Wet Pipe System
Wet pipe sprinkler systems are installed more often than all other types of fire sprinkler systems. Wet pipe sprinkler sytems also are the most reliable, because they are simple, with the only operating components being the automatic sprinklers and the automatic alarm check valve They are attached to pipes containing pressurized water at all times. Individual sprinklers in the vicinity of a fire are set off by heat, allowing water to flow through them immediately.
Dry Pipe System
Dry-pipe sprinkler systems are attached to pipes that contain pressurized air. Water is not present in the piping until the system operates. When heat activates the sprinklers to open, the air pressure is reduced, allowing the dry pipe valve to open and water to flow from the sprinkler. Dry-pipe systems are usually used in spaces which the ambient temperature may be cold enough to freeze the water in a wet pipe system
Pre-Action Sprinkler System
Pre-Action Sprinkler Systems contain an additional fire-detection device that will recognize a fire before the sprinklers are activated. The sprinklers are attached to a pipe containing pressurized air. When the fire is detected by the fire alarm system, it opens the main valve, allowing water to flow through the pipes before the sprinklers are set off. When the heat activates the sprinklers, water flows through immediately, as in a wet-pipe system. Pre-action systems are usually employed in areas that are at risk for serious water damage due to damaged sprinkles. , such as in museums with rare art works, manuscripts, or books.