Butterfly valves are quarter-turn valves that regulate the flow of fluids through pipelines. A circular disk or vane is fixed on a central shaft and spins to enable or restrict fluid flow. When the valve opens, the disc is parallel to the flow direction, allowing fluid to pass through. When the valve is closed, the disc rotates perpendicular to the flow direction, preventing the flow entirely. Butterfly valves are widely employed in applications that need fast and effective flow control, such as water treatment, HVAC systems, and chemical processing. They have advantages such as small size, minimal pressure drop, and ease of operation, making them adaptable solutions for various industries.

Butterfly valves seal using the fluid's pressure to form a tight seal between the disc (or vane) and the valve seat. When the valve is closed, the disc rotates perpendicular to the flow direction, pressing against the seat to produce a seal. The seat and disc are designed so that the sealing surfaces make complete contact, avoiding fluid leakage. Furthermore, certain butterfly valves may have a robust seat composed of rubber or elastomers, which provides a tighter seal and compensates for any flaws in the sealing surfaces. This design enables butterfly valves to provide dependable shutdown capabilities in various applications.