Which sprinkler system contains water in the system at all times?

• A. Wet pipe
• B. Dry pipe
• C. Deluge
• D. Deluge-wet

Answer: (A)

Water is kept in the piping of this system all the time, so it can respond immediately when a sprinkler head is activated. In a wet pipe system, the network is permanently charged with water, which means the moment heat opens a head, water flows out instantly to help control the fire. This quick response is the defining feature of wet pipe systems.

Dry pipe systems, by contrast, keep the pipes filled with pressurized air or nitrogen and hold back the water with a valve; once the system is triggered, the valve opens and water must fill the pipes, causing a delay before water reaches the sprinklers. Deluge systems have all heads open and are typically not filled with water until activation, so water is released to all heads at once after the system is activated. Deluge-wet is a hybrid design not characterized by water being present in all piping at all times.