A sprinkler head is a temperature-controlled valve that opens, to release a spray of water, when the heat-sensitive element reaches a specific temperature. Most sprinkler heads produced today are of the ‘glass bulb type’. The bulb is filled with a liquid and a small bubble of vapour. As heat is applied to the bulb area, the liquid expands compressing the vapour, when the vapour is fully compressed; the expanding liquid then fractures the bulb. This allows the release of the water from the supply pipework. The discharged water then strikes the deflector that controls the water distribution pattern. Sprinkler heads with an operating temperature range from 57°C to 141°C are commonly available to suit specific applications.