Quick Answer
The article compares double-flanged and lug-type butterfly valves, focusing on installation, pressure handling, sizing, and maintenance. Double-flanged valves suit high-pressure, large-diameter, permanent installations, while lug-type valves are lighter, cheaper, and ideal for dead-end service or frequent maintenance. Selection depends on pressure ratings, pipeline size, and project budget.
Different types of valves are needed in your system for different reasons. The distinction between a lug valve and a flanged valve depends on how they are installed.
When selecting a double-flanged butterfly valve or a lug valve, consider key long-term expenses. You must evaluate both upfront installation costs and future maintenance expenses.
This article compares both types across installation, pressure handling, sizing, and application fit.
What Is a Double-Flanged Butterfly Valve?
A double flanged or double eccentric valve features integral flanges at both ends. These bolt directly to adjacent pipeline flanges.
There is a rotating disc along an axis that regulates the flow of fluid. The pressure is distributed uniformly over the whole disc because of the flanges.
The body is usually made of ductile iron, WCB cast steel, and stainless steel. Double-flanged butterfly valve manufacturers produce these valves to ANSI, DIN, API, and JIS dimensional standards.
What Makes the Single Flange Butterfly Valve Different?
This design differs from a single-flange butterfly valve (wafer type). A wafer valve has no integral flange. It relies on adjacent pipe flanges for compression instead.
No through-bolts are required. One side of the pipeline can be unbolted and removed without disturbing the other. This makes lug-type valves suitable for dead-end service.
Seat materials include EPDM and PTFE, which handle corrosive or chemically active media. Ductile iron, WCB, and stainless steel are the body materials, which are similar to the double-flanged type.
Typical size range runs from DN50 (2″) to DN600 (24″). Lug valves weigh less than double flanged equivalents of the same bore.
Key Structural Differences at a Glance
The table below summarizes the critical structural and operational differences.
| Feature | Double Eccentric Butterfly Valve | Lug Type Butterfly Valve |
| Connection method | Integral flanges bolt to both pipe flanges | Threaded lugs bolt independently to each flange |
| Dead-end service | Not recommended without modification | Yes, one side can be isolated |
| Body weight | Heavier, larger face-to-face dimension | Lighter, more compact profile |
| Bolting pattern | Double flanged butterfly valve bolting: full stud bolt set through both flanges | Separate bolts into each lug, no through-bolts needed |
| Standards | ANSI, DIN, API, JIS. See the double flanged butterfly valve dimensions in the product double flanged butterfly valve catalogue | The same standards apply; a shorter face-to-face dimension |
Pressure Ratings: Which Valve Handles More?
Pressure performance is often the deciding factor between these two valve types. Engineers must verify ratings before finalizing specifications.
Double flanged valve designs sustain higher mechanical stress because the integral flanges distribute load uniformly across the full face. This improves sealing consistency under high-pressure conditions.
These valves suit high-pressure, high-temperature, and corrosive service. Common applications include oil and gas transmission, large-diameter water mains, and power generation.
Lug-type valves perform well in low-to-medium-pressure service. Pressure ratings can decrease when used in dead-end applications. Always verify rated pressure against actual system conditions.
For pipeline diameters above DN400, the double eccentric butterfly valve provides greater structural stability. Review the double-flanged butterfly valve PDF from your supplier for pressure-temperature derating tables.
Double-Flanged Butterfly Valve Sizes, Dimensions, and Bolting
Buyers should always confirm sizing and evaluate the certified double-flanged butterfly valve catalogue before ordering. This helps prevent costly mismatches during procurement.
Double-flanged butterfly valve sizes typically range from DN50 (2″) to DN2000 (80″) for large infrastructure projects.
Face-to-face dimensions follow ANSI B16.10, EN 558 Series 13/14, or API standards. Double-flanged butterfly valve dimensions vary by pressure class and nominal bore. A double-flanged butterfly valve PDF datasheet from your supplier provides the full dimensional table.
For quick reference, ANSI face-to-face examples include:
- DN80 (3″): approx. 216 mm (8.5″)
- DN150 (6″): approx. 368 mm (14.5″)
- DN200 (8″): approx. 444 mm (17.5″)
Double-flanged butterfly valve bolting requires stud bolts and nuts to secure both flanges simultaneously. The bolt circle diameter, bolt count, and bolt size follow the applicable standards of ANSI Class 150/300 or PN10/PN16.
Lug-type valves use shorter, separate bolts that thread into each lug. Fewer bolts mean faster disassembly during maintenance.
Installation and Maintenance Comparison
The total project cost is determined by how easily a valve can be installed. Both valve types require different approaches to site preparation and maintenance planning.
Installing a double-flanged valve type requires precise flange alignment on both sides before torquing the full bolt set. The result is a rigid, leak-proof assembly built for permanent service.
Lug-type valves bolt independently to each flange. Teams can remove downstream piping without disrupting upstream pressure. This simplifies systems requiring frequent component replacement.
From a cost perspective, lug-type valves carry lower unit cost and weigh less. The double flanged valve commands a higher price but delivers consistent performance in demanding, long-cycle service.
Which Valve Type Fits Your System?
Selection between two valve types depends on specific application conditions.
The checklist below helps project teams make a confident, spec-ready decision.
Choose a double-flanged valve when:
- Operating pressure or temperature exceeds the lug type’s rated range.
- Pipeline diameter is DN400 or larger, such as water infrastructure or oil and gas transmission lines.
- Installation is permanent, and maintenance access is infrequent.
- Project specs require documented double-flanged butterfly valve dimensions per ANSI, DIN, or API standards.
Choose a lug-type butterfly valve when:
- Frequent maintenance, inspection, or valve replacement is required.
- Dead-end or end-of-line isolation is a system requirement.
- Budget or weight constraints apply, especially for smaller-bore, moderate-pressure applications.
- The system environment includes HVAC, light industrial, chemical processing, or water treatment.
Conclusion
Choosing between a double-flanged butterfly valve and a lug type comes down to four key factors. You must evaluate the pressure rating, installation type, maintenance frequency, and dimensional compliance.
High-pressure, large-diameter, and permanent installations call for the double-flanged design. Budget-conscious, maintenance-intensive, or dead-end service applications call for the lug type.
Xintai Valves has manufactured industrial butterfly valves since 1998. Products comply with ISO 9001, API, CE, ANSI, DIN, JIS, and BS standards. The company operates six production bases across China, with a 58,000 sqm workshop and an annual output of over 270,000 valves.
We also supply engineering firms, project buyers, and distributors across nearly 40 countries. Clients include major operators in North America, South America, Europe, and the Middle East.
