Which sprinkler is prevented from allowing water until it operates?

The correct answer is the dry sprinkler. This type of sprinkler is specifically designed to prevent water from being present in the sprinkler piping until it is activated by a fire event. In a dry sprinkler system, the pipes in the system are filled with pressurized air or nitrogen instead of water. When heat from a fire causes the dry sprinkler to activate, the air pressure drops, resulting in the valve opening and allowing water to flow into the sprinkler head. This mechanism is crucial in environments where the temperature can drop below freezing, as it protects the sprinkler system from freezing and potentially bursting.

Upright sprinklers are installed in a way that they can discharge water immediately when activated, making them unsuitable for this characteristic. Corrosion-resistant sprinklers are designed to withstand corrosive environments but do not have the water-holding feature that characterizes dry sprinklers. Check valves, while important in many plumbing systems to prevent backflow, do not relate directly to the operation mechanism of sprinklers but rather to water flow management in piping systems.