Differentiate between wet-pipe and dry-pipe sprinkler systems.

• A. Wet-pipe systems keep pipes filled with air, while dry-pipe systems are always filled with water.
• B. Wet-pipe systems release water into pipes when a head is activated; dry-pipe systems release water into pipes when a head is activated but are filled with air.
• C. Wet-pipe systems have water-filled pipes that discharge immediately; dry-pipe systems keep pipes filled with pressurized air or nitrogen and release water into the pipes when a head is activated.
• D. Wet-pipe uses water mist; dry-pipe uses foam.

Answer: (C)

The main distinction is whether the piping itself is normally full of water or kept dry and pressurized with air until a head is activated. In a wet-pipe system, the pipes are always filled with water, so when a sprinkler head is heated and released, water exits immediately into the head and the discharge happens right away. In a dry-pipe system, the main piping is kept dry by filling it with pressurized air or nitrogen; water is stored in a separate reservoir and only released into the dry pipes when a head is activated, letting water push into the lines to reach the sprinkler heads. That difference explains why wet-pipe provides immediate water at the head, while dry-pipe introduces a brief delay as water moves into the dry lines, and also why dry-pipe systems are favored in unheated areas to reduce the risk of freezing.