A pre-action system is a type of fire protection system that combines elements of both dry and wet pipe sprinkler systems. It’s typically used in areas where water damage from accidental sprinkler activation needs to be minimized, such as data centers, museums, libraries, and other facilities with sensitive equipment or valuable assets.

Here’s how a pre-action system generally works:

1. Pipe Network: Like a wet system, a pre-action system consists of a network of pipes throughout the protected area. However, these pipes are typically dry, meaning they’re not filled with water until the system is activated.
2. Water Supply: The system is connected to a water supply, similar to wet systems, but the water is held back from entering the pipes by an electrically operated valve known as a pre-action valve.
3. Detection: Pre-action systems are equipped with fire detection devices, such as smoke detectors or heat detectors, that monitor the protected area for signs of fire.
4. Alarm: When a fire is detected, the pre-action system activates an alarm to alert occupants and initiate emergency response procedures.
5. Pre-action Valve Activation: Upon detection of a fire, the pre-action valve opens, allowing water to flow into the pipes.
6. Sprinkler Activation: Unlike traditional wet systems where each sprinkler head operates independently, in a pre-action system, sprinkler heads are typically held closed by a seal or plug. When a fire causes a sprinkler head to reach its activation temperature, the seal or plug releases, allowing water to discharge from only the affected sprinkler head(s).

By requiring both a fire detection signal and the activation of a sprinkler head, pre-action systems reduce the risk of accidental water discharge while still providing rapid response to a fire event. This two-step process helps prevent water damage in areas where water-sensitive equipment or valuable assets are present. Additionally, pre-action systems can be configured with additional safeguards, such as double interlock systems, to further minimize the risk of inadvertent water release.