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    What is a double eccentric butterfly valve

    Posted by Bundor valve
    In this article, Bundor Valve will talk to you about double eccentric butterfly valve. When it comes to double eccentric butterfly valve, we must talk about this double eccentric structure.

    The so-called double eccentricity, the first eccentricity means that the valve stem axis deviates from the center of the sealing surface, that is, the valve stem axis is behind the disc surface. This eccentricity makes the contact surface of the butterfly plate and the valve seat both the sealing surface, which fundamentally overcomes the inherent deficiencies of the concentric butterfly valve, thereby eliminating the possibility of internal leakage at the upper and lower intersections between the stem shaft and the sealing valve seat.
    The other eccentricity means that the center of the water passage hole of the valve body is offset from the left and right of the valve stem axis, that is, the valve stem axis divides the butterfly plate into two parts with one more side and one less part. This kind of eccentricity can make the butterfly plate quickly disengage or approach the valve seat during the opening and closing process, reduce the stroke friction between the butterfly plate and the sealing valve seat, reduce wear, reduce the opening and closing torque, and prolong the service life of the valve seat.
    The outer circumference of the disc and the sealing valve seat of the double eccentric butterfly valve are processed into a hemispherical surface, and the outer spherical surface of the disc is squeezed by the inner spherical surface of the sealing valve seat to produce elastic deformation to achieve the purpose of closing. Double eccentric butterfly valve usually uses PTFE material as its sealing valve seat, and can also use metal sealing valve seat to expand its application in high temperature field. However, the sealing of the double eccentric butterfly valve with metal sealing seat is still a position sealing structure, that is, the sealing surface of the butterfly plate and the valve seat is in line contact, so it can not withstand high pressure, and it will inevitably lead to large leakage when used in a high pressure system. Therefore, in high pressure or systems requiring tight shut-off, the use of double-eccentric butterfly valves with metal-sealed valve seats should be avoided as much as possible.