The Viking Double SUREFIRE® SIngle Interlock Preaction TRIMPAC® Model D-2 and D-2B used with either a Model E or F deluge valve (A.1), a Viking Easy Riser check valve (F.1), a PAR-3 or VFR400 Release Control Panel (G.1) and all associated trim piping form a unique operating system. The system piping is normally dry and pnuematically pressurized to supervise the integrity of the piping, fitting and sprinklers and provide the failsafe operation of the system upon loss of the primary and secondary power supplies. Double Interlock Preaction systems are commonly used in areas subject to freezing and to help minimize accidential water damage. The Viking SUREFIRE® Double Interlock Preaction TRIMPAC® Model D-2 & D-2B is a factory assembled and tested unit. The enclosure incorporates access doors for the emergency release and alarm test valves and view ports for the prime and water supply pressure gauges.