Sealing Principle of Double Eccentric Sealed Butterfly Valve

(1) Structural characteristics. The rotary center of the valve plate (i.e. the center of the valve shaft) forms a dimension a offset with the sealing section of the valve plate, and a dimension B offset with the center line of the valve body.

(2) Sealing principle. Because the center of rotation of the valve plate (i.e. the center of the valve shaft) is offset by the center line of the valve body on the basis of the single eccentric sealed butterfly valve, when the double eccentric sealed butterfly valve is fully opened, the sealing surface of the valve plate will be completely separated from the sealing surface of the valve seat, and a ratio sheet will be formed between the sealing surface of the valve plate and the sealing surface of the valve seat. In eccentrically sealed butterfly valve, the clearance y with larger x clearance can be seen from figure (11). Because of the offset of size b, the rotating radius of the valve plate can be divided into long radius rotation and short radius rotation. On the large half circle of the valve plate rotating with long radius, the tangent of the rotating track of the valve plate sealing surface will form a zero angle with the seat sealing surface, which will make the valve open and close when the valve plate is opened or closed. The plate sealing surface acts as a gradual release and gradual extrusion relative to the seat sealing surface, thus reducing the mechanical wear and abrasion between the two sealing surfaces of the butterfly valve seal pair when the valve plate is opened and closed. When the valve plate of this kind of butterfly valve is opened from 0 to 90, the sealing surface of the valve plate will leave the seat sealing surface faster than that of the single eccentric sealing butterfly valve.  Usually, when the valve plate rotates from 0 to 8 to 12, the sealing surface of the valve plate can be completely separated from the sealing surface of the valve seat, so that the mechanical wear and extrusion angle travel between the valve plate and the sealing surface of the valve seat is shorter in the process of opening and closing, thus the mechanical wear and extrusion deformation are reduced, and the sealing performance of the butterfly valve is improved. When Closing Butterfly valve, through the rotation of the valve plate, the outer sealing surface of the valve plate gradually approaches and extrudes the PTFE and spring steel wire composite valve seat, which produces elastic deformation and forms elastic force as the sealing specific pressure to ensure the sealing of the butterfly valve. The function of PTFE winding with spring steel wire is to make the seat more elastic and better.

(3) The main reasons for the failure of sealing performance of sealing pairs.

1) In the opening and closing process of butterfly valve, when the valve plate rotates and extrudes the elastic soft seat, mechanical wear and abrasion occur between the valve plate and the seat.

2) Permanent plastic deformation, cold flow and elastic failure occur in the elastic seat or elastic layer of the valve plate after the valve plate extrudes the elastic seat.

3) Material aging failure of elastic seat or elastic layer of valve plate, etc.

4) Cavitation erosion of medium and erosion of sealing surface.

(4) The characteristics of double eccentric sealed butterfly valve.

1) The structure of butterfly valve with single eccentric seal is more complex and the cost is slightly higher than that of butterfly valve with single eccentric seal.

2) The sealing performance is better than that of single eccentric butterfly valve.

3) The service life of the butterfly valve is longer than that of the single eccentric sealing valve, and the service pressure is also higher.

Double eccentric butterfly valve  

1. Double eccentric full-lined rubber butterfly valve

(1) Overview of uses

The butterfly valve has the advantages of rubber lined butterfly valve and eccentric soft sealing butterfly valve. It is suitable for cutting off fluid in special pipelines with weak acid, alkali and other corrosive media in seawater and other media.

And adjust the medium flow rate and other functions.

(2) Characteristics and advantages

1) Double eccentric structure, small friction moment, quick opening and closing, flexible operation, light and labor-saving.

2) Valve body and butterfly plate are all rigid rubber vulcanized lining, so that the medium and metal valve body and butterfly plate are finished.

Totally isolated.

3) It combines all the advantages of common center plate butterfly valve with rubber lining and double eccentric soft sealing butterfly valve.

4) Zero leakage of bidirectional seal.

5) It is especially suitable for corrosive fluid media such as sea water, with long service life and good economy.

Geometric design

Eccentricity 1: Eccentricity H of axis of valve shaft to sealing center line

Eccentricity 2: Eccentricity E of Valve Shaft Axis to Pipeline Axis

Conical angle alpha: Conical angle alpha of seat sealing surface

Lining: 3mm thick vulcanized hard rubber lining for valve body and butterfly plate

Note: Other shapes and sizes are the same as common double eccentric soft seal butterfly valves.

2. Telescopic butterfly valve

(1) Overview of uses

The expansion butterfly valve has the function of automatically compensating the thermal expansion and cold contraction of pipeline for convenient loading and unloading. It is used for water supply and drainage of petroleum, chemical industry, electric power, paper making, food, medicine and municipal construction under 425C temperature and 2.5MPa nominal pressure, and for regulating flow rate and cutting off fluid medium in gas pipeline.

(2) Characteristics and advantages

1) Unique structure, flexible operation, light weight, easy operation and labor-saving, quick opening and closing.

2) The expansion butterfly valve can not only adjust and shut off the flow and compensate the thermal expansion and cold contraction caused by the temperature difference of the pipeline, but also provide convenience for the installation and replacement of the maintenance valve.

3) Sealing parts can be adjusted and replaced, and the sealing performance is reliable.

4) It has the function of butterfly valve and pipeline expansion, which can save cost.

5) Different materials can be selected according to the working conditions.