Double Interlock Preaction System

A double interlock preaction system requires two fire conditions before water enters the piping: detection and loss of air or nitrogen pressure caused by sprinkler operation. Choose it when avoiding accidental water release matters more than absolute speed.

What double interlock means

Double interlock means the system needs confirmation from both:

• the detection system, and
• the sprinkler piping side through air or nitrogen pressure loss

Only then does the valve trip and water enter the piping.

When to choose double interlock preaction

Choose it when:

• even a small accidental water release would be unacceptable
• the contents are highly sensitive or valuable
• the owner prefers maximum water control
• the project accepts added complexity in exchange for reduced unwanted discharge risk

Benefits and added value

• Highest protection against accidental water entry into piping
• Strong fit for critical and water-sensitive occupancies
• Useful where leaks, false trips, or accidental discharge would be extremely costly

Tradeoff to understand

Double interlock offers more protection against unwanted water release, but it is more complex and can be slower than single interlock because it needs two confirmed fire conditions.

Best fit examples

• Data centers
• Museums
• Archival storage
• Sensitive manufacturing spaces
• High-value equipment rooms

Related guidance

FireFlex Academy explains that double interlock systems require both detection and pressure loss in the air or nitrogen line before the valve trips.