Pre-action systems are similar to dry systems in that the pipes are not filled with water prior to activation of the system. The pre-action valve is keeps the water from flowing through the pipes until it is activated by it's heat or smoke detection elements. Routine maintenance of these systems is essential.

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Pre-action systems are:

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• Less likely to falsely discharge due to the dual action required to activate the system.

• Among the more costly systems to install and maintain, due to their complexity.