How pre-action differs
A pre-action system has closed sprinkler heads (like a wet system) but piping is dry until both an independent detection signal and head operation occur. The pre-action valve is held shut by air or nitrogen supervisory pressure.
Single interlock
Valve opens on detection alone, before any sprinkler operates. Used in cold storage (low risk of accidental discharge but freeze risk on wet system).
Double interlock
Valve opens only when BOTH detection signal AND loss of air pressure (from a fused head) occur. Used in data centres, archives, museums — minimises false water release.
Non-interlock
Valve opens on detection OR pressure loss. Faster water delivery; used where speed matters more than discharge protection.
Trade-offs
Pre-action systems are more complex, more expensive, and need more maintenance than wet systems. They also delay water delivery (especially double interlock — sometimes >60 s). Use them only when water sensitivity genuinely justifies the cost.
Bronnen
- NFPA 13 (2022) §8.3
- FM DS 2-0
- APA
- FireTwin AI (2026). Pre-action sprinkler systems (single & double interlock). FireTwin AI. https://firetwin.eu/nl/learn/preaction-systems
- IEEE
- FireTwin AI, "Pre-action sprinkler systems (single & double interlock)," FireTwin AI, 2026. [Online]. Available: https://firetwin.eu/nl/learn/preaction-systems