SINGLE INTERLOCK PREACTION

A Single-Interlock Preaction System is a fire protection system designed to prevent accidental water discharge while ensuring rapid sprinkler operation when fire conditions are confirmed. The system employs a preaction valve that remains closed until a detection event occurs. Common actuation methods include electric actuation, where a solenoid valve mounted on the valve trim opens upon signal from an approved detection system to a releasing panel; dry pilot actuation, which uses small-diameter dry pilot piping with pilot sprinklers or pneumatic detectors connected to a dry pilot actuator; and wet pilot actuation, where wet pilot lines with thermal-responsive sprinklers detect heat to trigger the preaction valve. Once actuated, the main valve admits water into the sprinkler piping. The water only discharges from sprinklers after sprinklers have activated. The integrity of the system’s dry piping is typically supervised by maintaining air or nitrogen pressure within the piping, monitored by a low-air-pressure switch that signals any loss of pressure. This ensures early detection of leaks or mechanical damage and maintains system readiness while minimizing the risk of unwanted water discharge before confirmed fire detection.