DDX Type D Double Interlock Preaction System

Double Interlock Preaction Systems are designed for water sensitive areas that require the maximum protection from inadvertent water flow into the sprinkler system piping. A refrigerated area is an example of this type of water sensitive environment.

To flow water into a Type D Double Interlock Preaction System, two events must take place. A fire detection device must operate, and the low air pressure switch must be operated by the loss of system air pressure (sprinkler operation). These two signals must coexist at the releasing control panel, which only then will energize the normally closed solenoid valve (175 psi (12,1 bar) or 250 psi (17,2 bar) rated), causing water flow into the system. These Systems utilize fire detection devices and system air pressure as separate zones (inputs) to a cross-zoned releasing control panel. The solenoid releasing valve remains closed until energized by the releasing control panel. This will occur only when both a fire detection device is operated and the low air pressure switch has detected sufficient loss of system air pressure (sprinkler operation).

In the event that the system piping is ruptured, or a sprinkler head is accidentally opened, the low air pressure switch will operate and an alarm will sound. The Model DDX Deluge Valve, however, will not be released to flow water since the solenoid valve remains closed due to the cross-zoned control panel configuration. The same end result would occur if a fire detection device were falsely operated. The control panel will activate an alarm, however, the Model DDX Deluge Valve will not flow water due to the cross-zoned control panel configuration. The requirement for both a detector to operate and the loss of system air pressure before the Model DDX Deluge Valve releases water into a pre-action system, assures maximum protection against inadvertent water flow before a sprinkler is open.

Double interlock preaction systems are primarily used to protect refrigerated areas where accidental water release before a sprinkler is opened can cause ice blockage, resulting in an inoperative sprinkler system and substantial property damage. At the heart of Rapidrop’s Type D Double Interlock Preaction System is the Model DDX Deluge Valve. This Deluge Valve is a hydraulically operated, straight-through-design, differential type valve.

System maintenance is simplified since priming water is not required and the Deluge Valve can be reset externally, without cover removal. This is accomplished by pushing in and turning the external reset knob at the rear of the Deluge Valve. This feature provides a significant system restoration time advantage. 

The Rapidrop Type D Double Interlock Preaction System trim set provides all of the necessary equipment for connections to the Model DDX Deluge Valve’s pushrod chamber inlet and outlet ports, the 1 %” (30mm) main drain, alarm devices, air supply, water supply, and required pressure gauges. This trim set is available in individual parts, in time-saving, segmentally assembled kit forms, or fully assembled to the Model DDX Deluge Valve (with or without a control valve).