Abstract: A seismic event shut-off gas valve having a primary conduit arranged for orientation in a vertical position, and a secondary conduit intersecting the primary conduit at an intersection, with a plug member slidably secured in the secondary conduit in a first position and slidable to a second position, wherein the plug member is arranged to engage a sealing ring within the primary conduit upon dislodgement of the plug member from the first position by a seismic event. A chain member secured to the cap and the plug member permits the cap member to be removed from the secondary conduit to withdraw the plug member from the second position to the first position and reposition the plug member in the secondary conduit to the first position.