Triple Offset vs Concentric Butterfly Valves: When to Use Each
Understanding the differences between triple offset and concentric butterfly valves is critical for selecting the right valve for your application. This guide breaks down when each design excels.
What Is a Concentric Butterfly Valve?
A concentric (or centric) butterfly valve has its stem passing through the centre of the disc, which sits in the centre of the pipe bore. The disc rotates against the seat through the full 90° of travel, creating a seal through interference fit between the elastomer seat and the disc edge. This is the most common and cost-effective butterfly valve design, suitable for general-purpose isolation and throttling in low-to-medium pressure applications. TTV concentric valves are available in soft-seated (EPDM, NBR, Silicone, Viton) and PTFE-seated variants, covering temperatures from -40°C to 200°C and sizes from DN32 to DN3000.
What Is a Triple Offset (Triple Eccentric) Butterfly Valve?
A triple offset butterfly valve features three distinct offsets: the shaft is offset from the disc centre (first offset), offset from the pipe centre (second offset), and the seat cone angle is offset from the pipe axis (third offset). This geometry means the disc lifts completely off the seat after just a few degrees of rotation, eliminating friction and wear during operation. The result is a metal-to-metal or R-PTFE seal capable of Class VI (zero leakage) tightness, fire-safe performance, and bidirectional sealing. The TTV Colossus range delivers this performance in sizes from DN40 to DN600.
When to Choose Concentric
Choose concentric butterfly valves for general water service, HVAC, low-pressure chemical lines, food and beverage processing, and applications where temperature stays below 200°C and pressure below PN16. They offer the best value for non-critical isolation and throttling duties. The soft seat provides bubble-tight shutoff at a fraction of the cost of a triple offset design.
When to Choose Triple Offset
Choose triple offset butterfly valves for high-pressure applications (PN25, Class 150/300), high-temperature service (up to 360°C with metal seat), hydrocarbon and fire-safe requirements, steam isolation, and any application requiring Class VI tightness or bidirectional zero-leakage sealing. The higher upfront cost is justified by longer service life, lower torque, and zero-maintenance sealing in demanding conditions.
Quick Comparison Table
Concentric: Pressure up to PN16, Temperature -40°C to 200°C, Seat elastomer or PTFE, Tightness bubble-tight, Cost lower, Best for general service. Triple Offset: Pressure up to Class 300, Temperature -50°C to 360°C, Seat R-PTFE or metal, Tightness Class VI zero-leakage, Cost higher, Best for critical/high-performance service.