The Single Interlock Supervised Preaction System is generally used to protect water sensitive areas such as computer rooms, storage areas, libraries, archives, banks, etc., to avoid water damage due to damaged sprinklers or damaged sprinkler piping. Preaction System is also effectively used to have Pre-alarm of a possible fire condition and allows time to extinguish fire by hand held fire extinguishing equipment, prior to water discharge through sprinkler heads. It uses an automatic sprinkler with supplemental detection system. In the event when fire cannot be extinguished by hand held fire extinguishing equipment, the increase in temperature will open one or more sprinkler heads to discharge water.
In normal condition, preaction system does not contain water in the sprinkler piping. The sprinkler piping contains air pressure for the purpose of supervising its leak tightness. As per NFPA, the preaction system employing more than 20 automatic sprinklers is to have the sprinkler piping automatically supervised.
The electric detection system in single interlock preaction system will respond to a fire faster than the automatic sprinkler. When fire is detected through electric system, the primary water control deluge valve opens, allowing water flow into the sprinkler piping in readiness for possible subsequent opening of one or more sprinklers.