Technical data

19.
1.5 Low Pressure Dry System
Low pressure dry pipe systems offer numerous advantages over conventional systems. Conventional dif-
ferential dry pipe systems rely on pneumatic pressure above a pool of priming water to hold a check valve
clapper closed and prevent supply water from flowing into the system. When pneumatic pressure is lost, the
clapper opens, and the incoming water works against the pressurized gas as it makes its way through the
system piping. By lowering the pneumatic pressure in the system, water can move faster through the piping
since there is less pneumatic pressure working against it. Faster water movement from the valve to the end
of the system improves water delivery time, permits the installation of larger and possibly fewer dry systems,
and often results in the elimination of accelerators. Lower pressures require smaller air compressors, nitro-
gen generators, and/or nitrogen tanks, and the DDX technology eliminates the need for priming water that
evaporates over time resulting in excessive corrosion in the piping. Because conventional valves operate on
a surface area differential principle and are non-latching, they can be subject to false activation in the event
of pressure surges in the water supply. Reliable Model EX and DDX-LP dry systems incorporate a latching
type clapper that is held closed by the incoming water supply. Any increase in water pressure attempting
to force the clapper open is offset with equal pressure in the latching mechanism supply line. The Reliable
Automatic Sprinkler Company offers two low pressure dry systems—the Model EX for domestic use, and the
Model DDX-LP for domestic or international use.
Figure 18
Figure 17