The valves are intended to be mounted in the gas line upstream or downstream of the gas-line pressure regulator and gas meter outside the structure. These valves do not replace the manual upstream shut-off valves provided in the gas service line. Our valve consists of a swing check valve arrangement with an acceleration-sensitive triggering mechanism. The trip mechanism consists of a steel ball resting on a tapered cup-shaped support. The horizontal motion of an earthquake causes the ball to move from the center of the support.This allows the balls mass to act upon the movable pipe of the trip mechanism, activating the valve and initiating closure. Springs assist the valve- flapper to close and gas pressure assists in holding the valve disc in the closed position. The trip mechanism is factory set and sealed. A sight glass is provided so that the Open or Closed indicator can be seen and the trip mechanism status of the valve can be easily determined.