Pre-Action Fire Sprinkler Systems employ the basic concept of a “Dry Pipe System” in which Water is not normally contained within the Pipes. The difference, however, is that Water is held within Piping by an Electrically operated Valve, known as a “Pre-Action Valve.” This Valve operation is controlled by independent Detection System.
Two separate events must happen to initiate Sprinkler discharge. First, the Detection System must identify a developing Fire and then open the Pre-Action Valve. This allows water to flow into System Piping, which effectively creates a Wet Pipe Sprinkler System. Second, individual Sprinkler Heads must shatter to permit Water flow onto the Fire.
Unless both the actions are occurred the System will not shower or release Water from the Sprinkler Head.
There are Two types of Pre-Action Systems :
1. Single Interlock System
2. Double Interlock System