The development of butterfly valve from its internal structure

1. Concentric butterfly valve

Concentric butterfly valve stem axis, disc center, valve center in the same position. Its structure is simple and easy to manufacture. Now the common rubber lined butterfly valve belongs to this kind of structure. Its disadvantages are that the butterfly plate and the valve seat are always in the state of extrusion and scraping, large resistance distance and fast wear. Because of these shortcomings, the butterfly valve of this kind of structure basically adopts flexible rubber or fluoroplastic and other soft sealing forms. But it's also limited by temperature.

2. Single eccentric butterfly valve

In order to solve the extrusion problem between the butterfly plate and the valve seat of concentric butterfly valve, the single eccentric butterfly valve is produced. The structure that the shaft axis of the valve rod deviates from the center of the butterfly plate is adopted, so that the upper and lower ends of the butterfly plate no longer become the rotary axis, disperse and reduce the excessive extrusion between the upper and lower ends of the butterfly plate and the valve seat. However, due to the single eccentric structure in the whole process of valve opening and closing, the scraping phenomenon between butterfly plate and valve seat has not disappeared, and the application range is similar to that of concentric butterfly valve, so it is not used much.

3. Double eccentric butterfly valve

Double eccentric butterfly valve is further improved on the basis of single eccentric butterfly valve, which is the most widely used double eccentric butterfly valve at present. The structure feature is that the shaft center of the valve rod deviates from the center of the butterfly plate and the center of the body. The effect of double eccentricity makes the butterfly plate break away from the valve seat immediately after the valve is opened, which greatly eliminates the unnecessary excessive extrusion and scratch between the butterfly plate and the valve seat, reduces the opening resistance, reduces the wear and improves the service life of the valve seat. The large reduction of scraping, at the same time, the double eccentric butterfly valve can also use metal seat, which improves the application of butterfly valve in the field of high temperature. However, because the sealing principle belongs to position sealing structure, that is, the sealing surface of butterfly plate and valve seat is in line contact, and the elastic deformation caused by squeezing the valve seat through butterfly plate produces sealing effect. Therefore, the requirements for closing position are very high (especially for metal valve seat), and the pressure bearing capacity is low. This is why people traditionally think that butterfly valve is not resistant to high pressure and has large leakage.

4. Triple eccentric butterfly valve

To withstand high temperature, hard seal must be used, but the leakage is large; to zero leakage, soft seal must be used, but not resistant to high temperature. In order to overcome the contradiction of double eccentric butterfly valve, the third eccentricity of butterfly valve was carried out. The structural features of the structure are that the conical axis of the butterfly plate sealing surface is inclined to the cylinder axis of the body while the shaft center of the double eccentric valve rod is eccentric. That is to say, after the third eccentricity, the sealing section of the butterfly plate is no longer true circle, but ellipse, and the shape of its sealing surface is asymmetric, one side is inclined to the body center line, and the other side is parallel to the body center line.

The biggest feature of the third eccentricity is that it fundamentally changes the sealing structure, which is no longer a position seal, but a torque seal. That is, 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. Therefore, the problem of zero leakage of metal valve seat is solved at one stroke, and the contact surface pressure is proportional to the medium pressure, and it is resistant to high pressure and high temperature readily solved.

Classification of butterfly valves
Classification by structure
(1) Center seal butterfly valve
(2) Eccentric single seal butterfly valve
(3) Double eccentric seal butterfly valve
(4) Eccentric triple seal butterfly valve

2. Classification by sealing surface material
(1) Soft seal butterfly valve
1) The sealing pair is composed of nonmetal soft material and nonmetal soft material.
2) The sealing pair is composed of hard metal material and non-metallic soft material.

(2)Metal hard seal butterfly valve. The sealing pair is composed of hard metal material and hard metal material.

3. Classification by sealing form

(1) Forced seal butterfly valve.

1) Elastic seal butterfly valve. The specific sealing pressure is generated by the elasticity of the valve plate squeezing the seat, seat or plate when the valve is closed.

2) Applied torque sealed butterfly valve. The seal specific pressure is generated by the torque applied to the valve shaft.

(2) Pressure sealed butterfly valve. The specific sealing pressure is generated by the charging of elastic sealing elements on the valve seat or valve plate.

(3) Automatic sealing butterfly valve. The sealing specific pressure is automatically generated by the medium pressure.

4. Classification by work pressure

(1) Vacuum butterfly valve. Butterfly valve with working pressure lower than standard atmospheric pressure.

(2) Low pressure butterfly valve. Butterfly valve with nominal pressure PN ≤ 1.6Mpa.

(3) Medium pressure butterfly valve. Butterfly valve with nominal pressure PN of 2.5-6.4mpa.

(4) High pressure butterfly valve. The butterfly valve with nominal pressure PN of 10.0-80.ompa.

(5) Ultra high pressure butterfly valve. Butterfly valves with nominal pressure PN > 100MPa.

5. Classification by operating temperature

(1) High temperature butterfly valve. t> 450 ℃ butterfly valve.

(2) Medium temperature butterfly valve. Butterfly valve with 120 ℃ < T ≤ 450 ℃.

(3) Normal temperature butterfly valve. -Butterfly valve with 40 ℃ < T ≤ 120 ℃.

(4) Low temperature butterfly valve. -Butterfly valve with 100 ℃ < T ≤ - 40 ℃.

(5) Ultra low temperature butterfly valve. T ≤ - 100 ℃.

6. Classification by connection mode

(1) Wafer butterfly valve

(2) Flange butterfly valve

(3) Trunnion butterfly valve

(4) Welded butterfly valve