From the inside structure to see butterfly valve development process
Concentric Butterfly
Concentric butterfly valve stem axis, butterfly plate center, body center are in the same position. Its structure is simple, manufacturing is convenient, now the common rubber lined butterfly valve belongs to this structure. Its disadvantage is that due to butterfly plate and the valve seat is always in compression, scratch status, resistance distance is long, wear quickly. Alos because of these shortcomings, such structures butterfly valves are basicly adopted by the flexible rubber or soft fluoroplastic and other soft sealing forms. But it is also subject to temperature restrictions.
Single-eccentric butterfly valve
To address concentric butterfly valve disc and seat extrusion problem, resulting in a single eccentric butterfly valve, using stem axis deviated from the disc center structure, so makes the up and low ends of disc no longer to be a rotary axis, decentralized, thereby reducing the butterfly plate up and low ends and the seat excessive extrusion. However, as the single eccentric structure in the whole switching process, the disc and valve seat scratching phenomenon and not disappeared, is similar in the range of applications and concentric butterfly valve, so use not a lot.
Double eccentric butterfly valve
Double eccentric butterfly valve is further improved and shaped based on single eccentric butterfly valve, is now the most widely used double eccentric butterfly valve. Their structural characteristic is in the stem axis both deviated from the disc center and the body center. The effect of double eccentric makes the disc immediately separate from the valve seat after valve is opened and substantially eliminating unnecessary disc and the valve seat over-compression, scratch phenomenon, thereby reducing the opening resistance, reducing wear and tear, increase seat life. Significant reduction of scratch, while also making double eccentric butterfly valve can use metal seat, to improve the butterfly valve using in high-temperature fields. However, because its sealing principle belongs to position sealing structure, that is, the butterfly plate and the valve seat sealing surface is the line contaction, through the disc presses valve seat caused elastic deformation to form sealing effect, it is high requirement on the closed position (especially metal seat), low-pressure capability, that is why traditionally people think the butterfly valve is not high-pressure resistance, large leakages.
Three eccentric butterfly valve
To high temperature resistance, you must use hard sealing, but with large amount of leakage; to achieve zero leakage, you must use soft sealing, but not high temperature resistance. To overcome double eccentric butterfly valve this contradiction, make the third time eccentric on the butterfly valve. The structural characteristics are at the same time the double eccentric stem axis position bias, makes the butterfly plate sealing surface of the cone axis deflection in the cylindrical body axis, ie, after the third eccentric, the disc sealing section is no longer true circle, but the oval shape, its sealing surface is also because of this,so asymmetry, one side is tilt in body centerline, the other side is parallel to the body centerline.
This third eccentric most important feature is to change the sealing structure fundamentally, is no longer location-sealed, but the torque-sealed, that is, not relying on the elastic deformation of the valve seat, but rely entirely on the valve seat contact surface pressure to achieve the sealing effect. Therefore, solve this problem that the metal valve seat zero leakage in one fell swoop, and because of contacting surface pressure and medium pressure is proportionate, high pressure resistance and high temperature resistance are also resolved.
