Quick Answer
A butterfly valve is a quarter-turn valve with a rotating disc that controls flow. It is compact, lightweight, and inexpensive in large sizes, making it the most common valve for large-diameter water, HVAC, and process isolation. Main types: wafer, lug, and double/triple-offset designs for higher-pressure and metal-seated service.
How a Butterfly Valve Works
A disc is mounted on a stem in the center of the pipe. Rotating the handle or actuator 90 degrees turns the disc from parallel to flow (open) to perpendicular (closed). The disc is always in the flow path, so butterfly valves have a moderate pressure drop even when fully open.
Main components
- Body — wafer, lug, or flanged
- Disc — the closing element
- Stem/shaft — connects disc to operator
- Seat — elastomer (resilient) or metal
- Operator — lever, gearbox, or actuator
Types of Butterfly Valves
| Type | Seat | Typical Use |
|---|---|---|
| Resilient-seated (concentric) | Elastomer | Water, HVAC, low pressure |
| Double-offset | Metal or soft | Higher pressure, partial throttling |
| Triple-offset | Metal | High pressure, high temp, bubble-tight metal seal |
Advantages and Limitations
Advantages: compact, light, low cost in large sizes, fast quarter-turn operation, low maintenance. Limitations: the disc obstructs flow (higher pressure drop than a full-bore ball valve), sealing is less bubble-tight in some designs, and throttling should be avoided in resilient-seated types to prevent seat wear.
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Common Applications
- Water distribution and wastewater
- HVAC and chilled water systems
- Fire protection systems
- Large-diameter gas and process lines
Frequently Asked Questions
What is the difference between a butterfly valve and a ball valve?
Both are quarter-turn, but a ball valve has a straight-through bore (lower pressure drop, better shut-off), while a butterfly valve uses a disc that stays in the flow path (more compact and cheaper in large sizes).
Are butterfly valves good for throttling?
Partially. Metal-seated and triple-offset types can throttle; resilient-seated types should only be used for on/off to protect the elastomer seat.
What sizes are butterfly valves available in?
Typically 2″ to 96″, with 12″+ being the most economical choice for large pipelines.
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Disclaimer: This article is provided for general educational and informational purposes only and does not constitute professional engineering advice. Valve applications vary with pressure, temperature, media, and applicable codes. Always verify specifications against the manufacturer’s data sheet and consult a qualified engineer before selecting, installing, or repairing any valve. Valve Knowledge Hub makes no warranties about the accuracy or completeness of the information on this site and assumes no liability for any use of it.