Butterfly valves have become a prevalent flow control option across many industries due to their compact design and smooth operation. Within the waterworks sector, butterfly valves find application for main line isolation, throttling, and branch selection. Their versatile usage stems from configurations that suit a variety of installation requirements. Two prominent butterfly valve variations are the center line and eccentric styles, each excelling under certain conditions based on their internal structures.
High Quality Cast Iron Vavles Butterfly Design
At the foundation of a robust butterfly valve design are high quality cast iron materials. Ductile iron remains the predominate choice for valve bodies due its elastic properties that withstand cyclical stresses. Cast iron butterfly valve conforms well to tight radii and complex geometries like those contained within eccentric butterfly valves. Additionally, ASTM A126 Grade B ductile iron possesses sufficient strength for underground applications where compaction pressures can deform lesser metals.
Butterfly Valve Variations – Centerline VS. Eccentric
While the previous post focused on gate valves, it’s also worth reviewing some of the common types of butterfly valves used in similar underground applications. Butterfly valves provide flow isolation using a pivoting disc instead of a gate.
There are two main categories of butterfly valve designs – centerline and eccentric:
In a centerline butterfly valve, the disc rotates about an axis that runs directly through the center of the valve body and disc. This style offers precise sealing along the axis no matter the flow direction.
However, for tight bends or branches in the piping where space is limited, an eccentric butterfly valve can be an option. In an eccentric design, the disc axis is offset above or below the horizontal centerline of the valve body.
For Applications Where Reduced Envelope Is Paramount
Eccentric butterfly valves offset the rotational axis away from center. This inclined orientation shaves wall thickness from the typical butterfly valve shape. Eccentric butterfly valves excels in situations like throttling service, where flow direction remains constant after valve installation. Their truncated form slips into confined chambers such as flow control vaults or meter bypass manifolds. However, the canted disc alignment causes reduced shut-off capability when flow passes through the open valve in both directions. Therefore, eccentric butterfly valves find more specialized usage than center line types.
Turning to valve flowpath variations, center line butterfly valve orient closure members along the symmetrical midline of flow. Advantageously, this center mounted design enables bi-directional shut-off without compromising seal integrity. Center line butterfly valves function effectively as main isolating valves where flow reverses in pumping systems.