How to choose concentric or eccentric butterfly valve

Butterfly valves​are divided into four types according to structural differences: Concentric Butterfly Valves, single‑eccentric butterfly valves, double‑eccentric butterfly valves, and triple‑eccentric butterfly valves. Many users are unclear about the concept of eccentricity, as well as when to use concentric, single‑eccentric, double‑eccentric, or triple‑eccentric butterfly valves, so we would like to share a clear explanation.

From concentric to triple‑eccentric butterfly valves​, the opening and closing process becomes increasingly effort‑saving, and the wear on the sealing surfaces is also reduced. By adjusting the axis positions of the valve stem and disc, the sealing performance and opening behavior of the butterfly valve can be modified. Under the same conditions, the operating torque during valve opening is greater than 1, and the angle required for the disc to separate from the seal is less than 1 degree.

The concentric butterfly valve​ is characterized by the valve stem center, disc center, and body center all aligned on the same axis. Generally speaking, the concentric butterfly valve should be used whenever applicable. As a conventional product, it does not demand high sealing performance in terms of structure and operation. To overcome extrusion and scraping issues while ensuring sealing, the seat of a concentric butterfly valve is usually made of elastic materials such as rubber or PTFE, making it a soft‑sealed butterfly valve, which also results in temperature limitations during service.

To solve the problem of contact and compression between the disc and seat in concentric butterfly valves, the single‑eccentric butterfly valve was developed, whose structural feature is that the valve stem axis is offset from the disc center.

The double‑eccentric butterfly valve​ is the most widely used type. It is named so because the valve stem axis is offset from both the disc center and the body center. Many double‑eccentric butterfly valves use line sealing; when closed, friction forms between the disc and the seat, delivering excellent sealing performance. They feature compact dimensions and high pressure resistance. Once opened, the disc quickly disengages from the seat, greatly avoiding excessive extrusion and scraping, reducing operating resistance and wear, and extending the service life of the seat.

The triple‑eccentric butterfly valve​ adds a third eccentricity based on the double‑eccentric structure. Its sealing pair is shaped as an oblique cone rather than a standard cone, mainly adopting short‑stroke force sealing and face sealing. The valve stem features a three‑section design: the two end sections are concentric, while the center section has an offset from the axis of the ends, with the disc mounted on the middle section.

The eccentric structure makes the valve take a double‑eccentric form in the fully open position and a single‑eccentric form in the closed position. Driven by the eccentric shaft, the disc moves inward toward the sealing cone of the seat near closure and fits tightly against the sealing surface to achieve reliable sealing. This resolves the conflict where hard seals offer poor tightness while soft seals seal well but cannot withstand high temperatures.

The selection between concentric, double‑eccentric, and triple‑eccentric butterfly valves mainly depends on usage habits and budget. For non‑extreme working conditions, the concentric butterfly valve is generally preferred and should be used as much as possible due to its simple structure and relatively economical cost.

KEFA VALVE are a professional butterfly valve manufacturer specializing in concentric, single-eccentric, double-eccentric and triple-eccentric butterfly valves. With reliable quality and professional service, we provide suitable valve solutions for various working conditions to meet your different application needs.