What is a major difference between a wet pipe system and a dry pipe system?

• A. A wet pipe system holds water in the pipes, while a dry pipe system's pipes are empty until the valve is opened.
• B. A wet pipe system can only be used for water distribution, while a dry pipe system can never be used to distribute water.
• C. Wet pipe systems are most frequently used in commercial applications, while dry pipe systems are most frequently used in residential applications.
• D. A wet pipe system carries wet extinguishing agents, while a dry pipe system contains only dry extinguishing agents.

Answer: (A)

The main idea here is how water is stored and released in the piping network. In a wet-pipe system, the pipes themselves are filled with water at all times, so when a sprinkler head is heated and opens, water flows out immediately. This gives the fastest response but isn’t suitable for unheated or freezing spaces.

In a dry-pipe system, the pipes are kept empty of water and pressurized with air or nitrogen. Water is held back in a separate reservoir and is released into the piping network when a sprinkler head is activated, via a dry-pipe valve. There is a brief delay as the water fills the pipes and reaches the heads, but the system is protected against freezing.

So, the key difference is where water is stored and how it is released: wet-pipe has water in the pipes all the time, while dry-pipe holds water back and fills the pipes after activation.