The Difference Between a Glass Bulb and Fusible Link Fire Sprinkler

Fire sprinkler heads have different heat-sensitive elements that allow the water to flow out of the head and suppress a fire. The two main options are a glass bulb and a fusible link fire sprinkler. They both serve the same essential function; to react after a specific temperature range is reached and release water. That way, only sprinkler heads nearest the fire activate, and there is no movie-style torrent of water from ALL sprinklers. So what is the difference between a glass bulb and a fusible link fire sprinkler head?

Fusible Link Fire Sprinkler

A fusible link fire sprinkler head has two metal plates bonded by a fusible metal alloy or solder that hold the pip cap, or plug, in place. This alloy is the heat-sensitive element that reacts when the temperature around it reaches a point where the temperature rating allows it to react. The solder will melt, and the metal plates detach. The water can flow when the pip cap releases after the plates detach.

fusible link fire sprinkler

Glass Bulb Fire Sprinkler

Instead of metal plates and solders like those in a fusible link fire sprinkler, some sprinkler heads have a glass bulb with colored fluid inside. In this case, it is the liquid that is heat sensitive. It reacts to heat by expanding when a specific temperature range is reached and breaks the glass bulb. The pip cap then releases allowing water to flow from the system. Glass bulb sprinkler heads are often given more popularity simply for aesthetic reasons.

glass bulb fire sprinkler


While these two differ in reactions, there are a few notable similarities. They each have different temperature rating options, with 135 degrees Fahrenheit being the lowest and 650 degrees Fahrenheit the highest. The temperature rating is the temperature zone in which the glass bulb will burst, or the fusible link will melt, setting off the sprinkler. These temperature ratings are often given color indications, which is more the case with glass bulbs than fusible link fire sprinklers.

We work with both glass bulb and fusible link fire sprinkler heads! Do you need service on your fire sprinklers or need fire sprinklers installed at your property? Call Valley Fire Protection & Plumbing to set up a service call or start a quote today.

Related Topics: Fire Protection // Fire Sprinkler
By: Matt Clegg
As an executive at Valley Fire Protection, Matt’s desire is to provide the best fire protection and engineering experience for Valley Fire customers. By thinking outside the box, and by educating and equipping clients with the information they need to help them properly protect their buildings, Matt and his team have contributed to a long list of successful projects.


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    It really interests me to read such articles, thanks for sharing. Blogs like yours really helps me learn more day by day.

    • Matt Clegg

      Thank you Alice for your kind words. At Valley Fire we really like to provide useful information for our visitors.


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