In a preaction system, the ___________ is opened before the sprinkler heads.

In a preaction system, the preaction valve is a critical component that functions to maintain the integrity of the system until a fire condition is detected. Unlike traditional wet pipe systems, where water is constantly present in the sprinkler piping, a preaction system requires an initial event—such as the activation of a detection system—to open the preaction valve. This valve’s primary role is to allow water into the piping only after the detection of smoke or heat, thus preventing accidental activation of the sprinkler heads.

When the preaction valve opens, it fills the pipes with water. Only after this step will the sprinkler heads activate if a fire is indeed detected, thus limiting accidental discharges due to false alarms or other disturbances. This two-step activation process is vital for protecting sensitive environments, like data centers or museums, where unintended water exposure could cause significant damage. The preaction valve's design aids in creating a controlled response to fire scenarios, enhancing safety in the protected environment.