The Town of Leesburg, VA had been dealing with a problem with a set of progressive cavity pumps at their water treatment plant since shortly after the pumps were installed in 2009. The Netzsch NEMO pumps were originally supplied and installed as part of a plant expansion by an out-of-state general contractor and distributor. Town representatives contacted Wood Equipment Company (WEC), the Virginia distributor of Netzsch pumps, in the early spring of 2021 for assistance. They described the problem to the WEC Territory Sales Manager as follows: When the pumps are called to run, the rotors will not begin turning without forced mechanical assistance by Town maintenance personnel.
For background, these Netzsch Progressive Cavity Pumps are pumping sludge off the bottom of a pair of settling tanks. Typically, the pumps are automatically called to run once per hour for 5 to 10 minutes. However, when they received the run command, the pumps’ metal rotor and rubber stator would appear to be bound together and unable to turn freely. The Town’s personnel would have to use a large pipe wrench to break the two components free from one another in order for the pump to run. After stopping, the pump would again seize up and be unable to run automatically. As you can imagine, this labor-intensive and time consuming process became a major issue for water plant personnel. The Town needed to find a permanent solution.
In response, WEC Territory Sales Manager Brent Yager made several trips to the facility to help the Town troubleshoot the pumps. Brent did not believe that the pumps themselves were the problem, as Netzsch pumps are known for their quality and reliability. Alternatively, Brent believed that there was a system design flaw that was not allowing the pumps to operate as intended. As such, Brent first tried adjusting the run parameters in the existing Siemens Variable Frequency Drives (VFDs). This did not correct this issue, so it was theorized that the Siemens VFDs were slightly undersized for the application. Progressive Cavity pumps have an interference fit between the rotor and stator, which requires a large amount of torque to initially start the pump. The motor on the pump was 7.5HP, and the Siemens VFD was also 7.5HP Heavy Duty. The Town agreed that the VFDs were undersized, and opted to replace the Siemens VFD with a pair of Schneider Electric, Altivar 660 series VFDs in 10HP Heavy Duty. After the new VFDs were installed, Brent returned to the facility to continue troubleshooting, but unfortunately the new VFD was still not able to start the pump.
Brent then contacted Netzsch’s excellent tech support team to help with the problem. Netzsch gladly sent a new Stator and two of their management team down to help troubleshoot the pumps. On top of that, they also supplied a larger 10HP motor to provide more starting torque. Once the parts were installed, the team tried again, but the pump still would not run on its own. The team was surprised, but undeterred.
Brent continued working on the problem, believing the solution lie within the VFD settings. As Wood Equipment Co. had recently entered into an agreement with Schneider Electric to become an OEM Distributor, Brent brought Schneider’s Technical Support team into the loop, and they created an action plan. Schneider’s tech support gave Brent recommendations for adjusting several advanced settings within the VFD to hopefully make the pumps run as designed. Brent returned to the Town with one of the Schneider representatives to assist. They were able to make the suggested adjustments quickly, and sent the run command. The drive engaged the pump motor and it ran perfectly. Success!! Several starts and stops were made on the pump to ensure it operated correctly. After more than 10 years, the problem that had plagued the Town of Leesburg’s Water Treatment Plant was finally solved.
Wood Equipment and Brent Yager would like to thank Jeff Bye and Brian Polkowski with Netzsch Pumps, as well as Robert Burks, Mike Caccia, and Scott Simpson with Schneider Electric for their assistance. We also thank the great staff working at the Town of Leesburg’s Water Treatment Plant for their assistance and patience. A team effort was required to fix this long-standing problem, and together we were able to make it happen!
If you have troublesome applications, new design requests, or any pumping needs, please feel free to reach out to Wood Equipment Company for help at 804-798-8844, or request a quote online at www.woodequip.com.