Technical data

17.
1.3.4 Model H Type D
The Reliable Model H 1-1/2” (40mm) Double Interlock Preaction System Type D is an electrically actu-
ated system that utilizes a normally closed, quick-opening hydraulically-operated diaphragm actuated
solenoid as the main system control valve. In the normal condition (de-energized), water pressure is
held at the solenoid valve inlet. When the programming logic of the release panel has been satisfied,
the panel opens (energizes) the solenoid valve allowing water flow into the protected area. The Type D
system is described as an electric/electric double interlock preaction system. Two independent con-
ditions must coexist to satisfy the double interlock programming in the release panel. For the Type D
system, these two conditions are (a) activation of the detection system and (b) signal of low pneumatic
pressure in the system piping. Detection systems are more sensitive than the sprinklers on the system,
and will activate prior to the sprinklers opening. The time period between fire detection/alarm and
opening of the sprinklers allows the building owner a chance to respond and possibly avoid unneces-
sary discharge of water into the water sensitive environment. In the event the alarm is not attended to,
the fire will continue to grow eventually fusing one or more sprinklers and relieving pneumatic pressure
in the system. Loss of pneumatic pressure results in a signal from the pressure switch. When this sec-
ond condition (low pressure signal) coexists with the first condition (detection), the release panel en-
ergizes (opens) the solenoid valve flowing water into the protected area. Alarm devices are activated
upon the flow of water into the sprinkler system piping. Pneumatic pressure can be provided from a
tank-mounted compressor, plant air system, or nitrogen cylinders, and must be maintained by a Reli-
able Model A-2 listed pressure maintenance device*. Pneumatic pressure is monitored by a pressure
switch* that will notify the owner in the event of falling pressure due to sprinkler damage, pipe dam-
age, or failure of the compressed gas system. A low pressure condition in the absence of a detection
signal or a detection signal in the absence of a low pressure condition will NOT result in activation of
the solenoid and main system control valve. The singular condition can be corrected and the system
returned to normal service.
*Note: For Type D systems, the Reliable Model A-2 Pressure Maintenance Device and the System Sen-
sor Model EPS10-2 Pressure Switch are provided with the trim.
Approvals and technical data for the Model H Double Interlock Preaction System Type D can be found
on Reliable Automatic Sprinkler Company Bulletin 720.
Figure 15