General Description
Double Interlock Preaction Systems are designed for
water-sensitive areas that require the maximum protec-
tion 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 de-
vice 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 releas-
ing control panel, which only then will energize the nor-
mally 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 sys-
tem air pressure as separate zones (inputs) to a
cross-zoned releasing control panel. The solenoid re-
leasing valve remains closed until energized by the re-
leasing 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 pres-
sure 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 again, the Model DDX Deluge Valve will not flow
water due to the cross-zoned control panel configuration.
This requirement for both a detector to operate and the
loss of system air pressure before the Model DDX Deluge
Valve releases water into a preaction system assures
maximum protection against inadvertent water flow be-
fore a sprinkler is open. Double interlock preaction sys-
tems are primarily used to protect refrigerated areas
where accidental water release before a sprinkler is
opened can cause ice blockage, resulting in an inopera-
tive sprinkler system and substantial property damage.
At the heart of Reliable’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 (see Fig.
1). System maintenance is simplified since priming water
is not required and the Deluge Valve can be reset exter-
nally without cover removal. This is accomplished by
pushing in and turning the external reset knob at the rear
of the Deluge Valve (see Fig. 1). This feature provides a
significant system-restoration time advantage
The Reliable Type D Double Interlock Preaction Sys-
tem trim set (see Fig. 2) provides all of the necessary
equipment for connections to the Model DDX Deluge
Valve’s pushrod chamber inlet and outlet ports, the 1
1
4
”
(30mm) main drain, alarm devices, air supply, water sup-
ply, and required pressure gauges. This trim set is avail-
able 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).
Listings & Approvals
Reliable Type D 2” (50mm), 2
1
2
” (65mm), 3" (80mm)
and 76mm Double Interlock Preaction Systems are Fac-
tory Mutual Approved Refrigerated Area Sprinkler Sys-
tems for use in refrigerated rooms or buildings.
Refrigerated area sprinkler systems are FM Approved as
complete systems. Systems are FM approved for use
with thermal detectors and Class A detector wiring only.
Reliable Type D 2” (50mm), 2
1
2
” (65mm), 3" (80mm)
and 76mm Double Interlock Preaction Systems are Listed
by Underwriters Laboratories, Inc. and UL certified for
Canada (cULus) as Special System Water Control Valves
– Double Interlock Type (VLJH) category.
The NYC acceptance number for this system is MEA
258-93-E.
The Reliable Type D Double Interlock Preaction Sys-
tem is UL Listed and FM Approved only when used with
the trim components shown in Fig. 2.
2.
Fig. 1
