Preaction Sprinkler Systems Specialized Sprinklers for Tough or Delicate Environments

You may be familiar with Wet Pipe Sprinkler Systems the most common of sprinkler systems where water is always in the pipes ready to go any time a sprinkler head activates or is busted by accident   or Dry Pipe Systems which leaves pipes filled with air which then become filled with water when a sprinkler head activates.  But there is a 3rd very specialized type of sprinkler system called a Preaction Sprinkler .
These types of sprinklers are used in Museums where a sprinkler system could cause major damage were it to go off  by accident or in heavy commercial and industrial applications like large freezers and refrigerated warehouses  where the entire building is the freezer or refrigerator .

In these cases a conventional dry pipe system is not enough because just knocking a head off with a fork lift will cause the freezer to flood  . Thats where Preaction systems fit the bill. Dry air is still used in pipes but only for sensing purposes not to hold water back like a dry system . Water in a Preaction system  is  allowed to flow  by an electric releasing solenoid .

With Preaction systems 2 or 3 actions must take place before they activate and flow water . In a freezer situation both the sprinkler head would have to activate and special heat sensitive Protectowire   sense a fire and melt together or heat detectors activate  to allow the water to flow .

Typical wet system stand pipes on left Preaction system pipes on right

In a museum Protectowire might be  replaced by smoke detectors which would require 2 different smoke detectors  to activate plus a sprinkler head activating before the system allows water to flow.  if any single action happens like break or activation  in Protectowire  or sprinkler head activating the Preaction Panel sends signals to main alarm system  warning the system is ready to activate and requires investigation before the water starts flowing. Once 2nd or 3rd action takes place water is released.


Unlike wet and dry systems which operate by themselves with out assistance of a control panel  Preaction systems require the use of special releasing panels as you see in picture below manufactured by Potter Signal.

Potter releasing panels with Silent knight fire system modules below monitoring relays for water flow ,trouble ,supervisory functions

These panels have special programs which allow various  Preaction scenarios to take place   While some conventional panels can allow  releasing functions as they are known most installers prefer to use dedicated releasing panels made for the purpose such as those made by Potter ,Firelite and others.

You do not see many Preaction systems as dry Systems are preferred due to the costs associated with  Preaction systems initial cost but in the end Preaction system are more cost effective.  I have only seen and worked on a handful of Preaction Systems VS  Dry Pipe Systems .Because of cost issues.

Special compressor which insures as completely as possible dry air enters Preaction pipes