A butterfly valve is a compact, lightweight quarter-turn valve that isolates or throttles flow with a rotating disc. It is inexpensive in large sizes and easy to actuate, which is why it is common on water, utility, and large-line service. This guide explains how a butterfly valve works, the main types, and where it fits in oil and gas.
Butterfly Valve in one line: A butterfly valve is a quarter-turn valve with a flat disc mounted on a central shaft in the flow path. Rotating the shaft 90 degrees swings the disc from parallel with the flow (open) to across it (closed). It is compact, light, and cheap in large diameters, and it can both isolate and roughly throttle flow, though the disc always stays in the stream.
The disc sits on a shaft through the center of the valve body. A quarter turn of the shaft rotates the disc edge-on to the flow for the open position and face-on to block it. Because the disc pivots in place rather than being pulled clear of the bore, some obstruction and pressure drop remain even when fully open, but the valve is far shorter and lighter than a gate or globe valve of the same size.
Sealing is made by the disc edge meeting a resilient seat (often elastomer) or, in high-performance versions, an offset (eccentric) disc that cams tightly against a metal or PTFE seat. Quarter-turn operation makes butterfly valves quick to open and easy to fit with a lever, gearbox, or actuator.
A wafer butterfly valve is clamped between two flanges with no bolt holes of its own; a lug design has threaded lugs so it can be bolted to one flange and act as a pipe-end (dead-end) valve. Concentric (rubber-lined) valves suit lower-pressure water and utility service, while double- and triple-offset high-performance butterfly valves handle higher pressures, temperatures, and tighter shutoff for hydrocarbon service.
In oil and gas, butterfly valves are common on large-diameter cooling water, firewater, utility, and tank lines, and high-performance versions serve on process and gas duty where their light weight and low cost in big sizes are advantages. They can throttle to a degree, but a partly open disc is subject to torque and flutter, so precise regulation is left to control valves.
It can throttle roughly, but the disc stays in the flow and experiences torque and flutter at intermediate positions, so it is not ideal for precise control. High-performance butterfly valves handle throttling better, but tight loop control is still the job of a dedicated control valve.
A high-performance butterfly valve uses a double- or triple-offset (eccentric) disc that cams away from the seat during travel and seats tightly at close. That reduces wear and gives tight, reliable shutoff at higher pressures and temperatures than a simple rubber-lined valve.
In large diameters a butterfly valve is much lighter, shorter, and cheaper than a gate valve, and its quarter-turn action is faster and easier to actuate. The trade-off is a disc that stays in the flow, giving more pressure drop than a fully open gate valve.
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