A dry pendent sprinkler (fig. 8-18) is used when
pendent sprinklers must be placed on dry pipe
systems or in wet pipe systems when the area to be
protected is subject to freezing (such as a walk-in
reefer or outside shop area) and the piping network
is installed in a heated area. This sprinkler is fitted
with a tube within an attached pipe. The tube holds
the water sealing elements in place against a
watertight seal at the top of the pipe. When the
sprinkler is actuated, the tube drops down and
releases the elements through the tube and out the
open sprinkler with the water discharge.
Open sprinklers consist only of a sprinkler
frame and deflector. They are used on special
sprinkler systems such as deluge or rapid reaction
systems (fig. 8-19).
Water spray nozzles (fig. 8-20) are used for
special application of water in various patterns (for
example, wide or narrow angle, long throw or flat
patterns). The different patterns may be achieved by
either internal or external deflection of the water
stream depending on the type of nozzle.
Figure 8-18.Dry pendent automatic sprinkler.
SPRINKLER SYSTEM DETECTION
AND INDICATING DEVICES
Sprinkler systems have many different con-
trolling devices and fittings. These can be classified
as detecting or initiating devices or fittings. Their
function is to detect system operation and to initiate
system operation or alarm systems connected to the
sprinkler system. This section discusses these
devices and fittings to aid you in installing and
understanding the interface between the mechanical
and electrical functions of these devices.
Water-Flow Actuated Detectors
Sprinkler water-flow detectors are generally
switches are used on both wet and dry pipe systems.
Vane switches are widely used on wet pipe sprinkler
systems. They cannot be used on dry pipe systems
because the initial rush of water into the pipe could
damage the vane and mechanism.
Dry pipe system alarms tend to be slow-acting
because it takes time to lose sufficient air through a
fused sprinkler to trip the system. Various methods
are used to speed up dry pipe systems as discussed
Wet pipe system alarms have a different
problem. Fluctuating water pressure frequently
causes flow into a sprinkler system, equalizing the
sprinkler system pressure with the supply pressure.
Such surges of water or of pressure cause false
water-flow alarms if some method of slowing
Figure 8-19.Open sprinklers.