In a preaction system, all sprinklers are closed and normally there is no water in the piping. A preaction system is used when faster response is desired (versus a dry pipe system). When fire occurs, a supplementary detection system (more sensitive than the sprinkler elements) senses the fire and automatically opens a water control valve which
allows water to flow into the piping system. Subsequent water discharge occurs from individual sprinklers as they respond to the heat of the fire. The system shown below uses HAD’s (Heat Actuated Detectors) and a dropweight release to open the preaction valve. Alternate detection systems can also be used. Pre-priming foam solution is not needed as foam will be proportioned into the piping during operation.
