Concentric Butterfly Valves

Concentric butterfly valves are industrial valves for pipeline on-off switching and flow regulation, widely deployed in petroleum, chemical, metallurgy, hydropower and other industries. Its defining structural feature lies in the coaxial alignment of the stem axis, disc center and valve body center. It boasts easy fabrication and balanced opening/closing torque. The valve stem sits at the geometric center of the body and disc; sealing is accomplished mainly by direct compression of the disc against a rubber seal ring via elastic deformation of the seal.

Flow regulation is realized by rotating the disc 0° to 90° around the stem. Conventional designs suffer from poor temperature resistance of sealing materials and severe abrasion between disc and seat, restricting service to low-pressure and ambient-temperature working conditions. Upgraded high-performance variants combine flexible T-shaped soft sealing rings with laminated stainless steel sheets, alongside high-temperature alloy hardfacing on tapered conical sealing surfaces. Such construction integrates merits of both metal hard sealing and soft sealing; built-in spring assemblies compensate for dimensional tolerances and elastic deformation, enabling service under high temperature, high pressure and bidirectional medium flow. Structurally categorized into concentric-seated and eccentric-seated types, these valves adopt soft seals (EPDM rubber, PTFE etc.) or metal hard seals, with actuation options including manual, electric and pneumatic. Pneumatic concentric butterfly valves powered by compressed air feature compact construction, uniform bidirectional sealing performance and low flow resistance, prevailing in working conditions below 1.6 MPa. Flange concentric alignment is mandatory during installation; periodic opening-closing operation is required for long-term closed service to avoid sticking. Optimized designs have been extended to large-bore specifications, paired with dedicated testing equipment and patented improvements, with part products complying with API 609 standard.

Structural Features and Working Principle

A core characteristic of concentric butterfly valves is coincident centerlines of stem, disc and valve body, delivering simple construction and low manufacturing cost. Lined rubber butterfly valves fall into this category. A primary drawback is persistent squeezing and scraping between disc and seat, resulting in high friction torque and accelerated wear. Main components consist of valve body, disc, stem, seat and actuator. The body is generally integrally cast, while seat sealing rings made of elastic materials such as rubber are embedded inside the body. Mounted centrally, the stem drives the disc to pivot 0°–90° for full opening or closure; the disc is commonly streamlined to minimize flow resistance. Bushings fitted in body end bore holes support and lubricate the valve stem. To mitigate scraping damage and maintain tight shutoff, seats mostly employ elastic rubber or PTFE, yet such elastomeric materials are limited in applicable temperature range — this accounts for the conventional perception that standard butterfly valves cannot withstand high temperatures.

Upon valve closure, the rotating disc compresses the rubber seat and achieves tight shutoff through the seal’s elastic deformation, classified as compression-type soft sealing. For handwheel-operated versions, clockwise or counterclockwise handwheel rotation drives the stem and disc roughly 90° to open or close the valve with effortless manipulation.

Application Scope

Concentric butterfly valves are predominantly specified for pipelines carrying clean water, wastewater, fuel gas and industrial gases, serving as shut-off and throttling components in waterworks, power plants, steel mills, papermaking, chemical, food & beverage and other water supply & drainage systems. Thanks to simple configuration, non-directional sealing limitation, type-I central symmetry with identical bidirectional sealing, low flow resistance and minor operating torque, pneumatic concentric butterfly valves are rated for medium-to-low pressure service and extensively applied in systems under 1.6 MPa.