pumps rents pumps and provides bypass design and installation services.
“We will do whatever is best for the customer,” said Ron Askin, vice president and director of sales. “We rent a lot of equipment set up by the contractor, but it seems like more and more are requiring turnkey systems. In that case, we engineer the solution, rent the equipment including pumps, pipes/hoses, fittings, fuel tanks, road ramps, motor controls, level floats, etc. In addition, we provide pipe fusion services, pump watch and pump maintenance services.
“Temporary bypassing is what we do day-in and day-out. We have experience with a broad range of systems that have already been designed and successfully applied, and we modify those to fit the specific project. It is important not to reinvent what’s already proven technology, so we encourage new engineers to spend time reviewing available installation designs. New engineers benefits from our collective experience, and we benefit from their fresh insight. It is different than designing a permanent structure, so collaboration is critical.”
Askin said when a subcontractor is employed, typically the subcontractor is given the suction point, discharge point and a required flow and with that information the bypass subcontractor designs the system.
Understanding flow is the key to designing a bypass system, Askin believes.
“In addition,” he said, “because end suction centrifugals are affected by suction lift, this needs to be taken into account. When a system isn’t performing to the published curve, it is typically a suction lift issue. We help a lot of owners out after they have had a system installed by a company that didn’t understand this principle.”
Most common problems during the design process, Askin continued, “is not understanding flows and the redundancy.
“If a temporary system is required to handle 1.5 times the peak wet-weather flow and 100 percent redundancy,” he explained, “the system is impractically large. The difference between engineering a system and simply renting a pump to meet flow requirements is that an engineered system provides the exact equipment needed to efficiently meet system demands and potential overburdening without specifying over- or under-powered equipment.”
Noise control has become key in these systems, said Askin. Attenuated units with noise deadening insulation and hospital-grade mufflers to reduce the pump noise are used in areas where noise is an issue. These models are increasingly popular, particularly in residential applications, he added.
Turnkey
“Thompson Pump is a full-service pump company that designs and installs complete bypass pumping systems,” said Kirsten Petersen Stroud, marketing manager. “We have a comprehensive applied products division and numerous bypass specialists. From beginning to end, we provide everything from calculations, set-up, installation, HDPE pipe assembly, on-site support, pump watch, maintenance and tear down. We provide turnkey projects utilizing our years of expert experience and knowledge.”
Stroud said general contractors that specifically focus on water and wastewater often are more successful with bypasses than basic general contractors.
“Understandably,” Stroud said, “when the economy started declining, we noticed a trend for general contractors without extensive bypass experience bidding on this specialized work in order to augment their income. Many contractors without fundamental bypass experience have required more guidance and product training or have subcontracted the job to get it performed properly.
Stroud said there are several essential steps necessary to complete a successful bypass, and a specialist in design, estimation and set up always should be involved. Factors to consider in planning include, but are not limited to, source of flow, average flow and peak flow potential, properties of the influent and the discharge point.
Essential elements of a bypass system include pumps, sizes and types of piping and fittings, check and gate valves and controls.
“Some pump users do not thoroughly understand the efficiency portions of a standard pump curve and the importance of sizing a pump for maximum efficiency,” said Stroud. “Having a pump that does not exactly meet job requirements may work for some applications, but this is not the case for sewage bypass systems. The appropriate pump must be precisely defined, and this is accomplished by examining the pump’s curve — the total head developed by the pump at various flows.”
Bypass contractors
BakerCorp, with worldwide operations that include bypass pumping and excavation shoring, provides turnkey bypass system services.
“Generally, bypass requirements are specified by the owner, usually a municipality,” said Chuck Rickman, vice president of product development. “The details of how that is accomplished are usually left up to the bypass subcontractor such as BakerCorp. We provide pumps (including sound attenuated models), hose, fittings, setup, pump watches when required, berms, generators for electric driven pumps, day tanks, remote monitoring capabilities, TDH calculations and process flow diagrams.”
Rickman said to plan and design a bypass system it is essential to know normal and peak flow rates, amount of suction lift, distances the sewage must be pumped, and elevation changes. Are there noise restrictions that dictate the use of sound attenuated diesel driven pumps, or are electric driven pumps required? Are there space limitations that would restrict the size of pumps or how piping is run from manhole to manhole?
“This information is critical because you don’t want to design a system based on what you think you know as true only to find out later that some critical piece of information was incorrect that can completely invalidate the design. If a mistake is discovered early enough, it can be remedied before physical preparations are started, with the worst consequence being a change in the subcontractor’s bid. For instance, if peak flows are far higher than expected, there is the risk of surcharging or overflows, and that, of course, is a disaster.”
BakerCorp had more than 90 locations nationwide and international operations in Europe, Canada and Mexico. In addition to the utility market, BakerCorp provides integrated services for general construction, oil and gas, industrial services, environmental remediation, and many other markets.
FOR MORE INFO:
Godwin Pumps, (856) 467-3636, www.godwinpumps.com
BakerCorp., 800-BAKER 12, www.bakercorp.com
Thompson Pumps, 800-767-7310, www.thompsonpumps.com
Rain-For-Rent, 800-742-7246 , www.rainforrent.com
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