City of Dover, Del:
By its sheer nature, you expect a sewer bypass project to be messy. Contractors, engineers and pumping solution specialists continue to team to refine bypass sizing, installation, operation and dismantle into swift, efficient segments.
Most stakeholders in a sewer bypass project primarily address sizing in terms of identifying the most efficient pump to meet the required flow and head demands; however, the City of Dover, Del., recently called on Godwin Pumps to also consider meeting those demands with a pumping solution that could fit in the space it had available.
Expecting to dismantle and replace its entire Puncheon Run Pumping Station including the pumps, controls and wiring, the City of Dover needed a solution capable of handling 1,875 gpm at 168 ft of head to 3,000 gpm at 120 ft of head. In addition to these drastically varying flow requirements, the job offered the upfront challenge of limited space availability. With a 30-ft by 30-ft area for pump placement and only slightly more room for system assembly, the lack of space made it difficult to set up the job while leaving enough room for the contractor to move equipment and materials in and out of the building. Added to that was the complexity of identifying pumps that could match the flow requirements and the space restrictions.
“This was not your basic bypass,” said Godwin sales engineer Dale Brackin. “When I looked at the requirements for the job, I brainstormed with [chief engineer] Mike Ramos, [local sales manager] Mike Delzingaro and the contractor, C&D Contractors Inc., of Wilmington, Del.”
The team of Ramos, Delzingaro and Brackin has a combined 50-plus years of experience in the pumping business. They pooled that experience with the technological input of engineer David Heritage to create the winning proposal for C&D Contractors Inc.
“There were so many things to consider, but the starting point remains finding a pump and controls to meet the flow requirements of the system,” said Ramos.
Godwin’s CD160M Dri-Prime pump proved to be the ideal pump to handle the flow and lift required for the project. Available with diesel engines or electric motors, the CD160M pumps are rated for 1,900 gpm and 260 ft of head. For the Puncheon Run Station, Godwin delivered two 150-hp electric drive CD160M pumps with 200-hp variable frequency drives (VFDs) incorporating level transducers and programmable logic controllers (PLCs) to serve as the primary and lag pumps to meet the flow demands. One Critically Silenced 147-hp CD160M diesel pump with a Godwin PrimeGuard Controller and level transducer served as a backup. One standard 147-hp CD160M diesel pump with a PrimeGuard Controller, level transducer and hard-wired Chatter Box Auto Dialer supported the entire system in the event of major storm surges or power outages.
At roughly 11.5 ft long and 4.5 ft wide, the four CD160M pumps were compact enough to meet the space restrictions. However, when combined with all of the other equipment, the job would need and the space available to piece it together, the team quickly met its next challenge.
Along with the CD106M pumps, Godwin determined that the Puncheon Run bypass would require four, 20-ft lengths of 8-in., flanged discharge hose; four 10-in. HDPE dip tubes with 10-in. flanges; and roughly 150 ft of 18-in. HDPE pipe, adapters and elbows that — in addition to check valves, a discharge manifold, combo vents, a flanged reducer and ball valve — all needed to be fabricated and/or assembled onsite in a 30-ft by 30-ft area.
Working with C&D Contractors Inc., Godwin’s team of fusion technicians assembled the HDPE sections and connections in stages, starting from the discharge point (an emergency force main connection), and crane-lifted them over the roughly 20-ft high pumping station building. The team fused the approximately 100-ft length of HDPE discharge pipe, tying it into the single, 18-in. outlet of the discharge manifold. On the inlet side of the manifold, Godwin connected a check valve to each of the four 8-in., 20-ft long discharge hoses that tied directly into each pump.
In the final stages of assembly, the four pumps and their controllers were brought in and connected. When it came to space limitations, the suction point was no exception. The only pickup spot for flow was a large diameter manhole located just before the pump station wet well. The manhole became home to the four 10-in. HDPE dip tubes, four level transducers and left just enough room to install a sewer plug. The entire, assembled system provided adequate space for the contractors to move equipment in and out through the pumping station door.
Working Out the Logic
The VFDs worked only to deliver the flow necessary for system conditions, instead of starting and stopping continuously as with a float-type system. This approach lessens the wear and tear on the pump and decreases the power surges and costs associated with the peak demand on the pump.
Likewise, the level transducers sensed the pressure as the water rose and sent a signal to the VFD to speed up or slow down the motor. The challenge with using a level transducer in a manhole is the turbulence in the water. Godwin inserted a perforated tube into the manhole, creating a stilling well for the transducers. In addition to protecting the transducers from the debris in the manhole, the tube displaced the turbulence, rendering it undetectable. This created a cleaner signal, thereby avoiding rapid cycling. The level transducers were also equipped with a level signal selector switch that took the average of both transducers or would switch from one transducer to another, if a signal went bad.
Pumping on a force main requires a variable head condition that is proportional to flow. When only one pump is running, the discharge head will be much lower than with all three pumps in operation.
Excessive use of a single pump running at full speed with no head could potentially lead to cavitation and needless damage. The VFDs each had a PLC that was programmed to only allow the single pump operation to run up to a lower maximum speed unless more than one pump was required to handle the flow.
The two diesel pumps were each equipped with PrimeGuard Controllers, level transducers. These diesel-driven pumps were required as backups in the Puncheon Run bypass and were controlled independent of the electric pumps, making them self-sufficient. In an effort to exercise the diesel pumps on a routine basis to ensure system functionality for emergency conditions, the first diesel backup (P3) would start up once a week. The system backup pump (P4) would also start once weekly, sending an alarm signal through its Auto Dialer to verify that the backup system functioned properly.
Taking Advantage of the Options
VFDs for electric pumps and PrimeGuard Controllers for diesel pumps opened up a wider variety of capabilities and applications for temporary, portable pumps that had only previously been found in permanent applications. The ability to meet a wider range of flow requirements, including initiating backup pumping; to routinely exercise pumps and/or allow time for scheduled maintenance; and, to send alarm signals enabled reliability and responsiveness: two of Godwin Pumps’ hallmark characteristics.
Using electric-driven pumps as the primary pumps, C&D Contractors only needed to fuel the two diesel backup pumps. In addition, electric pumps combined with VFDs, PLCs and transducers manage the power requirements associated with drastically varying flow levels, decreasing the electricity costs associated with power surges and minimizing the long-term wear on the pumps.
Since the Puncheon Run facility was in a residential area, the electric pumps and Critically Silenced pump needed to operate with minimal noise levels. The combination of electric pumps and Godwin’s Critically Silenced pump unit emitted noise levels no greater than 68 dBA at 30 ft.
Stephanie Morgan is a technical writer for Godwin Pumps, which is headquartered in Bridgeport, N.J. The plan for approaching the flow conditions was simple: The first (lead) electric drive and the second (lag) electric pump were equipped with VFDs that incorporated a level transducer and PLC that allowed the VFDs to work together. Using these controls, Godwin engineers could identify and program system variables that could vary the pump speed to keep up with the influent, start and stop pumps as demand required and alternate lead and lag control between the two pumps to ensure that the entire system was in proper working order and that the pumps experienced an equal amount of run time/wear exposure to prolong performance.