The Double Interlock Preaction System with Electric/ Electric Release is generally used to protect water sensitive areas such as computer rooms, storage areas, refrigerated areas etc., to avoid water damage due to inadvertent flooding of the sprinkler system piping.
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.
This system utilizes a Deluge Valve and Riser Check Valve. The Riser Check Valve isolates the Deluge Valve from the system air pressure. Riser Check Valve provides an air check so that the system can be automatically pressurized with a nominal supervisory air or nitrogen pressure of 10 psi (0.69 bar). A supervisory low pressure alarm switch can be set at nominally 6 psi (0.42 bar), on decreasing pressure, to indicate whether there are any abnormal leaks in the sprinkler system piping. Loss of air pressure from the system due to accidental leakage will not cause Deluge Valve to open.
The releasing trim for the Deluge Valve utilizes a Solenoid Valve that is energized with cross-zone releasing circuit of release panel. The system air pressure holds the Dry Plot Actuator closed, whereas the Solenoid Valve remains closed until it is electrically energized by a Deluge Valve Releasing Panel (automatic control unit). The Releasing Panel is operated by either a fire detection device or manual electric pull station.
In order for the Double Interlock Pre-action System to automatically actuate, two independent events must occur. Zone 1 of the Releasing Panel must operate upon automatic operation of the electric fire detection initiating circuit or operation of the electric-manual pull initiating circuit, and Zone 2 of the Releasing Panel must operate via the Low Air Pressure Alarm Switch upon loss of air pressure from the sprinkler system piping, due to operation of one or more sprinklers. The Double Interlock Preaction System will automatically actuate only when both Zone 1 and Zone 2 of the Releasing Panel have operated, energizing the Solenoid Valve.