What is one characteristic of a butterfly valve?

A butterfly valve is characterized by its use of a rotating disk to regulate flow through the valve body. This design allows for quick operation, as the disk can be turned a quarter turn (90 degrees) to open or close the valve. The rotational movement of the disk controls the flow of fluid, making it an effective choice for various applications in water distribution systems.

The other options provided do not accurately represent the characteristics of a butterfly valve. For instance, while some valves may not have moving parts, a butterfly valve specifically includes a disk that rotates. Additionally, butterfly valves do not require vertical operation; they can be installed in various orientations. Finally, these valves are versatile and can be used for both liquid and gas applications, rather than being limited to gas flow only.