Wet pipe systems are the most common fire sprinkler system. A wet pipe system is one in which water is constantly maintained within the sprinkler piping. When a sprinkler activates this water is immediately discharged onto the fire.
NFPA 13 states that a wet pipe sprinkler system employs “automatic sprinklers attached to a piping system containing water and connected to a water supply so that water discharges immediately from sprinklers opened by heat from a fire.”
A dry pipe sprinkler system is…well…dry. There is no water in it, that is, at least until there is a fire. In the event of a fire, water is released by a valve to fight the fire. Dry systems are essential for areas exposed to freezing conditions, such as outdoor storage areas, canopies, parking garages and unconditioned attics.
NFPA 13 states that a dry pipe sprinkler system employs “automatic sprinklers that are attached to a piping system containing air or nitrogen under pressure, the release of which (as from the opening of a sprinkler) permits the water pressure to open a valve known as a dry pipe valve, and the water then flows into the piping system and out the opened sprinklers.”
A preaction system is like a dry system, in that there is no water in the pipes until a fire. However, in a preaction system there is added protection against an accidental system trip. Basically, preaction systems are great for museums, data centers or anywhere else where giving something an accidental shower could cost big bucks.
NFPA 13 states that a preaction sprinkler system employs “automatic sprinklers that are attached to a piping system that contains air that might or might not be under pressure, with a supplemental detection system installed in the same areas as the sprinklers.”
The purpose of a deluge system is simple: Get a lot of things wet—fast! On a deluge system all of the sprinkler heads are “open”, which means if the system trips every sprinkler head will be flowing water. This type of system has erroneously stared in more Hollywood movies than Tom Cruise.
NFPA 13 states that a deluge sprinkler system employs “open sprinklers that are attached to a piping system that is connected to a water supply through a valve that is opened by the operation of a detection system installed in the same areas as the sprinklers. When this valve opens, water flows into the piping system and discharges from all sprinklers attached thereto.”