The Double Interlock Preaction System with Electric/Pneumatic 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 conditions, the 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 is the most commonly used system. This system utilizes a Deluge Valve Fig.502 and Riser Check Valve Model CH. The Riser Check Valve isolates the Deluge Valve from the system air pressure. The Riser Check Valve provides an air check so that the system can be automatically pressurized with a supervisory air or nitrogen pressure of 42 PSI (2.94 Bar). A supervisory low-pressure alarm switch can be set at 20 PSI (1.40 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 the Deluge Valve to open.
The releasing trim for Deluge Valve utilizes a Solenoid Valve and a Dry Pilot Actuator in a series configuration. The system air pressure holds the Dry Pilot 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 either by a fire detection device or a manual electric pull station. In order for the Double Interlock Pre-Action System to automatically actuate, two independent events must occur.