A Preaction System is a system that contains automatic and closed-type sprinkler heads connected to a piping system that contains air (either pressurized or non-pressurized), with an additional system of detection serving the same area as the sprinklers. These systems are typically used in applications where the accidental discharge of water would be disastrous to the usage occupancy (i.e. computer servers, telecommunications equipment, and electrical components).

Preaction Systems are similar to Dry Pipe Systems in that the water is kept from entering the piping by a valve. This valve is held closed electrically, only being released by the activation of the detection system when an electrical signal is sent to the releasing solenoid valve. The water then fills the pipe and is ready for the activation of the sprinkler heads.

A Deluge System is a system that employs open-type sprinklers that are connected to a piping system that is connected to a water supply that is kept from filling the pipe until the deluge valve is released by the additional detection system. This operates much in the same way as a preaction system. However, when the deluge valve releases the water to the system, every sprinkler in the system discharges.