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Seismically actuated gas shutoff valves offer protection in the event of an earthquake by blocking the flow of gas. Commonly referred to as seismic valves or earthquake valves, these valves contain sensing mechanisms which cause the valve to positively shutoff the flow of gas upon detecting a given peak acceleration over a period of time. Gas flow is shutoff by blocking the flowpath of the gas either through the use of a ball or a door / flapper. Miners & Pisani offers only the door/flapper type because of its inherent superiority of design. While these valves still use a rolling ball for their sensing mechanism, a door is used to block the gas flow. The door is secured in place by the upstream pressure of the gas along with a spring or magnet. This ensures the valve will not re-open regardless of the valve position which might move as a result of falling objects and twisted pipe, among other things. These valves can only be reset manually which allows for careful inspection of the gas system prior to reset. Automatic reset mechanisms are not recommended as they may not be sensitive enough to detect a slow gas leak.