Butterfly Valve Types: Concentric, High-Performance and Triple-Offset — Complete Selection Guide

Butterfly valves are quarter-turn valves that use a rotating disc as the closing element. They are compact, lightweight, and cost-effective compared to gate or ball valves at large diameters, making them the preferred choice for sizes above DN100 (4") in many applications. However, not all butterfly valves are equal — the three main designs have very different performance characteristics, pressure ratings, and application suitability.

Type 1: Concentric (Resilient-Seated) Butterfly Valves

The concentric butterfly valve has the disc stem aligned with the centreline of the disc and the pipe bore. The disc seats against an elastomeric (rubber or EPDM) seat bonded into the valve body. This design is the most economical but has significant limitations:

• The disc rubs against the seat throughout the full rotation — causing seat wear in high-cycle applications
• Unsuitable for temperatures above 120°C (EPDM seat limitation)
• Pressure rating limited to ANSI Class 150 / PN16 (typically 16 bar at 20°C)
• Not suitable for slurry or abrasive service (seat abrasion)
• Not fire-safe

Applications: Water supply, irrigation, cooling water, HVAC heating and chilled water, wastewater, fire protection (FM-approved). Standards: EN 593, AWWA C504, MSS SP-67.

Type 2: Double-Eccentric (High-Performance) Butterfly Valves

The double-eccentric (or double-offset) butterfly valve has two offsets from the disc centreline: the stem is offset laterally from the disc centreline (first eccentricity), AND offset from the pipe centreline (second eccentricity). This causes the disc to cam away from the seat immediately as it begins to open, eliminating the sliding contact problem of concentric designs.

This design offers significantly improved performance:

• Longer seat life due to near-zero rubbing contact on opening and closing
• Suitable for higher pressures — up to ANSI Class 300 / PN50 (depending on size and manufacturer)
• Wider temperature range with graphite seat designs — up to 425°C
• Available in fire-safe designs to API 607
• Can use flexible metal seats or graphite seats for higher temperature service

Applications: Oil and gas (upstream and midstream), power generation, chemical processing, steam service up to moderate pressures, HVAC for larger systems. Standards: API 609 Category A, EN 593.

Type 3: Triple-Offset (Triple-Eccentric) Butterfly Valves

The triple-offset butterfly valve adds a third eccentricity: the seating surface geometry is a cone (right-angle cone), not a cylinder. This means the disc makes contact with the seat only at the very final point of closure — there is zero rubbing contact throughout the entire stroke. Only when the valve is fully closed does the seating surface contact the seat ring, creating an interference fit that produces a metal-to-metal bubble-tight seal.

This makes triple-offset butterfly valves the highest-performance butterfly valve available:

• Bubble-tight Class VI shut-off (equivalent to ball valve sealing performance)
• Pressure rating up to ANSI Class 2500 (depending on size)
• Temperature range from -196°C (cryogenic) to +650°C (high-temperature service)
• Fire-safe by design — metal-to-metal seating is inherently fire-safe
• Bidirectional sealing capability
• Suitable for high-pressure steam, LNG, hydrocarbon gas, and critical isolation service
• Zero seat wear — the seat is a separate replaceable ring, not bonded to the body

Applications: Offshore and subsea, refinery and petrochemical isolation, power plant main steam and feedwater isolation, LNG terminals, high-pressure gas pipelines. Standards: API 609 Category B, ASME B16.34, EN 593.

Comparison Table

Selecting the Right Butterfly Valve

• Water, HVAC, irrigation (max 120°C, max 16 bar): Concentric resilient-seated
• Oil and gas, moderate pressure steam, chemical (up to Class 300): Double-eccentric (HPBV)
• Critical isolation, high-pressure steam, LNG, offshore (up to Class 2500): Triple-offset
• Any hydrocarbon service requiring fire safety: Double-eccentric (API 607) or triple-offset
• Cryogenic service (LNG, liquid nitrogen): Triple-offset with cryogenic extended bonnet