Today we're diving into the basic components of a fire sprinkler:
The orifice varies in size, but has a major impact on the sprinkler's k-factor which ultimately governs the sprinkler's relationship between flow and pressure. Opening sizes vary fairly dramatically but in general are not a major driver for sprinkler selection.
The nominal threading sizes range in quarter-inch increments from 1/2-inch to 1-1/4-inch (although some dry pendent shafts do have 1-1/2-inch threads). Thread size of sprinklers can be gathered in the field simply by measuring the diameter of the thread shaft. Sprinklers with a k-factor greater than 5.6 are no longer allowed to have thread sizes of 1/2-inch (NFPA 13 2002-2016 Section 8.3.5).
The plug retains the water (and pressure) within the sprinkler and pipe network. Breakage of the liquid-filled glass bulb results in the release of the plug, and thereafter the water.
Sealed Liquid-Filled Glass Bulb
Modern commercial sprinklers mostly rely on the colored glass bulb as the thermal sensor in the fire sprinkler, but other types are still frequent as well. Color of the liquid within the bulb indicate the listed activation temperature of the sprinkler (and can be found in NFPA 13 2002-2016 Table 220.127.116.11).
Frame & Deflector
The frame can have many finishes, of which some of the more common are listed above. The deflector offers the basic premise of the fire sprinkler - which is to distribute water in a specific pattern to best combat a fire hazard within an enclosure. Deflectors vary depending upon the style of the sprinkler and work to achieve different objectives. A residential pendent, for example, throws water with greater emphasis to the walls and ceiling where hazards are more commonly present in residential occupancies.
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Joe Meyer, PE, is a Fire Protection Engineer out of St. Louis, Missouri who writes & develops resources for Fire Protection Professionals. See bio here: About