a gas flow isolation device includes a gas flow isolation valve movable from an opened condition to a closed condition . the module isolation valve in one embodiment includes a rupture disk in flow communication with a flow of gas when the module isolation valve is in an opened condition . the rupture disk ruptures when a predetermined pressure differential occurs across it causing the isolation valve to close . in one embodiment the valve is mechanically linked to the rupture disk to maintain the valve in an opened condition when the rupture disk is intact , and which permits the valve to move into a closed condition when the rupture disk ruptures . in another embodiment a crushable member maintains the valve in an open condition , and the flow of gas passed the valve upon rupturing of the rupture disk compresses the crushable member to close the isolation valve .