Operation
Each closed-head sprinkler is held closed by either a heat-sensitive glass bulb (see below) or a two-part metal link held together with fusible alloy such as Wood's metal and other alloys with similar compositions. The glass bulb or link applies pressure to a pip cap which acts as a plug which prevents water from flowing until the ambient temperature around the sprinkler reaches the design activation temperature of the individual sprinkler. Because each sprinkler activates independently when the predetermined heat level is reached, the number of sprinklers that operate is limited to only those near the fire, thereby maximizing the available water pressure over the point of fire origin.
The bulb breaks as a result of the thermal expansion of the liquid inside the bulb. The time it takes before a bulb breaks is dependent on the temperature. Below the design temperature, it does not break, and above the design temperature, it takes less time for higher temperatures. The response time is expressed as a response time index (RTI), which typically has values between 35 and 250 m½s½, where a low value indicates a fast response. Under standard testing procedures (135 °C air at a velocity of 2.5 m/s), a 68 °C sprinkler bulb will break within 7 to 33 seconds, depending on the RTI. The RTI can also be specified in imperial units, where 1 ft½s½ is equivalent to 0.55 m½s½. The sensitivity of a sprinkler can be negatively affected if the thermal element has been painted.
| Maximum Ceiling Temperature | Temperature Rating | Temperature Classification | Color Code (with Fusible Link) | Glass Bulb Color |
|---|---|---|---|---|
| 100°F / 38°C | 135-170°F / 57-77°C | Ordinary | Uncolored or Black | Orange (135°F) or Red (155°F) |
| 150°F / 66°C | 175-225°F / 79-107°C | Intermediate | White | Yellow (175°F) or Green (200°F) |
| 225°F / 107°C | 250-300°F / 121-149°C | High | Blue | Blue |
| 300°F / 149°C | 325-375°F / 163-191°C | Extra High | Red | Purple |
| 375°F / 191°C | 400-475°F / 204-246°C | Very Extra High | Green | Black |
| 475°F / 246°C | 500-575°F / 260-302°C | Ultra High | Orange | Black |
| 625°F / 329°C | 650°F / 343°C | Ultra High | Orange | Black |
From Table 6.2.5.1 NFPA13 2007 Edition indicates the maximum ceiling temperature, nominal operating temperature of the sprinkler, color of the bulb or link and the temperature classification.
Read more about this topic: Fire Sprinkler
Famous quotes containing the word operation:
“An absolute can only be given in an intuition, while all the rest has to do with analysis. We call intuition here the sympathy by which one is transported into the interior of an object in order to coincide with what there is unique and consequently inexpressible in it. Analysis, on the contrary, is the operation which reduces the object to elements already known.”
—Henri Bergson (1859–1941)
“Human knowledge and human power meet in one; for where the cause is not known the effect cannot be produced. Nature to be commanded must be obeyed; and that which in contemplation is as the cause is in operation as the rule.”
—Francis Bacon (1560–1626)
“It requires a surgical operation to get a joke well into a Scotch understanding. The only idea of wit, or rather that inferior variety of the electric talent which prevails occasionally in the North, and which, under the name of “Wut,” is so infinitely distressing to people of good taste, is laughing immoderately at stated intervals.”
—Sydney Smith (1771–1845)