What is a butterfly valve and when is it used?

A butterfly valve uses a rotating disc to control flow. The disc rotates 90 degrees from closed to full open. Characteristics: compact design (short face-to-face), low pressure drop when open, quarter-turn operation, and lower cost than globe valves for larger sizes. Types: concentric (general purpose), high-performance double-offset (better sealing), and triple-offset (zero friction, tight shutoff). Used for larger line sizes (typically 3 inches and above), on-off service, and moderate throttling. Less precise than globe valves for control but economical for large flows.