Abstract: A mechanical leak arresting valve is disclosed in which fluid through the valve is limited to a range between a predetermined minimum flow rate and a predetermined maximum flow rate, and where both a small or large downstream leak mechanically causes the valve to lock closed. The present invention uses a locking mechanism triggered by a pressure differential resulting from the downstream leak to block the flow of fluid through the valve until the fluid source upstream is stopped. Reduction of the upstream pressure by the stopping of the fluid source automatically resets the valve without further manipulation.