Technical data

9.
1.2.1 Model DDX Wet Pilot Line Single Interlock
A wet pilot line is a non-electrical type of detection/release system that can be used in conditioned (i.e.
freeze protected) areas. Closed sprinklers or fixed-temperature-release pilot line detectors are installed
throughout the protected area on small diameter piping that contains water under pressure. The wet
pilot line is an extension of the Model DDX Deluge Valve push-rod chamber. Upon activation of a pilot
line sprinkler or pilot line detector, pressure is released from the pilot line and push-rod chamber allow-
ing the Model DDX Deluge Valve to open and fill the system piping in the protected area. Please note
that water will discharge from the pilot line sprinkler or detector(s) upon activation. Alarm devices are
activated upon the flow of water into the sprinkler system piping. In the event the fire continues to grow,
individual fire sprinklers in the protected area will be activated similar to a wet pipe system. Wet pilot
trim is the basis on which dry pilot line and electrical actuation systems are built; additional compo-
nents are added to the wet pilot trim for each of these systems. It is important to note that the length and
height of wet pilot lines may be limited by the available system water pressure (see bulletins referenced
below). For supervised systems (required when there are more than 20 sprinklers), pneumatic pressure
can be provided from a tank mounted compressor, plant air system, or nitrogen cylinders, and must
be maintained by a listed pressure maintenance device such as the Reliable Model A-2. Pneumatic
pressure is monitored by a pressure switch that will initiate a signal in the event of falling pressure due
to sprinkler damage, pipe damage, or failure of the compressed gas system. The Reliable Model B-SI
and Model C-SI Air Compressor Panels are specifically designed for single interlock preaction systems
up to 200 gallon capacity and incorporate an air compressor, regulator, pressure switch, and output
relays in a convenient wall mount cabinet (see section 2.3.1).
Approvals and technical data for Model DDX wet pilot line single interlock preaction systems can be
found on Reliable Automatic Sprinkler Company Bulletin 749.
Figure 7