How Does a Butterfly Valve Work?
How Does a Butterfly Valve Work?
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A butterfly valve is a quarter-turn rotary valve used to start, stop, or regulate fluid flow in pipelines. It consists of a rotating disc mounted on a central shaft, which controls flow by turning perpendicular (closed) or parallel (open) to the flow direction.
1. Key Components
| Part | Function |
|---|---|
| Body | Houses the disc and connects to the pipeline (wafer, lug, or flanged). |
| Disc | Rotates 90° to open/close flow (also called the “butterfly”). |
| Stem | Transmits torque from the actuator to the disc. |
| Seat | Provides a tight seal (rubber, PTFE, or metal). |
| Actuator | Manual (lever, gear) or automated (pneumatic, electric, hydraulic). |
2. Working Principle
A. Open Position (0°)
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The disc is parallel to the flow, allowing full fluid passage.
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Minimal pressure drop (ideal for low-resistance systems).
B. Partially Open (0°–90°)
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The disc is angled, regulating flow rate (used for throttling).
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Higher turbulence than gate/ball valves (not ideal for precise control).
C. Closed Position (90°)
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The disc is perpendicular to the flow, blocking it completely.
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The seat compresses against the disc for a bubble-tight seal (if elastomeric).
3. Types of Butterfly Valves
| Type | Design | Best For |
|---|---|---|
| Wafer | Lightweight, clamped between flanges | Low-pressure water/air |
| Lug | Threaded inserts for bolt-on installation | Dead-end service, easy maintenance |
| Flanged | Integral flanges for direct piping connection | High-pressure systems |
| Double Offset | Eccentric stem reduces seat wear | HVAC, moderate pressures |
| Triple Offset | Metal seat, zero leakage | Oil & gas, high-P/temp |
4. Advantages & Disadvantages
✔ Advantages
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Compact & lightweight vs. gate/ball valves.
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Fast operation (90° turn).
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Lower cost for large diameters.
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Good flow regulation (if designed for throttling).
✖ Disadvantages
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Higher pressure drop than gate/globe valves.
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Not ideal for slurries (disc can erode).
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Limited high-P/temp (unless triple-offset design).
5. Common Applications
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Water Treatment: Pump control, filtration.
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HVAC: Chilled water, air handling.
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Oil & Gas: Tank vents, low-P pipelines.
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Chemical Processing: Corrosive fluids (with lined seats).
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Marine/Shipbuilding: Seawater ballast systems.
6. Butterfly Valve vs. Other Valves
| Valve Type | Best For | Butterfly Valve Comparison |
|---|---|---|
| Gate Valve | On/off, high-pressure | Heavier, slower, no throttling |
| Ball Valve | Tight shutoff, high-P | More expensive, better sealing |
| Globe Valve | Precise throttling | Higher pressure drop |
Conclusion
A butterfly valve is a versatile, cost-effective choice for quick shutoff or moderate throttling in large pipes. For high-pressure/temperature or zero-leakage needs, consider triple-offset metal-seated designs.
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