How does a automatic fire sprinkler head work?

An automatic fire sprinkler system head is a valve, that when the temperature sensitive bulb reaches its predetermined fixed temperature, expands, breaks and then allows the free flow flow of water.

Russ Porteous
CEO, Firewize
26 Jul, 2019

An automatic fire sprinkler system head is a valve, that when the temperature sensitive bulb reaches its predetermined fixed temperature, expands, breaks and then allows the free flow flow of water.

Sprinkler Head Operation

Fire Sprinkler Head Components

The glass bulb for an automatic fire sprinkler head is the active component that breaks when it reaches its nominal operating temperature.  There are generally two sizes of the glass bulb;

  • 3mm - Quick Response
  • 5mm - Standard Response

Due to thermal conductivity, the thinner (3mm) quick response will respond more quickly to a rise in temperature and operate more quickly than the 5mm standard response.

Fire Sprinkler Head Components

 

Sprinkler Head Operating Temperatures

The glass bulb or fusible link in an automatic fire sprinkler system is calibrated to operate at a designated temperature. Sprinkler heads are selected and installed taking into consideration the use, location and typical ambient operating temperatures.

The Standard AS 2118.1 states that the temperature rating chosen shall be not less than 30ºC above the highest anticipated temperature conditions except under specific conditions;

  1. Under glazing, translucent plastics and uninsulated metal roofs, in unventilated concealed spaces and show windows on external walls, and in other locations that are directly exposed to the sun, it may be necessary to install sprinklers with a temperature rating between 79°C and 100°C.
  2. n High Hazard systems protecting high piled storage, sprinklers having a nominal temperature rating of 141°C shall be used at the roof or ceiling roof or ceiling, except where in the case of special sprinklers, the listing, manufacturers published data sheets and codes and standards referenced herein, recommend an alternative temperature rating.
  3. Where high temperature sprinklers are installed within drying ovens or hoods over papermaking machines and the like (see Clauses 5.6.14 and 5.7.6), sprinklers at the ceiling or roof immediately over and to a distance of 3 m beyond the boundary of such structures shall be of the same temperature rating, subject to a maximum of 141°C.
Sprinkler Head Operating Temperatures
ºC ºF Colour
Automatic Fire Sprinkler Bulb Operating Temperatures
57ºC 135ºF Orange
68ºC 155ºF Yellow
93ºC 200ºF Green
141ºC 286ºF Blue
182ºC 360ºF Purple