Viking designs use belleville spring seals to close the waterway of its sprinklers. With Viking sprinklers, force is transmitted from a set-screw through a fusible element or glass bulb to a belleville spring seal to close the waterway. When the sprinkler is heated to its operating temperature, and the fusible element or glass bulb activates, the tension on the spring is released causing the belleville spring seal to open the waterway even if there is no water pressure in the sprinkler.

Why is it important that Viking NEVER used O-rings to seal the waterway of their sprinklers?

To read about
UL Investigates Sprinklers with O-rings
http://www.ul.com/about/newsrel/gbsprnklr.html

To read about
UL Urges Testing of Dry Sprinklers
http://www.ul.com/about/newsrel/nr030300.html

To read about
CPSC recall of Dry Sprinklers
http://www.cpsc.gov/cpscpub/prerel/prhtml99/99152.html

To read about
Mealane Cprporation recall of "Star" Dry Sprinklers
http://www.star-recall.com
(From home page, be sure to click on NEXT PAGE)

To read about
FM Global Alert*.
http://www.fmglobal.com/whats_new/press_center/releases/20000208.html

Omega Recall
http://www.cpsc.gov/cpscpub/prerel/prhtml99/99008.html