Which sprinkler system has water in the pipes at all times?

• A. Wet
• B. Multi-cycle
• C. Deluge
• D. Pre-action

Answer: (A)

Water-filled piping at all times is the hallmark of a wet pipe system. In this setup, the pipes themselves are filled with water and each sprinkler head is connected directly to that water-filled network. When a heat-responsive sprinkler activates, water is released immediately through the open head and throughout the system, giving the quickest possible response to a fire.

Dry pipe systems keep air or nitrogen in the pipes and only admit water after the dry-pipe valve is opened, so there’s a short delay before water reaches the heads. Deluge systems have all heads connected to water-filled piping, but all heads are open and flow whenever the system is activated, which changes how water is distributed. Pre-action systems require a non-water-trigger event (like detection or a manual release) before water fills the pipes, adding a delay to discharge.

Multi-cycle isn’t a standard, widely used category for sprinkler piping in most codes, so it doesn’t define water-filled piping the way wet pipe does.