Butterfly valve, also known as flap valve, is often used in pipelines for conveying various corrosive and non-corrosive fluid media in engineering systems such as generators, coal gas, natural gas, liquefied petroleum gas, hot and cold air, chemical smelting, etc., for regulating and cutting off flow of the medium.
A butterfly valve is a valve that uses a circular butterfly plate as an opening and closing member and rotates with the valve stem to open, close and adjust the fluid channel. The butterfly plate of the butterfly valve is installed in the diameter direction of the pipeline. In the cylindrical channel of the butterfly valve body, the disc-shaped butterfly plate rotates around the axis, and the rotation angle is between 0° and 90°. When it rotates to 90°, the valve is in a fully open state. By changing the deflection angle of the disc, the flow of the medium can be controlled.
(1) Concentric butterfly valve
The structural feature of this kind of butterfly valve is that the shaft center of the valve stem, the center of the butterfly plate 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 due to the fact that the butterfly plate and the valve seat are always in a state of extrusion and scraping, the resistance distance is large and the wear is fast.
(2) Single eccentric butterfly valve
In order to solve the extrusion problem of the disc and the valve seat of the concentric butterfly valve, the single eccentric butterfly valve was produced. Its structural feature is that the shaft center of the valve stem deviates from the center of the butterfly plate, so that the upper and lower ends of the butterfly plate no longer become the rotation axis, which disperses and reduces the excessive extrusion between the upper and lower ends of the butterfly plate and the valve seat.
(3) Double offset butterfly valve
On the basis of the single eccentric butterfly valve, the most widely used double offset butterfly valve is further improved and formed. 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 of the disc and the valve seat, reduces the opening resistance, reduces wear, and improves the performance of the valve. Seat life.
(4) Triple offset butterfly valve
To withstand high temperature, a hard seal must be used, but the amount of leakage is large; to zero leakage, a soft seal must be used, but it is not resistant to high temperature. In order to overcome the contradiction of the double offset butterfly valve, the butterfly valve has been eccentric for the third time (deviation from the center line of the metal sealing surface). The structure is characterized in that the conical axis of the sealing surface of the butterfly plate is deviated from the cylinder axis of the body while the position of the double eccentric valve stem is eccentric. That is to say, after the third eccentricity, the sealing section of the disc is no longer a true circle, but an ellipse. The biggest feature of the triple offset butterfly valve is that the sealing structure is fundamentally changed. It is no longer a position seal, but a torsion seal; it does not rely on the elastic deformation of the valve seat, but completely relies on the contact surface pressure of the valve seat to achieve the sealing effect.