AWWA JAW60845

Negative pressures have been documented in a variety of distribution systems as a result of either unintentional (e.g., power outages) or intentional (e.g., pump stoppage or startup tests) circumstances. The production of transient low and negative pressures in otherwise pressurized potable water supply distribution systems creates the opportunity for contaminated water to enter the distribution system from external environments. However, few systematic or long-term studies have monitored real distribution systems for the occurrences of transient low and negative pressures under field conditions. A comprehensive and lengthy study was conducted to monitor the occurrence of low- and negative-pressure transients and to evaluate the effect of a variety of operational situations on the development of these events. The authors also compared the efficacy of electronic and mechanical pressure-monitoring devices for detecting transient pressure surges. Because of the danger of contamination, the water supply profession should be aware of the occurrence and potential adverse effects of transient low and negative pressures. Water providers can use the information in the article to aid in the design of a pressure-monitoring program to help determine their systems' susceptibility to low and negative pressures. Such a program could use hydraulic surge models to assess the potential for pressure transients to occur throughout the system under a variety of operating conditions. Study results also point to the usefulness of high-speed electronic pressure monitors for detecting surge events. Includes 12 references, tables, figures.