The principle of the triple-eccentric butterfly valve – simple and easy to understand (with illustrations)

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This post was last edited by Yiding on 2009-12-29 at 22:29. Principle and structure of metal hard seal for U-shaped sealing rings (see Figure 6). Hard-sealed butterfly valves operate on the principle of triple eccentricity: h1 represents the first eccentricity, which is the distance between the rotation center of the valve disc and the sealing surface (see Figure 6); h2 is the second eccentricity, representing the distance between the center of the valve body and the rotation center of the valve stem; h3 is the third eccentricity, which is the angular distance between the center of the valve disc’s sealing surface and the horizontal axis a. This arrangement results in an elliptical conical shape for the valve disc in the normal plane. When the actuator applies torque to rotate the valve stem, the valve disc rotates around center b. The distance from the conical surface passing through the axis of plane a to point b is greater than the radius of the cone, serving as the major axis, while it is less than the radius of the conical surface, serving as the minor axis. When the valve is opened, under the influence of h2, h3, and angles a or β, the elliptical conical sealing surface first separates from the metal U-shaped elastic seat, after which it rotates, thereby reducing the frictional resistance and wear between the valve disc and the seat. When the valve is closed, since it does not rotate around center a, the elliptical conical valve disc, under the effect of eccentricity h2, forms a conical surface at angle β relative to h3a, pressing against the metal U-shaped elastic seat with increasing force. This causes the metal U-shaped elastic seat to undergo elastic deformation (see Figure 7), until the elliptical conical sealing surface of the valve disc fits tightly against the seat, thus achieving reliable sealing.