What is preaction sprinkler system?

A sprinkler system employing automatic sprinklers that are attached to a piping system that contains air that might or might not be under pressure, with a supplemental detection system installed in the same areas as the sprinklers.

Preaction systems are typically installed in areas where water damage due to accidental discharge of the sprinklers or breakage of the piping is a concern, or damage in the sprinklers and piping due to freezing. There are three types of preaction systems: non-interlock,single interlock, and double interlock.

non interlock: water flow to sprinklers upon fused sprinkler or detection

single interlock: water flow upon detection

Double interlock: water flow only when detection and sprinklers detect fire