What do preaction non-interlock, preaction single interlock, and preaction double interlock mean, and when should I choose each one?

What Each Option Means

Preaction non-interlock

A non-interlock preaction system opens when either detection operates or air pressure is lost from the sprinkler piping. In practice, this means the system can act like a dry system if a sprinkler opens before the detection release happens.

Choose it when:

• You want faster operation than stricter interlocked designs
• The space still needs preaction logic, but not the highest level of anti-accidental-water protection
• Moderate water sensitivity is acceptable

Preaction single interlock

A single interlock preaction system requires one detection event before water enters the sprinkler piping. Once the detection condition is met, the piping fills, and water discharges if a sprinkler opens.

Choose it when:

• You want better protection against accidental water entry than non-interlock
• You still want relatively quick fire response
• The space contains equipment or contents that are water-sensitive, but not the most critical

Preaction double interlock

A double interlock preaction system requires two events:

1. Fire detection must operate, and
2. Air pressure must drop, usually because a sprinkler has opened

Water does not enter the sprinkler piping until both conditions happen.

Choose it when:

• The space is highly water-sensitive
• You want maximum protection against accidental water entering the piping
• You are protecting data rooms, museums, archives, freezers, or similar critical areas

How to Decide Quickly

• Need the fastest, least restrictive preaction logic? Choose non-interlock
• Need balanced protection and performance? Choose single interlock
• Need the highest safeguard against unintended water entry? Choose double interlock

Good to Know

Double interlock is often preferred where even one unwanted water event could cause major downtime or damage.