Dry Pilot Single Interlock Preaction Systems are used in
areas that may be subjected to freezing conditions. They can
also be utilized to obtain installed sprinkler heights and pipe
lengths greater than the allowed for wet pilot systems. A dry
pilot line installation consists of an air-pressurized line of closed
sprinklers or pilot line detectors (Reliable Model F1-FTR), which
are located in the area to be protected. NFPA 72 or the Author-
ity Having Jurisdiction (AHJ) should be consulted for spacing
and elevation requirements for the installation of dry pilot sprin-
klers/detectors.
To maintain the Model DDX Deluge Valve in a closed posi-
tion: in areas where moisture-laden air could cause a freezing
condition, or other problems in the dry pilot line, the use of a dry,
compressed gas such as nitrogen is suggested. Approved gas
handling regulators (see Reliable Bulletin 254) and connections
are recommended.
The re sprinkler system piping is generally supervised (see
NFPA 13) with air pressure. Loss of supervisory air due to a
damaged sprinkler or the sprinkler piping will not cause the
Model DDX Deluge Valve to open. A check valve in the trim
prevents pneumatic pressure from escaping the Model LP Dry
Pilot Actuator in this event. A low air pressure switch (Potter
PS25-2) is also provided in the trim. The contacts of this switch
will close on the loss of air in the sprinkler piping, thereby provid-
ing a low air alarm to aid in insuring the integrity of the sprinkler
system piping. The pressure switch should be wired to a super-
visory alarm bell or the building alarm system.
Damage to a dry pilot line sprinkler/detector or the dry pilot
line piping that causes a signicant loss of pressure will cause
the Model DDX Deluge Valve to open, flowing water into the re
sprinkler system piping. The supervisory air supply for both the
dry pilot line and the re sprinkler piping can effectively be main-
tained by means of pressure-switch-operated, tank-mounted
air compressor and a Reliable Model A Pressure Maintenance
Device (see Reliable Bulletins 251). The compressor tank pro-
vides a reserve supply of air, and the Model A Pressure Mainte-
nance Device consistently regulates the air pressure of both the
dry pilot line and the re sprinkler piping.
The dry pilot line sprinklers/detectors must be more sensitive
to the heat from a re than the sprinklers in the re sprinkler
system. The Model F1-FTR (Fixed Temperature Release) is
specically designed for use in dry pilot line operated sprinkler
systems. Dry pilot line sprinklers are detection devices and do
not provide any water to aid in the reghting capability of the
re sprinkler system.
The dry pilot line is connected to the Model LP Dry Pilot Ac-
tuator and is held closed with between 8 and 28 psi (0,6 and
1.9 bar) of pneumatic pressure. To fully operate a dry pilot line
preaction system, heat from a re must fuse a dry pilot line de-
tector thereby releasing the air pressure from the Model LP Dry
Pilot Actuator. The water pressure is then able to overcome the
pressure differential of the actuator, allowing water to flow from
the Model DDX Deluge Valve’s pushrod chamber. As water
pressure is lost in the pushrod chamber, the supply pressure
will force the valve’s clapper open, flowing water into the re
sprinkler system piping. Water flowing into the system will flow
through the intermediate chamber of the deluge valve to a me-
chanical sprinkler alarm (if present) and will simultaneously acti-
vate the alarm pressure switch mounted in the trim. The alarm
pressure switch can electrically initiate the shut-down or start
up of equipment, such as computer, HVAC, or other secondary
alarm devices. The flow of water into the sprinkler system pip-
ing converts the dry system into a wet system. In the event that
the re subsequently produces enough heat to operate a re
sprinkler, water will flow from that sprinkler.
Listings & Approvals:
(Only when used with Reliable Trim Sets.)
1. Reliable 2” (50 mm), 2½” (65 mm), 76 mm, 3” (80 mm), 4”
(100 mm), 165 mm, 6” (150 mm) and 8” (200 mm) Electric
Actuation Single Interlock Preaction Systems, Wet Pilot Line
Single Interlock Preaction Systems and Dry Pilot Line Single
Interlock Preaction Systems are Underwriters Laboratories,
Inc. Listed and UL certied for Canada (cULus) in the Special
System Water Control Valve-Deluge Type (VLFT) category.
2. Reliable 2” (50 mm), 2½” (65 mm), 76 mm, 3” (80 mm), 4”
(100 mm), 165 mm, 6” (150 mm) and 8” (200 mm) Electric
Actuation Single Interlock Preaction Systems are certied by
Factory Mutual Approvals (FM). Factory Mutual does not ap-
prove the use of smoke detectors or cross zoned detectors in
preaction systems.
System Operation
When set correctly for service, the Model DDX Deluge Valve
is hydraulically established to separate the supply water from
the sprinkler system piping. The Reliable Model DDX Deluge
Valve is shown in both closed and open positions in Fig. 1. In the
closed position, the supply pressure acts on the underside of the
clapper and also on the pushrod through the pushrod chamber
inlet restriction. The resultant force due to the supply pressure
acting on the pushrod is multiplied by the mechanical advantage
of the lever and is more than sufcient to hold the clapper closed
against normal supply pressure surges.
To fully operate (deliver water from) a Wet Pilot Line Single In-
terlock Preaction System, two independent events must coexist
before water flow will occur. A wet pilot line sprinkler/detector
must fuse along with a re sprinkler on the system. Independent
operation of either a detector or re sprinkler will cause an alarm
to annunciate, but will not cause water discharge from the re
sprinkler system piping.
When a re is detected, the opened wet pilot line sprinkler/
detector vents the pushrod chamber to atmosphere through
the chamber outlet. Since the pressure cannot be replenished
through the inlet restriction as rapidly as it is vented, the push-
rod chamber pressure falls instantaneously. When the pushrod
chamber pressure approaches approximately one-third of the
supply pressure, the upward force of the supply pressure acting
beneath the clapper overcomes the lever-applied force thereby
opening the clapper.
To fully operate (deliver water from) an Electric Actuation Sin-
gle Interlock Preaction System, two independent events must
coexist. One electrical detector (two detectors in a cross-zoned
system) must activate and a sprinkler must open. Independent
operation of either one will cause an alarm to annunciate, but will
not cause water to discharge from the sprinkler system piping.
When a re is detected, the energized solenoid valve vents the
pushrod chamber to atmosphere through the chamber’s out-
let. Since the pressure cannot be replenished through the inlet
restriction as rapidly as it is vented, the pushrod chamber pres-
3.
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