What is the purpose of a butterfly valve and where is it commonly used?

• A. To vent air from tanks.
• B. To measure flow rate in piping.
• C. To allow gradual flow control in small piping.
• D. To provide a tight shutoff in large-diameter piping; used for isolation where full shutoff is needed.

Answer: (D)

Butterfly valves are designed to provide a tight shutoff and isolation in large-diameter piping. The disk sits in the center of the pipe and, with a 90-degree turn of the stem, the valve goes from fully open to fully closed. This compact design yields a reliable seal for complete isolation when maintenance or safety procedures require it, while keeping a low pressure drop when fully open. They’re not primarily for venting air, measuring flow, or precise throttling in small pipes; other devices handle those tasks better. So their main use—full shutoff and isolation in large-diameter systems—explains why this option is the best fit.