The Key Components of the Concentric Butterfly Valve

Understanding the key components of a concentric butterfly valve is essential for proper selection and maintenance. The concentric butterfly valve, also known as a centric or resilient-seated butterfly valve, features a symmetrical design where the stem passes through the center of the disc and the disc is centered within the seat bore. This article provides a comprehensive overview of each major component.

Valve Body

The body is the main pressure-containing component, typically manufactured from cast iron (ASTM A126), ductile iron (ASTM A536), carbon steel (ASTM A216 WCB), or stainless steel (ASTM A351 CF8M). The body type may be wafer, lug, or double-flanged, depending on the installation requirements. Wafer bodies are the most compact and economical, while lug bodies allow end-of-line service and double-flanged bodies provide the most robust connection.

Disc

The disc is the flow-controlling element that rotates 90° between the open and closed positions. In a concentric butterfly valve, the disc is centered in the bore and makes uniform contact with the seat around its full circumference. Common disc materials include ductile iron, stainless steel (CF8, CF8M), aluminum bronze, and special alloys for corrosive service. The disc profile is typically a lens or flat shape, optimized for low torque and good flow characteristics.

Seat

The seat provides the sealing interface between the disc and body. In resilient-seated designs, the seat is molded from elastomers such as EPDM, NBR, FKM, or PTFE. The seat may be a cartridge type (replaceable without removing the valve), bonded type, or press-fit type. The seat material determines the valve's temperature range, chemical compatibility, and sealing performance.

Stem (Shaft)

The stem transmits the torque from the actuator to the disc. Most concentric butterfly valves use a one-piece or two-piece stem design. The stem passes through the disc and is supported by bearings in the body. Common stem materials include stainless steel grades 410, 416, 420, 431, and 316. The stem-to-disc connection may use pins, keys, or a square/hex drive.

Actuator

The actuator provides the force to rotate the disc. Options include manual lever (for smaller sizes), gear operator (for larger sizes or higher pressures), pneumatic actuator, and electric actuator. The ISO 5211 mounting pad on the valve body allows direct mounting of actuators without additional brackets, simplifying installation and reducing costs.