How triple-offset geometry eliminates disc-to-seat rubbing, enables metal-seated bubble-tight shut-off, and extends service life in critical applications.
Triple offset (triple eccentric) butterfly valves represent a significant advance over concentric and double-offset designs, enabling bubble-tight metal-seated shut-off suitable for critical isolation applications.
The Three Offsets Explained
- 1**First offset**: Shaft positioned behind the disc face, not through the centreline
- 2**Second offset**: Shaft positioned off the centreline of the valve bore
- 3**Third offset (cone angle offset)**: Disc seat and body seat machined as matching cones, not flat faces
The third offset is the key innovation. By making the seating geometry conical rather than flat, the disc makes contact with the seat only in the final degree of travel — there is zero rubbing during 89° of rotation. This eliminates wear and extends seat life dramatically.
Benefits Over Concentric Designs
- Metal-to-metal seating — no elastomer seat to swell, perish or extrude
- Bi-directional bubble-tight shut-off to ASME Class VI
- Fire-safe rated without separate fire-safe seat design
- Suitable for temperatures from cryogenic (-196°C) to +550°C
- Long service life with no seat wear
Applications
Triple-offset butterfly valves are specified where conventional butterfly valves are inadequate: - Steam isolation in power plants - Natural gas pipeline isolation - Refinery process stream isolation - LNG loading and unloading arms - Cryogenic storage facilities
AIRA's Series 900 triple offset butterfly valves are available from DN100 to DN2000, with pressure ratings to PN 100.
AIRA Euro Automation's engineering team publishes technical guides and application notes based on 30+ years of industrial valve manufacturing experience.
