PREACTION AUTOMATIC SPRINKLER SYSTEM The FIREFLEX® DUAL system integrates a Viking preaction sprinkler system with the Model F1 Straight Through Deluge Valve. FIREFLEX® DUAL systems are provided with an integrated 2” or 3” diameter single or double interlocked preaction system. SHUT-OFF VALVE OPTION The riser shut-off valve option consists of Viking Valves & Systems. EasyPac® Riser Assemblies; Wet Pipe Systems; Dry Pipe Systems; Deluge & Preaction Systems; ... Deluge & Preaction Systems : Single Interlock ... Pre-action fire sprinkler systems employ the basic concept of a dry pipe system in that water is not normally contained within the pipes. The difference, however, is that water is held from piping by an electrically operated valve, known as a pre-action valve.