be plated for appearance or they maybe coated for
protection from an adverse environment. For example,
sprinklers that will be used in corrosive atmospheres
are either lead- or wax-coated. Finally, automatic
sprinklers are normally held closed by heat-sensitive
elements that press down on a cap over the sprinkler
orifice and are anchored by the frame of the sprinkler.
The heat-sensitive elements melt and release at
different temperatures depending on application.
Sprinklers are color coded to identify the temperature
range rating of the fusible element (table 8-1). Color
coding is not required for plated sprinklers, ceiling
sprinklers, or similar decorative types.
There are basically four types of release
mechanisms for automatic sprinklers. They are the
fusible link, frangible bulb, frangible pellet, and
Figure 8-14.Fusible link automatic sprinkler.
The fusible link sprinkler (fig. 8-14) is kept closed
by a two-piece link held together by a solder with a
predetermined melting point. When the solder melts,
the levers pull the two-piece link apart and fly away
from the sprinkler. Pressure in the piping network
pushes the cap from the orifice of the sprinkler to
The frangible bulb sprinkler (fig. 8-15) has a
small bulb made of glass between the orifice cap and
the sprinkler frame. The bulb is partially filled with a
liquid. Air fills the remaining space. Heat from a fire
will cause the liquid to expand against the air causing
the glass bulb to shatter and opening the sprinkler for
Figure 8-15.Frangible bulb automatic sprinkler.
Table 8-1.Sprinkler Temperature Ratings