Preaction systems are designed to protect water-sensitive areas such as freezers, museums, computer rooms, and clean rooms. These locations contain water-sensitive equipment, precious objects, or are sensitive areas where accidental water discharge is undesirable. Preaction systems may take the place of dry systems.
Preaction systems utilize closed sprinklers, compressed nitrogen or air in the system piping, and water under pressure held below the clapper of the valve. Preaction systems require a detection and release system. When activated by a detector, the valve opens, allowing water to flow into the system pipe and sounding an alarm. When the heat source activates a sprinkler, water flows through only the open sprinklers.