Grades 3–5 · Systems
Why doesn’t every fire sprinkler spray at once?
In many buildings, water waits inside pipes above the rooms. Each sprinkler head holds back that water with a seal. A small heat-sensitive part keeps the seal in place, so ordinary pipe pressure does not make every head spray.
In the diagramLocal heat releases an individual sprinkler headA glass-bulb, water-filled-pipe exampleReleased: water spraysOther head: still sealedBulb goneDeflectorSmoke alone does not release these sprinkler heads.
One common design uses a glass bulb containing liquid. Heating makes the liquid expand. When the bulb reaches its designed operating condition, it breaks and the sealing parts release. Water can then pass through that opening. It strikes a shaped metal deflector that spreads the flow into a spray.
Each head has its own release element. A nearby head can open while another stays closed because its element has not become hot enough. More heads can open if heat reaches them. Smoke alone does not release the glass bulbs, and a sounding smoke alarm does not automatically open them. Some sprinkler systems use different designs; the drawing explains this common water-filled-pipe example.
About this explanation
Starting knowledge: Understand that heating can expand a liquid and that a seal can hold water back.
Sources
- US Fire Administration — Home Fire Sprinklers
- Viking Group — Sprinkler 70h: Operation