A sewer bypass pumping system was needed to allow for the installation and upgrade of the Plott Road Pump Station, owned by Charlotte-Mecklenburg Utilities of Charlotte, N.C., which began last July and was successfully completed in three months.
The original pump station consisted of a wet well and a dry-pit pump with connecting pipes. The pumping station regularly flooded during storms and the old pumps were in need of replacement. The project entailed demolishing the existing dry pump and converting the existing wet well to a submersible pumping station. Hall Contracting was awarded the rehabilitation project.
Having worked with the engineer, Arcadis, on the job specifications, Godwin Pumps was called on to do the bypass pumping.
Pump specialists from Godwin’s local Charlotte rental office designed, assembled and supported a sewer bypass pumping system to handle 2,100 gpm of wastewater at 220 ft of total dynamic head to meet the requirements for the job.
Due to the duration of the job and a confined site, fused high-density polyethylene was used for the discharge pipe to make for a very reliable, tight system. The pumping system included a primary HL6M high head model Godwin Dri-Prime pump with an electric motor and one backup diesel high head Dri-Prime pump.
The pumps used in this application are automatic self-priming pumps designed with an oil bath mechanical seal that enables the units to run dry indefinitely without damage—a benefit in intermittent flow conditions common in sewer bypass pumping. The pumps automatically prime and reprime to 28 ft of static suction lift and are constructed with a cast chromium steel impeller for longer life to handle raw sewage, sludge, oil and stormwater.
Because power was readily available, the decision was made to use an electric drive primary pump versus a diesel unit.
An electric drive pump raised new issues to resolve. Operated by float switches, the electric drive pump could potentially place an extra demand on the power supply system at each startup. Therefore, Godwin utilized a reduced voltage, soft start motor controller on the job. A soft start controller slows down the demand on starting amps of the motor drive pump, reducing the immediate load on the power supply and avoiding a potential shutdown.
Although the contractor had personnel onsite monitoring the bypass system 24 hours a day, the job specifications required that the system also be connected to telemetry for increased reliability. If the backup diesel pump were to be activated, an auto dialer would alert the contractor, Godwin and the Charlotte-Mecklenburg Utilities Department, so that appropriate measures could be taken if necessary.
“What’s unique about this system is the combination of the Godwin Dri-Prime pump and its ability to automatically prime and a discharge piping system which automatically releases trapped air allowing the pump to come online smoothly and reliably,” said a Godwin representative. “In this system, there is no danger of an air lock interfering with the pump’s ability to get online.”
In addition, the contractor performed a tap on the force main and provided a flange to connect to the temporary bypass system’s discharge line. Godwin installed a check valve on this flange and a combination air-vacuum release vent between this valve and the primary pump.