Which statement describes the difference between wet-pipe and dry-pipe sprinkler systems?

• A. Wet-pipe systems have water-filled piping; dry-pipe systems have pressurized air until heads are activated.
• B. Both have water-filled piping; the difference is temperature rating.
• C. Wet-pipe systems use foam; dry-pipe uses dry chemical.
• D. Wet-pipe is for residential; dry-pipe for industrial only.

Answer: (A)

The difference being tested is whether the sprinkler piping is filled with water at all times or kept charged with air until a head is activated. In a wet-pipe system, the pipes are full of water from the start, so when a sprinkler head is heated and releases, water flows immediately into the head and out into the area. This gives a fast response but means any leak or break can dump water everywhere, and freezing can be a concern in unheated spaces since water is already in the lines.

In a dry-pipe system, the piping is charged with pressurized air or nitrogen and water is held back by a valve until a head is activated. When a head trips, the valve releases and water rapidly fills the pipes and reaches all heads. This delays water delivery a bit compared to a wet-pipe system, but reduces the risk of accidental water discharge and lowers the chance of freezing in the pipes since they’re normally dry.

The other statements mix up system features that aren’t the fundamental difference here—the distinction is truly about water-filled piping versus air-filled piping until activation.