Wet type fire sprinkler systems are the most common type of fire sprinkler installation. This system contains sprinklers heads that are connected to a water-filled piping system. The sprinklers contain either a heat reactive glass bulb or fusible component that prohibits water from discharging from the sprinkler’s orifice. The water is contained in the sprinkler piping until the time as the heat from a fire activates the fusible component, causing its release, allowing the water to discharge to the heat source. Contrary to many perceptions of automatic sprinkler systems, in this type of system, the only sprinklers that will discharge water are those sprinklers whose elements have been directly actuated by the fire. Wet systems are frequently installed in factories, warehouses, office buildings, retail stores, and residences where the potential for freezing does not exist.

A Dry type fire sprinkler system is a system that uses automatic and closed-type sprinkler heads, which are connected to a piping system containing compressed air or nitrogen, instead of water. This type of system is used where the area being protected will be unable to maintain a constant, year-round temperature of at least 40 degrees Fahrenheit.

The water supply for the system is held back by the dry-pipe valve, which will only release the water after the air pressure is evacuated from the system. The water will then flow into the piping system, and out of the sprinkler heads.

Dry Pipe Systems are frequently installed in areas subject to freezing temperatures, such as unheated storage areas, coolers and freezers, unheated parking garages, and loading docks