Structural characteristics of triple eccentric butterfly valve

The eccentric butterfly valve has further improved in structural design compared to the center line butterfly valve, with its stem axis deviating from both the center of the butterfly plate and the center of the body. According to the degree of eccentricity and structural characteristics, eccentric butterfly valves can be further divided into single eccentric butterfly valves, double eccentric butterfly valves, and triple eccentric butterfly valves.

Single eccentric butterfly valve: The center of rotation of the butterfly plate (i.e. the center of the valve shaft) of the single eccentric butterfly valve is located on the centerline of the valve body and forms a certain size offset with the sealing section of the valve plate. When the valve is closed, the sealing surfaces of the valve seat and valve plate are in a relative interference contact state, mainly relying on the compression of the sealing ring to expand in the peripheral direction and generate sealing pressure, as well as the force of pipeline pressure on the valve plate to achieve sealing. This sealing method determines that single eccentric butterfly valves can generally only achieve one-way sealing. When the valve is opened, the contact between the valve plate and the valve seat is separated from the valve seat on one side, and the other side always contacts at two points along the axial direction of the semicircle. Frequent opening and closing operations can easily damage the sealing ring, thereby affecting the sealing performance, and it is difficult to achieve metal sealing. Single eccentric butterfly valves have certain applications in situations where sealing requirements are not particularly high, medium pressure is low, and flow direction is fixed.

Double eccentric butterfly valve: The double eccentric butterfly valve is developed on the basis of the single eccentric butterfly valve, and its structural feature is that the axis of the valve stem deviates from both the center of the butterfly plate and the center of the body. This dual eccentric design brings significant advantages. When the butterfly valve is opened, the butterfly plate can quickly detach from the valve seat, greatly reducing unnecessary excessive compression and scratching between the butterfly plate and the valve seat, effectively reducing the opening resistance torque, reducing wear, and improving the service life of the valve seat. Double eccentric butterfly valves can also use metal valve seats, which makes their application in high-temperature fields possible. However, the sealing principle of the double eccentric butterfly valve belongs to the position sealing structure, that is, the sealing surface between the butterfly plate and the valve seat is in line contact, and the sealing effect is produced by the elastic deformation caused by the compression of the valve seat by the butterfly plate. Therefore, the accuracy requirements for the closing position are high (especially in the case of metal valve seats), and there are disadvantages such as low pressure bearing capacity and large leakage. However, the double eccentric butterfly valve has been widely used in the industrial field due to its advantages in reducing wear and adapting to high temperatures, especially in situations where valve life and temperature adaptability are highly required.

Triple eccentric butterfly valve: The design of triple eccentric butterfly valve aims to overcome the contradiction between high temperature resistance and zero leakage of double eccentric butterfly valve. The so-called third eccentricity refers to the shape of the sealing pair not being a regular cone, but an oblique cone. This design enables the valve to achieve sealing effect by relying on the contact surface pressure of the valve seat when closed, solving the problem of zero leakage of metal valve seats in one fell swoop. Moreover, as the contact surface pressure is proportional to the medium pressure, the three eccentric butterfly valve can withstand high pressure and temperature, making it suitable for harsh working environments such as high temperature and high pressure, such as high-temperature and high-pressure pipeline systems in industries such as petrochemicals and power.