safety valve The closing body is held in the back position by a fuse, and the gas is able to flow. If the fusible cut out melts, e.g. because of fire, the fuse body is pushed forwards by the spring, and the gas flow is interrupted. description ordernumber 380 see also: pressure-reducing valve fuel oil hold-back system Procon-ten safety system (Audi) backflow preventer (EA 1)