Structure and Performance of Soft Seals in Butterfly Valves
Jun 11, 2021
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A butterfly valve is widely used as the best device to cut off or adjust the flow on the medium pipeline in urban construction, petrochemical, metallurgy, electric power and other industries. The butterfly valve structure itself is the most ideal opening and closing part in the pipeline, and it is the development direction of pipeline opening and closing parts nowadays.
First of all, the soft sealing butterfly valve with a single eccentric structure, in which the sealing section of the valve seat or the bisector in the thickness direction of the butterfly plate is relatively eccentric with the rotating center of the valve stem, makes the butterfly plate sealing surface gradually separate from the valve seat sealing surface during the opening process of the butterfly valve. When the butterfly plate rotates to 20° or up to 25°, the sealing surface of the butterfly plate is completely separated from the sealing surface of the valve seat, which greatly reduces the relative mechanical wear and extrusion between the two sealing surfaces during the opening process of the butterfly valve, thus improving the sealing performance of the butterfly valve. This design mainly relies on the elastic deformation between the butterfly plate and the valve seat to ensure the sealing of the butterfly valve.
Based on single eccentric butterfly valves, the rotating center of the butterfly plate is offset from the centerline of the valve flow passage, which makes the butterfly valve form a cam effect in the opening process, so that the sealing surface of the butterfly plate is separated from the sealing surface of valve seat faster than that of single eccentric structure. When the butterfly plate rotates to an angle from 8° to 12°, the sealing surface of the butterfly plate is completely separated from the sealing surface of the valve seat. The design of this structure greatly reduces the relative mechanical wear and extrusion deformation between the two sealing surfaces and improves the sealing performance of the butterfly valve.
On the basis of double eccentric butterfly valves, the centerline of the valve seat sealing surface and the centerline of the valve form an angular eccentricity, which makes the sealing surface of the butterfly plate separate from the valve seat sealing surface immediately at the opening moment, and then contact and press the valve seat sealing surface at the closing moment. This unique eccentric combination makes full use of the cam effect, completely eliminates the mechanical friction and scratch between the two sealing surfaces of the butterfly valve seal pair when the valve is opened and closed and eliminates the possibility of wear and leakage. The extrusion seal is changed into a torque seal, and the sealing specific pressure is adjusted by adjusting the external driving torque so that the sealing performance and service life of the butterfly valve with a triple eccentric structure are greatly improved.