The structural feature of this kind of China butterfly valve is that the shaft center of the valve stem, the center of the disc and the center of the body are in the same position. The structure is simple and the manufacture is convenient.
Common rubber-lined butterfly valves belong to this category. The disadvantage is that the butterfly plate and the valve seat are always squeezed and scraped, the resistance is large, and the wear is fast. In order to overcome extrusion, scratches and ensure sealing performance, the valve seat is basically made of elastic materials such as rubber or PTFE, but it is also limited by temperature in use. This is why traditionally people think that butterfly valves are not resistant to high temperature. reason.
In order to solve the extrusion problem between the disc and the valve seat of the concentric butterfly valve, the single eccentric butterfly valve is produced. Heart, dispersion, and reduce the excessive extrusion of the upper and lower ends of the butterfly plate and the valve seat.
However, due to the single eccentric structure, the scraping phenomenon between the disc and the valve seat does not disappear during the entire opening and closing process of the valve, and the application range is similar to that of the concentric butterfly valve, so it is not used much.
Structural features of single eccentric butterfly valve:
(1) The center of rotation of the disc plate (ie, the center of the valve shaft) is located on the centerline of the valve body, and forms a dimensional offset with the sealing section of the valve plate. The single eccentric butterfly valve is that the rotation center of the disc plate is on the center line of the valve body, and the valve plate deviates a distance from the sealing surface, which is suitable for soft sealing.
(2) When the valve is closed, the valve seat and the valve plate sealing surface are in a state of relative interference. To achieve sealing, the sealing is mainly achieved by pressing the sealing ring to expand it in the peripheral direction to generate sealing specific pressure and pipeline pressure to the valve. The force of the plate makes it reach the seal, so it can only be sealed in one direction.
(3) When the valve is opened, the contact side of the valve plate and the valve seat is separated from the valve seat, and the other side is always in two-point contact along the axial direction of the semi-circle. Repeated opening and closing of the sealing ring is easy to damage, which affects the sealing performance. Even more impossible to achieve a metal seal.
The double eccentric butterfly valve is further improved on the basis of the single eccentric butterfly valve, which is the most widely used double eccentric butterfly valve.
Structural features of double eccentric butterfly valve:
The center of rotation of the valve plate (that is, the center of the valve shaft) forms a dimensional offset in the sealing section of the valve plate, and forms a dimensional offset in the center of the valve body.
Its structural feature is that the shaft center of the valve stem deviates from the center of the disc and the center of the body. The effect of double eccentricity enables the disc to break away from the valve seat immediately after the valve is opened, which greatly eliminates unnecessary excessive extrusion and scratching between the disc and the valve seat, reduces the opening resistance, reduces wear, and improves the Seat life. The large reduction of scraping also enables double eccentric China butterfly valves to use metal valve seats, which improves the application of butterfly valves in high temperature fields.
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