Abstract: A device for turning a valve stem or the like between two positions in response to earthquake forces or other shock forces, and including a member which is spring urged rotatively in a predetermined direction relative to a body structure and which has a lost motion connection with the valve stem or other element to be turned in order to enable initial movement of the member by the spring to develop momentum before applying force to the stem, a latch element releasably retaining the member against spring induced movement, and inertia actuated weight means responsive to shock forces to release the latch element and permit movement of the member to turn the valve stem.