What do the terms "wet" and "dry" refer to when discussing fire sprinkler systems?

The term "wet" when discussing fire sprinkler systems specifically refers to systems that are filled with water at all times and are constantly under pressure. This design allows for immediate activation of the sprinklers when a fire is detected, as the water is readily available to discharge through the sprinkler heads.

On the other hand, "dry" systems use air pressure to keep the pipes clear of water until a fire occurs. In dry systems, the pipes are filled with pressurized air, and it is only upon the activation of a sprinkler that a valve opens, allowing water to flow into the pipes and out through the heads. This makes dry systems ideal for environments where freezing could occur, as they minimize the risk of pipes bursting due to ice formation.

Understanding these definitions is crucial for sprinkler fitters, as it impacts system design, installation, and maintenance — ensuring that the right type of system is applied to suit the specific environmental and safety needs of the structure being protected.