+44 (0) 1787 223232 [email protected]



A glass sprinkler bulb is the most reliable and economic device used to actuate a fire sprinkler head. The frangible bulb is simple to use, comprising a small thermo bulb made of glass containing a chemical liquid that will expand rapidly when exposed to rising temperatures, bursting the glass sprinkler bulb at an accurately pre-determined temperature, thereby activating the sprinkler.

Drawing on more than 50 years’ experience in glass bulb technology, Day-Impex offer a bulb for every design of head, and for every fire risk application.

A range of sizes, with diameters from 12mm down to 2.5mm, is available in lengths to suit all sprinkler frame designs, with aesthetically pleasing results.

Extensive research into formulating chemical liquids with known, precise expansion rates, ensures that all bulbs meet specific performance standards required by approval authorities throughout the world.

Precision engineering and exhaustive quality control in every stage of production ensure that the four most critical bulb characteristics are achieved.

  • Uniform and consistent size
  • High mechanical strength
  • Highly accurate operation temperature within
    tight tolerances
  • Consistent RTI values

The entire manufacturing process carries certification to the Quality Standard ISO9001:2015, and most bulbs meet the new European Standard, EN12259. Day-Impex Glass Bulb Type 937 carries LPCB Product Approval in various rated temperatures.

Day-Impex Glass Bulbs Types 937 and 941 carry UL Component Recognition in various rated temperatures.



These products are also referred to as Frangible Bulbs, Glass Sprinkler Bulbs and Thermo Bulbs.

CALL DAY-IMPEX ON 01787 223232 

The trend to make sprinklers operate faster to suppress fire and restrict spread has seen Day-Impex develop a progression of new glass bulb designs.

Reducing the bulb diameter, but maintaining strength, researching and selecting faster-expanding liquids, has resulted in new bulbs to meet every challenge, including the residential and ESFR standards of UL, FM, EUROPE and KOFEIS in Korea.



MON - THURS | 9:00 AM - 5:00 PM

FRI | 9:00 AM - 4:00 PM



Company Number: 415552


+44 (0)1787 223232


Day-Impex Limited
Station Works
Earls Colne, Colchester
Essex CO6 2ER
United Kingdom