the supervised system should record in inches of
water rather than pounds per square inch. The second
system is the unsupervised pre-action system. It has
no means of continuous monitoring.
A combined system (fig. 8-12) is a special purpose
arrangement using two modified dry pipe valves
connected to tripping devices and piped in parallel to
supply water to the same sprinkler system. The piping
net work is filled with air under pressure. When a fire
is detected, an exhauster at the end of the system
opens and releases the air within the system. The
system then operates the same as a pre-action system.
However, if the detection system fails, the combined
system acts the same as a dry pipe system and allows
water to be admitted to the system when the
sprinklers open, discharging the air from the piping
TUBING OR WIRING TO FIRE DETECTION SYSTEM
Figure 8-12.Combined system header arrangement.
TYPES OF SPRINKLERS
Sprinklers are nozzles placed at intervals along
the piping network to distribute a uniform pattern of
water on the area being protected. To attain
maximum efficiency, the stream of water must be
broken into droplets. A deflector (part of the frame of
the sprinkler) breaks up the water.
You, as a UT, will generally install sprinklers to
meet the specifications and plans of a project. When
you require more information on proper locating of
sprinklers, refer to the National Fire Protection
Association Code Book Number 13 (NPFA #13),
entitled Installation of Sprinkler Systems.
Automatic sprinklers are designed for specific
applications based on orifice size, deflector design,
frame finish, and temperature rating. Sprinklers have
orifices ranging in size from 1/4-inch to 1/2-inch
diameter graduated by 1/16-inch increments. There is
also one 17/32-inch size orifice. Deflectors give
different patterns of water distribution and allow the
sprinkler to be placed in various locations such as
upright, pendent, or sidewall (fig. 8-13). Next,
sprinkler frames may
Figure 8-13.Sprinkler deflector styles.