The two eccentricities of the double offset butterfly valve refer to the eccentricity of the rotating center line of the disc and the eccentricity of the sealing line and the eccentricity of the center line of rotation of the disc and the center line of the channel.
What is principle of double offset butterfly valve?
The sealing principle of the double offset butterfly valve is that the butterfly valve can be sealed when the actual sealing specific pressure generated between the butterfly plate and the valve seat is greater than the required sealing specific pressure. The seal specific pressure is determined by the amount of elastic deformation generated by the valve seat. The cross-sectional shape of the butterfly seal's metal seal seat and disc seal is circular. Because the area of the medium acting on the valve seat is only the arc segment of the valve seat, the force arm is short and the amount of elastic deformation is small. The valve seat and the butterfly plate can only form a reliable seal when the medium pressure difference is low. For the pressure test of the butterfly valve of DN250, when the medium flow direction is positive and the medium pressure difference is greater than 0.3MPa, the valve will produce obvious visible leakage. When the flow direction of the medium is reversed and the pressure difference of the medium is greater than 0.8 MPa, the butterfly valve cannot be sealed again after one switch, and the valve seat has plastic deformation.
What leads to butterfly valve seal leakage?
The problem of seal leakage under the high-pressure difference of the butterfly valve is analyzed. Since the butterfly plate is mounted on the valve stem (the valve stem is equivalent to the simple support beam), when the medium pressure is positively applied to the butterfly plate, the force received by the butterfly plate is transmitted to the valve stem, and the valve stem will be Produces elastic deformation. At the same time, the butterfly plate also elastically deforms due to the action of the medium pressure, and the elastic deformation of the valve seat is smaller than the elastic deformation generated by the butterfly plate and the valve stem, resulting in a decrease in the sealing specific pressure formed between the butterfly plate and the valve seat. . When the actual seal specific pressure is less than the required seal specific pressure, the butterfly valve cannot achieve sealing. When the medium pressure acts on the butterfly plate in reverse, the amount of elastic deformation generated by the disc and the valve stem is greater than the limit of the elastic deformation of the valve seat. At this point, the actual seal specific pressure is greater than the allowable seal specific pressure, resulting in plastic deformation of the valve seat.
from: VALTECC China Butterfly Valve Suppliers and Manufacturers
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