There are a number of different types of sprinkler heads that meet different needs. This article covers the operation types (fusible link vs. bulb), the distribution types (pendant, upright, sidewall), and response temperatures.
Fusible Link Sprinklers vs. Glass Bulb Sprinklers
All wet-pipe sprinklers are held closed by either a fusible link or a glass bulb that contains a heat-sensitive liquid.
A fusible link sprinkler head has a two-part metal element that is fused by a heat-sensitive alloy. The link holds the pip cap, or plug, in place. Once the ambient temperature around the sprinkler head reaches a specified temperature, the alloy releases and the metal elements separate, which causes the pip cap to fall away. Water is then released. Note that water is only released by sprinkler heads where the ambient temperature reaches a specified level - therefore, water is only released in the area of a fire, which helps limit water damage.
Glass bulb sprinkler heads have a small glass reservoir that holds a heat-sensitive liquid. This glass bulb holds the pip cap in place. When the ambient temperature of the liquid reaches a certain level, the liquid expands causing the glass bulb to break, which allows the pip cap to fall away releasing water. As with the fusible link heads, water is only released where the ambient temperature reaches a certain level, which helps limit water damage.
Sprinkler Response Temperatures
Since ambient air temperatures can vary widely depending on the use of a space or surrounding environment, sprinklers come rated for different activation temperatures. The table below is based on NFPA 13 table 3-2.5.1 (US National Fire Code); however, manufacturers may have sprinklers with different temperature ratings.
|Classification||Maximum Ceiling Temperature||Sprinkler Activation Temperature||Glass Bulb Color||Fusible Link Color|
|Ordinary||100°F||135°F - 170°F||Orange (135°F)
|black; no color|
|Intermediate||150°F||175°F - 225°F||Yellow (175°F)
|Extra High||300°F||325°F - 375°F||Purple||Red|
|Very Extra High||375°F||400°F - 475°F||Black||Green|
|Ultra High||475°F||500°F - 575°F||Black||Orange|
Sprinkler Head Distribution Types
The following diagrams show the different types of sprinkler heads and their distribution patterns. Refer to manufacturer information for coverage radii.
Pendant Sprinkler Head
Pendant sprinkler heads hang down from the ceiling and spray water in a circle pattern.
Concealed Pendant Sprinkler Head
Concealed pendant sprinkler heads are recessed in a ceiling and are covered with a decorative cap. The cap will fall away about 20°F prior to activation of the sprinkler. Once the sprinkler reaches its rated activation temperature, the head will drop below the ceiling. The water pattern of concealed sprinkler heads is a circle.
Upright Sprinkler Head
Upright sprinkler heads project up into a space and have deflectors that spray the water downward. They are generally used in mechanical rooms or other inaccessible areas to provide better coverage between obstructions like beams or ducts. They also provide a circle spray pattern.
NFPA 13 dictates that the frame arms of the sprinkler head should be parallel to the branch line. This helps limit the amount of shadowing (areas that don't receive a spray of water since they are blocked by the frame or branch pipe.) The diagram below show this orientation.
Side Wall Sprinkler Head
Side wall sprinkler heads stand out from a wall and have a deflector that sprays water away from the wall in a half-circle spray pattern. A second deflector also sprays water back toward the wall so that the wall is protected. These are used when sprinklers cannot be located in the ceiling.