Protecting Water Systems from Transient Pressures: Davidson Water, NC Case Study

Last Modified: Oct 02, 2018

Authors:

  • Crystal Broadbent PE - Hazen and Sawyer
  • Robert Walters - Davidson Water Inc.

This presentation will illustrate the importance of performing a surge analysis on booster pump stations for the protection of water distribution systems.

Davidson Water, Inc (DWI) owns and operates approximately 21 booster pump stations supplying 12 pressure zones. Most of the pipe system was installed in late 60’s and early 70’s, and approximate 70% of the system is PVC pipe. DWI has experienced multiple pipe breaks on PVC pipes and suspected that pressure surges were causing the breaks. PVC pipe is adversely affected by cyclic pressure changes and has a lower maximum surge allowance than ductile iron pipe.

The largest booster station is Hyattown Pump Station (Hyattown) which supplies two pressures zones, serving nearly 70% of Davidson Water’s customers. Recent maser planning efforts concluded that future customer demand will exceed Hyattown’s pumping capacity within the coming decade. The station was also nearing the end of its useful life. DWI evaluated various upgrade alternatives and decided to construct a new pumping station.

The pump station design included a surge analysis, which determined that surge tanks were needed to protect the pumps and distribution system.

The surge analysis evaluated power failure for two sets of pumps, since the pump station supplies two pressure zones. The surge model showed that pressures within the distribution system fell to full vacuum conditions and subsequent pressure spikes reached as high as 350 psi. Surge tanks were recommended to mitigate the vacuum conditions and subsequent high pressures.

During a redesign of a second booster station, Hargrave Pump Station, a surge analysis showed a bypass check-valve was sufficient to mitigate transients. This solution was far less expensive than a surge tank.

This presentation will benefit, modelers, pump station designers and distribution system operators.

For more information, please contact the author at cbroadbent@hazenandsawyer.com.

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