Flanged Butterfly Valve
Valves / Butterfly ValveA flanged butterfly valve has integral flanges on the body, allowing direct bolted connection to pipeline flanges without relying on through-bolting from adjacent flanges, providing a more robust installation suitable for larger sizes, higher pressures, and applications requiring independent flange connections.
Working Principle
The valve body includes integral flanges cast or forged as part of the body, matching ASME B16.1 (cast iron) or ASME B16.5 (steel) flange dimensions. The disc rotates 90 degrees within the body bore for open/close. Flanged butterfly valves are commonly used in larger sizes (NPS 12 and above) where the wafer body would lack sufficient structural rigidity. The flanged design allows each end of the valve to be independently bolted to its adjacent flange, making it suitable for dead-end service and applications where one side may be disconnected. The resilient seat liner is the same as in wafer and lug designs (EPDM, NBR, Viton, or PTFE).
Key Components
Body with integral flanges, resilient seat liner, disc, shaft, bearings, packing, handwheel or gear operator (large sizes), flange gaskets.
Types & Variants
| Type | Key Feature | Typical Use |
|---|---|---|
| Cast iron flanged | Cast iron body, Class 125/150 flanges | Water distribution, HVAC large sizes |
| Ductile iron flanged | Ductile iron body, Class 150 flanges | Water and wastewater treatment |
| Steel flanged | Carbon steel body, Class 150-300 flanges | Process plant, moderate pressure |
| Flanged lined | PTFE-lined body with flanges | Chemical service, corrosive fluids |
Common Materials
Body: cast iron (ASTM A126), ductile iron (ASTM A395), carbon steel (ASTM A216 WCB), or stainless (ASTM A351 CF8M). Seat: EPDM, NBR, Viton, or PTFE. Disc: ductile iron, aluminum bronze, 316SS. Shaft: 416SS or 316SS. Flanges per ASME B16.1 (CI/DI) or B16.5 (steel).
Applicable Standards
- API 609 (butterfly valves)
- MSS SP-67 (butterfly valves)
- AWWA C504 (rubber-seated, waterworks)
- ASME B16.1 (CI/DI flanges)
- ASME B16.5 (steel flanges)
Industrial Applications
- Municipal water distribution (large sizes)
- Wastewater treatment plant isolation
- HVAC large-diameter water systems
- Power plant cooling water
- Industrial process isolation (moderate pressure)
- Fire protection main isolation
Advantages & Disadvantages
Advantages
- Independent flange connections — each end bolts to its own flange
- Suitable for dead-end service (one flange removed under pressure)
- More robust than wafer for large sizes and heavy-duty applications
- Easy to install with standard flange gaskets
- Can be removed from one side without disturbing the other
Disadvantages
- Heavier and longer face-to-face than wafer or lug designs
- Higher cost than wafer due to flanged body
- Flange gaskets add potential leak points
- Requires more installation space
- Flange bolt holes must align with pipeline flanges
Selection Guide
- Flanged butterfly valves are preferred for NPS 12 and above where wafer bodies lack structural rigidity
- For dead-end service, flanged or lug-style is required — wafer is NOT acceptable
- Use flat-face flanges with cast iron bodies and full-face gaskets to prevent cracking the body
- For raised-face flanges with steel bodies, spiral wound gaskets are standard
- Gear operators are recommended for NPS 10 and above due to increasing operating torque
Practical Tips
- Flanged butterfly valves in municipal water systems are often installed with only half the flange bolts because installers skip every other bolt — this causes seat deformation and leakage. Install ALL bolts per the manufacturer's torque specification
- For large-diameter flanged butterfly valves (NPS 24+), specify a support base to prevent the valve from sagging under its own weight and misaligning the disc
FAQ
When should I use flanged instead of wafer?
Use flanged when: (1) the valve is NPS 12 or larger, (2) dead-end service is required, (3) one side may be disconnected while the other is under pressure, (4) the installation requires independent flange connections, or (5) structural rigidity is a concern.
What gasket is needed for a flanged butterfly valve?
Cast iron bodies with flat-face flanges use full-face rubber or compressed fiber gaskets. Steel bodies with raised-face flanges use spiral wound gaskets (graphite/stainless) per ASME B16.20. Never use a ring joint gasket with a butterfly valve — there is no groove in the body.