Description

A concentric butterfly valve is a quarter-turn valve in which the disc, stem, and valve body are all aligned on a single central axis. This “zero-offset” design is the simplest and most economical type of butterfly valve. The disc is in constant contact with the elastic seat (usually made of rubber or similar material), which ensures a tight seal. This constant contact, however, generates some friction during actuation. Available in WCB-CF8 cast carbon steel. These valves are suitable for low- and medium-pressure applications, such as water and wastewater treatment plants, HVAC systems, and fire protection systems, where a bubble-tight seal is required.

Types of Check Valves

Although the basic concentric design represents a single typology, these valves are further distinguished by the type of connection at the ends, which determines the method of installation in the pipeline.

• Wafer-Type: Compact, lightweight, and economical design, installed “sandwiched” between two flanges. The flange bolts pass through the valve body holes, holding the valve in place.
• Lug-Type: This design features threaded slots on the valve body, allowing attachment to the pipeline on one side and removal of the line on the other side without compromising the valve installation. It is useful for dead-end service applications.
• Double-Flanged: In this type, the flanges are integrated into both ends of the valve body and are bolted directly to the corresponding pipe flanges. It is often used for large valves.

ASME and API Standards

The design, construction and testing of concentric butterfly valves are governed by several industry standards.

• ASME B16.34: Defines general requirements for the design, materials, and pressure-temperature ratings of valves.
• API 609: This is the primary standard for butterfly valves and covers the design, manufacturing, and testing of both concentric and eccentric designs. It specifies critical dimensions and performance requirements for valves with wafer, lug, and flanged ends.
• API 598: Establishes inspection and testing procedures for valves, including hydrostatic testing of the body and seat, to ensure valve integrity and reliable sealing.
• MSS SP-67: Standard issued by the Manufacturers Standardization Society defining the dimensions, design, testing, and markings of butterfly valves, often complementary to API 609.