The OPW 178S Series External AST Shut-Off Valve is designed to shut off product flow from an aboveground storage tank, bulk loading rack or any place in the fuel supply line in the event of a fire. The 178S installs in-line on fuel supply piping. A fusible link attached to a spring-operated lever holds the poppet normally open. In the event of a fire, the fusible link melts at 160°F, allowing the spring-actuated poppet to shut off the flow of product in the fuel supply line. The 178S is available in 2″ female NPT connections.