Isolation Valve Impact on Failure Severity and Risk Analysis

The number of isolation valves installed in a water distribution pipe network is typically based on conservative rules of thumb that have been propagated throughout the water industry. However, little work has been done on assessing the valve density’s impact on customer service during pipe failure and repair. This study investigates the impact of valve density on a realistic network’s service metrics. Water distribution network (WDN) service level is quantified using nodal and system severity (ratio of supply to demand during the analysis period) under single pipe failures and customer risk of being out of service (product of likelihood of pipe failure and number of customers out of service). As a baseline for comparison, a WDN is created for a 23.3-km2 (9-mi2) residential area in Tucson, Arizona, following common US design criteria. The impact of the number of valves is assessed for alternative numbers of valves that are placed at random locations. These results are compared with the N and N−1 valving rules. Tradeoffs between system performance and the number of isolation valves are then examined for different network topologies and the levels of connectivity between the transmission and distribution networks.