A butterfly valve is a type of industrial valve that is used to regulate the flow of liquids and gases. It is a quarter-turn rotary valve that is operated by a handle, lever, or actuator. The valve is designed with a disc-shaped closure element that is mounted on a rod. When the valve is opened, the disc rotates around the rod, allowing the flow of the material through the valve. When the valve is closed, the disc is rotated back to its original position, blocking the flow of the material. Butterfly valves are used in a variety of industrial applications, including oil and gas, water treatment, and chemical processing. They are also used in HVAC systems, and are often used in place of gate valves or globe valves due to their low cost and easy installation. Butterfly valves are also known for their durability and reliability, making them a popular choice for many industrial applications.