Abstract: There is shown and described a shock actuated, shut-off valve for fluid flow lines which includes a valve housing having an inlet conduit, an outlet conduit and a central chamber which communicates between the inlet and outlet conduits. A channel is provided around the interior of the valve above the central chamber. A ball normally rests in the channel. The central chamber is adapted to selectively receive the ball from the channel in a position between the inlet and outlet conduits thereby to selectively interrrupt fluid flow through the valve. A reseating mechanism is provided at the bottom of the valve wherein the ball can be selectively removed from the closure position and returned to the channel.