Butterfly valves are best used on:

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Butterfly valves are best in low pressure, low temperature piping because they combine a compact, lightweight design with simple, quick operation while providing a good shutoff and throttling at modest conditions. The disc rotates 90 degrees to open or close, and in the open position the flow path is relatively direct, which keeps flow resistance reasonable for large-diameter lines. The seal is typically a soft seat against the disc, which works well where pressures and temperatures aren’t extreme. As pressure or temperature rise, the elastomeric seal can deteriorate, extrude, or lose elasticity, leading to leaks or ineffective sealing. For that reason, for high-pressure or high-temperature service, other valve types or metal-seated versions are preferred—even though metal-seated butterfly valves exist, they’re heavier and more expensive. In summary, the combination of cost, size, weight, and reliable performance at modest conditions makes butterfly valves especially suited to low pressure and low temperature piping.