Tips for Selecting the Right Flange for Butterfly Valve Installation

When installing a butterfly valve, one of the most critical considerations is choosing the correct flange. The compatibility between the butterfly valve and the pipeline flanges ensures tight sealing, smooth operation, and long service life. A poorly selected flange can lead to leakage, excessive torque, or even valve failure. In this article, we will explore the key tips for selecting flanges for butterfly valve installation, including standards, dimensions, and practical recommendations.

1. Understand Butterfly Valve Flange Standards

Butterfly valves are typically designed according to international standards. The matching flanges should comply with the same or compatible standards to ensure proper installation. Common standards include:

• ASME/ANSI B16.5 – Widely used in North America for pipe flanges.

• EN 1092-1 – European standard for steel flanges.

• JIS B2220 – Japanese standard flanges.

• DIN standards – Common in German and European markets.

👉 Tip: Always check the valve manufacturer’s datasheet to verify which flange standards are supported.

2. Pay Attention to Pressure Ratings

Butterfly valve flanges must match the pressure class of the system. If the pipeline operates under PN16 (16 bar) pressure, the flange should be PN16 as well. Mismatched ratings can cause sealing issues or damage.

Common pressure classes include:

• PN6, PN10, PN16, PN25 (metric system)

• Class 150, 300, 600 (imperial/ASME system)

👉 Tip: Never oversimplify by choosing a higher-rated flange. Using a Class 600 flange with a Class 150 butterfly valve may create sealing gaps due to thickness differences.

3. Consider Flange Facing Types

Flange faces determine how the gasket and valve will seal. For butterfly valves, common flange facing types are:

• Raised Face (RF): Most widely used, suitable for general-purpose sealing.

• Flat Face (FF): Often used with cast iron valves to avoid flange stress.

• Ring Type Joint (RTJ): Used in high-pressure or high-temperature services.

👉 Tip: For resilient-seated butterfly valves, flat-face flanges are often recommended to prevent uneven stress on the rubber seat.

4. Account for Inner Diameter Clearance

Butterfly valves have a disc that rotates inside the pipe. If the flange bore (inner diameter) is too small, it may interfere with the valve disc, preventing full opening.

👉 Tip: Always check the valve disc clearance dimensions provided by the manufacturer and confirm that the flange bore is large enough.

5. Material Compatibility

The flange material should match both the valve body and the piping system. For example:

• Carbon steel flanges – Used with carbon steel pipelines in general industries.

• Stainless steel flanges – Suitable for corrosive media such as chemicals or seawater.

• Ductile iron flanges – Cost-effective option for low- to medium-pressure water systems.

👉 Tip: In corrosive environments, using stainless steel or coated flanges will extend service life and reduce maintenance costs.

6. Gasket and Bolting Selection

A flange connection is not only about the valve and flange—it also includes gaskets and bolts. The gasket material must be compatible with the medium (e.g., rubber, PTFE, graphite). The bolt length should allow sufficient tightening without over-stressing the flange.

👉 Tip: For butterfly valves, avoid overly thick gaskets, as they may affect sealing between the valve seat and disc.

7. Practical Installation Recommendations

• Always align the flanges accurately before tightening bolts.

• Use cross-bolting tightening methods to achieve even pressure.

• Avoid welding near the installed butterfly valve to prevent seat damage.

• Perform a pressure test after installation to confirm sealing performance.

Conclusion

Selecting the right flange for butterfly valve installation is crucial for ensuring long-term reliability and safety of the piping system. By carefully checking standards, pressure ratings, flange facing, disc clearance, materials, and gasket compatibility, you can minimize the risk of leakage or valve malfunction.

Whether you are working in water treatment, chemical processing, HVAC systems, or power plants, following these flange selection tips will help achieve a smooth installation and optimal butterfly valve performance.