What is the difference between a wet pipe and a dry pipe sprinkler system?

A wet pipe sprinkler system is characterized by being continually filled with water, which means that when a sprinkler head is activated due to heat from a fire, water is immediately discharged from that head. This system is straightforward and effective in environments where freezing is not a concern.

In contrast, a dry pipe sprinkler system is filled with pressurized air or nitrogen, and the pipes contain no water until the system is activated. When a fire occurs and heat activates the sprinkler head, the air pressure drops, allowing the valve to open and water flow into the system and out of the activated sprinkler heads. This design is critical in preventing water from freezing in the pipes, making dry pipe systems suitable for unheated or colder environments.

Understanding the distinction helps in determining the appropriate system for specific conditions, especially in areas susceptible to low temperatures where water in pipes might freeze. Hence, the correct answer highlights the fundamental operational differences between the two systems, clarifying how each functions in fire suppression scenarios.