A dry sprinkler is characterized by which feature?

A dry sprinkler is specifically designed to contain pressurized air or gas instead of water, which is what sets it apart from other types of sprinklers. This feature allows the dry sprinkler system to remain free of water in the pipes until the system is activated, typically by heat from a fire. The seal at the inlet maintains this dry condition by keeping water from flowing into the system until a fire is detected, at which point the seal is broken, allowing water to enter and extinguish the fire.

This design is primarily used in areas where freezing temperatures might cause water in the pipes to freeze, thus preventing the system from functioning properly. By having a seal at the inlet, the system remains reliable and effective, ready to respond to emergencies while ensuring that issues related to frozen water do not occur.