Dry pipe valves are of a ______ design.

Dry pipe valves are typically of a clapper design. This type of valve incorporates a clapper mechanism that allows for the operation of a dry pipe system, where water is not held within the pipes but is stored in a remote location. The clapper allows air to escape and admits water into the system only when the pressure drops due to an open sprinkler head during a fire event.

This design is essential for preventing water from sitting in the pipes, which can be problematic in areas where freezing might occur. The clapper ensures that the water flows only when needed, maintaining the integrity of the system until activation is required.

Other designs mentioned, such as pneumatic, balloon, and single-action, do not represent the functionality and operation of dry pipe valves effectively and are typically associated with different types of valve systems.