Long-distance water-supply project is an effective way to solve the uneven spatial and temporal distribution of water resources, but the safety of water conveyance system is threatened seriously by water-hammer. Based on the research of the characteristic of water-hammer with pipe friction considered, the formula of indirect water-hammer is deduced and the application scope of the formula is also discussed, which is the theoretical basis for the design of polyline closure law. To the defects that valve closure time is long and response of accident is slow in the long-distance water-supply project, polyline closure law is designed with consideration of valve overflowing property, which greatly reduces the closure time and water-hammer. At the same time, the flow inertia is large in long-distance water-supply project and break point of polyline closure law is hard to fix. In order to improve the reliability of the mechanical operating system, locking device is installed, which make the polyline closure law carry out successfully and provide a new idea for water hammer protection in long-distance water-supply project.

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