What does a frangible bulb do in a sprinkler head?

A frangible bulb in a sprinkler head is a key component designed to activate the sprinkler system when a certain temperature threshold is reached. This bulb contains a liquid that expands as it heats up. When the temperature exceeds the specified limit, the liquid expands to a point where it causes the bulb to break. This breaking action is crucial because it allows water to flow from the sprinkler head to extinguish the fire.

The function of the frangible bulb is specifically focused on heat response rather than pressure or the regulation of water flow. It does not close the water supply, activate an alarm system, or regulate water flow itself. Instead, its primary role is to act as a trigger for the sprinkler to engage and release the water necessary for firefighting efforts.