Butterfly Valve Disc and Shaft Design

Disc Geometry and Flow Characteristics

The butterfly valve disc is the primary flow control element. Its shape—symmetric, offset, or high-performance—determines flow coefficient, torque characteristics, and shut-off capability.

Types of Disc Designs

• Concentric (centric) disc: simple, low cost, resilient seated, bidirectional

• Single-offset disc: reduces seat wear, used in moderate pressure service

• Double-offset (high-performance): metal seated, higher pressure rating

• Triple-offset disc: true metal-to-metal seal, zero-leakage, bidirectional

Shaft and Stem Construction

• One-piece through shaft for small valves

• Two-piece stub shafts for large valves (reduces flow restriction)

• Keyway or D-flat connection between disc and shaft

• Corrosion-resistant shaft materials: 316 SS, duplex, Inconel in aggressive service

Seat and Disc Interference

Triple-offset butterfly valves achieve tight shut-off through a precisely machined interference fit between disc edge and seat ring. The geometry ensures contact is made as the disc completes its last few degrees of rotation, minimizing friction throughout travel.

High Temperature Applications

Metal-seated butterfly valves handle temperatures from cryogenic to over 600°C. Disc and seat materials are matched for compatible thermal expansion coefficients to maintain sealing performance across operating temperature ranges.