13.1 INTRODUCTION

Distribution systems of pipelines, pipes, pumps, storage tanks, and the appurtenances such as various types of valves, meters, etc., offer great opportunities for terrorism because they are extensive, relatively unprotected and accessible, and often isolated. The physical destruction of a water distribution system s assets or the disruption of water supply may be more likely than contamination. Loss of water pressure compromises firefighting capabilities and could lead to possible bacterial build-up in the system. Potential for creating a water hammer effect by opening and closing major control valves and or turning pumps on and off too quickly could result in simultaneous main breaks.

Control valves are used to regulate flow or pressure at different points of the system by creating headloss or pressure differential between upstream and downstream sections. The mission of isolation valves is to isolate a portion of the system whenever system repair, inspection or maintenance is required at that segment. The two most common types of isolation valves are gate valves and butterfly valves. Unlike the control valves, little attention has been paid to the layout and operation of isolation valves. Yet, from a reliability point of view, isolation valves are of great interest since they determine the extent of isolation should a portion of the system need to be isolated from the rest of the system. As an extreme example, a system with no valves would have to...