A Pre-Action Sprinkler System is a system which employs automatic and closed-type sprinkler heads connected to a piping system that contains air (either pressurized or non-pressurized), with a supplemental system of detection serving the same area of protection. These systems are typically used in applications where an accidental discharge of water would be catastrophic, such as computer servers, telecommunications equipment, and high voltage electrical components.
Pre-Action Systems are similar to Dry Pipe Systems in that the water is prevented from entering the piping by a valve, in this case a pre-action valve. When the detection system is activated by the heat or smoke detectors, an electric signal sent to the releasing solenoid and the valve opens. The water then fills the pipe and is ready to flow through the sprinkler heads that are activated. Pre-Action Systems can be designed to be activated by only one detection device type or many.
A Pre-Action System can also be combined with a Dry Pipe System, for use in areas that are unheated, or in areas where the occupant does not want in the piping system prior to the activation of a sprinkler head. This is called a Double-Interlocked Pre-Action System.
Common installations include computer rooms, process control rooms, data storage, and telecommunications rooms.