DOUBLE INTERLOCK PREACTION

A Double-Interlock Preaction System is a fire protection system designed to provide the highest level of protection against accidental water discharge while ensuring dependable fire suppression. In this configuration, the preaction valve opens only when two independent events occur—operation of a detection system and activation of one or more sprinklers. The system piping remains dry until both conditions are met, preventing water from entering the sprinkler network unless a true fire is verified.

Two common actuation methods are used. The Electric/Pneumatic trim employs an electric detection system to open an intermediate valve (electric solenoid) on the preaction valve trim. The operation of a sprinkler vents pneumatic pressure from the system piping; the drop in air pressure allows a Pneumatic Actuator (Dry Pilot Actuator) on the valve trim to open, venting pressure from the valves pressure chamber and opening the main preaction valve. The Electric/Electric trim uses two separate electrical signals—one from the detection system and another from a sprinkler pressure switch or pressure device—to open the valve.

Double-interlock systems are typically used in environments where accidental water discharge could cause severe damage, such as cold storage freezers, data centers, archives, and museums. Their dual-verification requirement minimizes false activation while ensuring water is promptly delivered when both fire conditions and sprinkler operation confirm a genuine emergency.