How do fire sprinklers work? Specifically what does the column of red liquid do?
In: Technology
It is extremely simple. There is a little glass vial holding the valve closed. When the liquid in the vial is heated, it boils to gas and expands, bursting the vial. The valve flies open, spraying water out until the main valve upstream is closed.
The thing you’re talking about has a fun name – it’s a “frangible bulb”, and it’s not always red, it can be different colors and the colors tell you what temperature the liquid in the bulb will boil, meaning they will explode because the boiling liquid turns to gas which creates pressure which means bye bye glass bulb.
Basically that bulb acts like a plug keeping the water which is pressurized in the piping from coming out, so once the bulb breaks, the plug is released, and the water sprays out.
Modern fire alarm systems will detect that water is now flowing inside the pipes and start alerts to the building and possibly the fire department that there is a fire.
That kind of sprinkler, or “fire protection” system is always charged with pressurized water. Since the water is stagnant in the pipes it is black and smelly and nasty which action movies definitely underplay. I work in office space construction and my clients are always, oh, just drain down the sprinklers during the day we don’t want to pay overtime… and then we do and they’re, like, oh… oh god… please stop.
This is also why it’s important that they are installed within ceilings, by the way. Because they need the hot gas and smoke from fires to build up to boil the liquid. If placed the head in the ceiling but then removed the “ACT” (the removable ceiling tiles most offices have) the heat would up above the head and not trigger it until enough smoke built up that it went down the head’s level, which in a modern office building could be several feet meaning the fire has gotten much worse. So a lot of NFPA codes are being enforced now regarding how you can work within “open” ceilings and the height of the sprinkler heads.
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