Wet Pipe Sprinklers
Wet Pipe sprinklers are the most common type of fire sprinkler systems and the most reliable, with the only operating components being the automatic sprinklers and, in some instances, the automatic alarm check valve. An automatic water supply provides water under pressure to the system piping and all the piping is filled with water. When an automatic sprinkler is exposed to sufficient heat, the heat-sensitive element (glass bulb or fusible link) releases water from that sprinkler. Wet pipe sprinklers react to a specific range of temperatures.
Dry Pipe Systems
Dry Pipe systems are used only in spaces in which the ambient temperature may be cold enough to freeze the water in a wet pipe system, such as unheated buildings, parking garages, outside canopies attached to heated buildings and refrigerated coolers. Dry pipe systems are the second most common fire sprinkler. Disadvantages include increased complexity, higher installation and maintenance costs, increased fire response time and increased corrosion.
Deluge systems are systems that have open sprinklers – the heat-sensing operating element is removed or specifically designed to be open so that all sprinklers connected to the water piping system are open. Deluge systems are used for special hazards where rapid fire spread is a concern, as they provide a simultaneous application of water over the entire hazard, and are commonly seen as preventive measures to prevent egress of fire from an external source, such as high-rise windows, warehouse bay entries and openings in a fire-rated wall. Water is not present in the piping until the system operates.
Pre-Action systems are hybrids of wet, dry and deluge systems, depending on requirements. There are two main sub-types of pre-action systems: single interlock and double interlock. Single interlock systems are similar to dry systems except that they require a preceding fire detection event, typically the activation of a heat or smoke detector. Double interlock systems are similar to deluge systems except that automatic sprinklers are used. Pre-action sprinkler systems are commonly used in museums with rare works or art, manuscripts or books, and data centers.