An Overview Of Glass Bulb And Fusible Alloy Fire Sprinklers

Aug 5, 2023 | Company News, News

Fire sprinklers are a critical component of automatic suppression systems that detect and extinguish building fires. The sprinkler head contains a thermally-activated element that melts or shatters to open the water valve and spray when exposed to heat from a fire. Glass bulb and fusible alloy sprinklers provide reliable activation through different triggering mechanisms. Understanding how they work and key design differences helps ensure optimal fire protection.

Fire Sprinklers

What Are Fire Sprinkler Heads?

Fire sprinklers are heat activated ceiling or wall-mounted devices connected to a network of water-filled pipes. Key components include:

  • Fusible element – glass bulb or alloy link that fails when heated to a specific temperature.
  • Deflector – spray plate that distributes water droplets over the coverage area.
  • Valve assembly – compressed seal and orifice kept closed by the fusible element.
  • Frame arm – supports the deflector and valve components.
  • Inlet connection – threaded or grooved end to connect the sprinkler to piping.

When heat from a fire raises the temperature at the sprinkler head, the fusible element breaks apart. This releases the valve seal, opening the orifice and allowing water to spray out the deflector over the fire source. Quick suppression minimizes damage and prevents flashover.

Key Benefits of Fire Sprinklers:

  • Detect fires automatically without need for manual activation.
  • Effective suppression from above using targeted water spray.
  • Prevent flashover and reduce toxic smoke hazards.
  • Control and often extinguish fires prior to firefighter arrival.
  • Enable safe building evacuation during a fire event.
  • Integrate with alarm systems to notify building occupants and authorities.
  • Require far less water than exterior fire hoses to suppress a fire.
  • Help meet building fire safety regulations and insurance requirements.

Glass Bulb Fire Sprinkler Operation

The most common design is the glass bulb sprinkler. A small glass vial filled with temperature sensitive fluid is attached to the valve assembly. When heated, the fluid expands which shatters the glass and releases the valve seal.

Glass bulb sprinklers offer these benefits:

  • Color coded bulbs for specific activation temperatures from 155°F to 360°F.
  • Tempered Pyrex or borosilicate glass for reliable shattering.
  • Fluid doesn’t evaporate over time leading to false activation.
  • Thin bulb wall provides fast thermal response.
  • Audible popping reports activation and allows testing.
  • Inexpensive components make glass bulbs most cost effective option.

Fusible Alloy Link Sprinklers

Fusible Alloy Fire Sprinkler use a metallic link rather than glass bulb to secure the valve. Common alloys are eutectic solder mixes like bismuth, lead, tin that melt at a fixed temperature.

Advantages of fusible alloy sprinklers:

  • Alloys available for exact melting points from 165°F up to 400°F.
  • Mix multiple alloys to get specific activation temperature.
  • Metallic link resists accidental breakage during handling.
  • Does not require perfectly axial forces for consistent release.
  • Suitable for harsh environments with shaking, pressure fluctuations.
  • Lasts longer than glass without deterioration.

While glass works well for most applications, fusible alloy links provide very precise and reliable activation for specialty high temperature sprinklers.

Key Sprinkler Design Considerations

  • Coverage area and spray pattern density to sufficiently wet surfaces.
  • Placement and obstruction avoidance to spray water directly on potential fire sources.
  • Activation temperature that matches potential heat exposure risks.
  • Response Rating index including RTI, C-factor for sensitivity.
  • End connection size, thread type, and pipe orientation.
  • UL listing and approval from FM Global or LPCB for the hazard occupancy type.
  • Color coding to identify temperature rating and type.
  • Local sprinkler installation guidelines and codes.

With their fast automatic operation and lifesaving fire suppression capabilities, fire sprinkler systems provide an invaluable level of protection. Selecting the optimal sprinkler technology and design ensures building occupants, assets, and operations remain safe from fire.