If you've started looking into butterfly valves, you've likely encountered two key terms: concentric and eccentric. While they may look similar at first glance, the geometric difference between these designs is profound, directly impacting the valve's performance, lifespan, and suitability for specific applications. Understanding this difference is the key to selecting a valve that not only works but excels.
This post will break down the design of both concentric and eccentric butterfly valves, so you can confidently choose the right one for your system.
(First time learning about these valves? We recommend reading our complete guide to butterfly valves for a primer.)
The concentric design is the most basic and common type of butterfly valve. It's often called a "zero offset" valve because the stem is centered in the disc, which is in turn centered in the pipe's bore.
In this design, the valve relies entirely on the resilience of its soft rubber or polymer seat for sealing. As the disc rotates, it stays in constant contact with the seat. This means there is friction between the disc edge and the seat throughout the entire 90-degree rotation.
An eccentric butterfly valve features one or more "offsets," which are intentional shifts in the geometry of the valve's internals. These offsets are engineered to solve the primary drawback of the concentric design: friction-induced wear.
The double offset design is the industry standard for what is often called a "high-performance butterfly valve." It incorporates two distinct offsets:
This clever geometry creates a "cam action." As the valve opens, the disc immediately lifts off the seat. The disc only makes contact with the seat in the final few degrees of closing. This action drastically reduces friction, which minimizes wear and extends the valve's service life.
The triple offset valve takes performance to the highest level, making it suitable for the most critical and demanding applications. It includes the two offsets of the double offset design, plus a third:
This final offset completely eliminates all friction during operation. The disc and seat engage perfectly, forming a bubble-tight, metal-to-metal seal without any rubbing.
| Feature | Concentric (Zero Offset) | Eccentric (Double & Triple Offset) |
|---|---|---|
| Sealing Mechanism | Disc compresses soft seat | Cam-action rotation, precise disc/seat contact |
| Friction | High and constant | Very low to non-existent |
| Pressure Ability | Lower pressures | Higher pressures and temperatures |
| Service Life | Good (limited by seat wear) | Excellent to superior |
| Cost | Lower initial cost | Higher initial cost |
| Typical Use | General service, utilities, water | Critical service, steam, chemicals, oil & gas |
Your application will dictate the best choice:
Choose a Concentric Valve if: Your primary driver is cost, your system operates at a lower pressure, the fluid is clean (non-abrasive), and you need a reliable, general-purpose shutoff valve.
Choose an Eccentric Valve if: Your system involves high pressures or temperatures, you need to minimize seat wear for a longer service life, the media is abrasive, or the application is critical and demands the utmost reliability.
While a concentric butterfly valve is an excellent and economical choice for a wide range of everyday applications, eccentric designs provide the enhanced durability and performance required for more demanding industrial environments. By understanding the fundamental differences in their design, you can improve your system's reliability and lower its total cost of ownership over time.
Explore our full range of Butterfly Valves, or contact our technical team for expert assistance with your specific application.
