Which sprinkler system requires a two-step release before water reaches the heads?

• A. Wet-pipe
• B. Dry-pipe
• C. Deluge
• D. Pre-action

Answer: (D)

Two-step release before water reaches the heads is a defining feature of a pre-action sprinkler system. In this setup, the pipes are normally dry (or only partially filled), so water cannot reach the heads until two independent actions occur: first, an initiating event such as a detection alarm or a manual release must trigger water into the system (opening the pre-action valve or releasing water from a reservoir), and then a second action—typically a sprinkler head activating by heat or another release—allows water to actually flow through the heads. This extra step helps prevent accidental discharge in sensitive areas. By contrast, wet-pipe systems have water-filled pipes and release water immediately when a head is activated; dry-pipe systems rely on a single valve release to fill the pipes with water, and deluge systems have all heads connected to water and discharge water as soon as the system is triggered.