What is a trieccentric butterfly valve?

What is a trieccentric butterfly valve?

The valve stem axis deviates from the center of the disc and the center of the body at the same time, and the rotation axis of the valve seat has a certain angle with the axis of the valve body channel, which is called a trieccentric butterfly valve.

20201215075313 58219 - What is a trieccentric butterfly valve?

Features of triple eccentric butterfly valve

The triple eccentric butterfly valve is widely used in metallurgy, electric power, petrochemical, water supply and drainage, and municipal construction and other industrial pipelines with a medium temperature of 425 ℃ or less to adjust the flow rate and carry out the fluid. The material is divided into: cast iron, cast steel, stainless steel, its main features are:

API specifications

As we all know, API609 has actually become the international standard for valves used in important industrial pipelines. Yaang is designed and manufactured in strict accordance with the latest 1997 version of API609 specifications. What’s more valuable is that the basic design of Yaang is not limited to only one API specification, BS5155 ANSI B 16.34, ASME SEC VIII and other major specifications can be corresponded to, which ensures that Yaang is useful in all industrial fields.

Double safety structure

  • Yaang strictly complies with API609 specifications, in order to prevent the deformation of the butterfly plate caused by the influence of fluid pressure and temperature, the dislocation of the valve stem, the sealing surface occlusion, and two independent thrust rings are installed on the upper and lower sides of the butterfly plate. So as to ensure the normal operation of the valve under any working conditions.
  • At the same time, in order to prevent unexpected accidents caused by valve stem damage and flying out caused by unknown reasons, independent valve stem flying out prevention mechanisms are designed at the lower end of the valve, which also guarantees the pressure level of Yaang from the side. It can be as high as 2500 pounds.

No dead zone design

In the design process, Yaang specially considered the application problem in the field of control, and made full use of the sealing principle of the triple-eccentric butterfly valve to ensure that the butterfly plate does not scratch the valve seat when the valve is opened and closed, and the torque of the valve stem is directly transmitted to the seal through the butterfly plate. This means that there is almost no friction between the butterfly plate and the valve seat, which eliminates the common jumping phenomenon when opening ordinary valves, and eliminates the control caused by various unstable factors such as friction in the low opening range of the valve. Inability to phenomenon, that is to eliminate the dead zone (no sensing zone), which means that Yaang can almost enter the adjustable area from 0 opening to 90 opening, its normal control ratio is more than twice that of ordinary butterfly valves, and the control ratio is the highest It can be as high as 100:1 or more. This creates good conditions for Yaang to be used as a control valve, especially when the diameter is large, the cost of the shut-off valve is extremely high, in addition, the shut-off valve cannot achieve zero leakage, and the shut-off valve must be used in conditions that require emergency shutdown. A shut-off valve is installed on the side of the Yaang, and Yaang integrates control and shut-off, and its economic benefits are extremely considerable.

Body valve seat structure

There are two valve seat installation structures for triple eccentric butterfly valves. Most of them are installed on the butterfly plate for the convenience of the diagram, but Yaang uses a body seat structure to install the valve seat on the body. Its advantage is that compared with the butterfly valve seat, it greatly reduces the chance of the valve seat directly contacting the medium, thereby reducing the degree of erosion of the valve seat and prolonging the service life of the valve seat.

Thin layer valve seat structure

Yaang’s valve seat is made of laminated stainless steel sheets and graphite sheets. This structure can effectively prevent the influence of small solids in the medium and the sealing surface seizure that may be caused by thermal expansion. Even if there is a small damage, there will be no leakage. , And this is unimaginable for double eccentric butterfly valves or other triple eccentric butterfly valves.

Replaceable seal pair

Yaang’s sealing pair is unique. Not only the body valve seat can be replaced, but also because the butterfly plate sealing surface and the butterfly plate are independent, the butterfly plate sealing surface can also be replaced, which means that when the butterfly plate sealing surface is damaged, there is no need to Xingshi mobilizes to transport it back to the manufacturing plant or disassemble the valve on a large scale, and only need to change the sealing surface of the butterfly plate. This not only greatly reduces the maintenance cost, but also greatly reduces the maintenance man-hours and the intensity and difficulty of the maintenance.

Balanced fixed structure

Starting from the shape characteristics of the sealing surface of the triple eccentric butterfly valve, Yaang’s sealing pair is fixed by bolts in an elliptical distribution, which not only has accurate positioning, but also makes each bolt receive a balanced force, eliminating the uneven distribution of stress. The sealing pair is loose and leaking.

The structure of triple eccentric butterfly valve

Essential refractory structure

Many valves claim to have a fire-resistant structure, but most of them use a soft and hard double seat structure to reduce leakage. In fact, this is very dangerous. Because the incomplete combustion of the soft-seal valve seat during a fire will cause the metal supporting valve seat to produce stress and temperature difference deformation, which will lead to the failure of the refractory function. Therefore, currently Europe and the United States are gradually eliminating this type of refractory valve that does not deserve its name. Yaang is a zero-leakage, so it does not require the help of a soft seal. It is a veritable essential fire-resistant structure and has obtained API607, API6FA and BS6755Part2 fire-resistant inspection certificates. This ensures that Yaang can be used in various hazardous areas such as petroleum and petrochemicals. Yaang covers almost all the valves used in various key parts of the conservative Britain and North Sea oil fields.

High sealing packing structure

In terms of valve leakage, traditionally, the leakage of the valve seat, that is, internal leakage, is often concentrated, while the leakage of the packing part, that is, external leakage is ignored. In fact, in contemporary society where environmental issues are being increasingly valued, it is an indisputable fact that leakage is far more harmful than internal leakage. The Yaang triple eccentric butterfly valve is a rotary valve, and its stem movement is only 90 ° rotation. This is compared with the valve stem movement of gate valves, globe valves, etc., which is spiral multi-turn reciprocating motion. The service life of the ground is very long, and because Yaang adopts the highest standard design in the external leakage prevention structure of the packing seal, so that the standard sealing performance can be guaranteed to be below 100ppm when the external leakage test is performed in accordance with EPA21 specifications.

Development and application of triple eccentric butterfly valve

The early butterfly valve was not able to withstand high temperature and pressure and had a large amount of leakage, which greatly restricted its application range. In order to meet the requirements of various working conditions, the butterfly valve has experienced the evolution from concentric to single eccentric, double eccentric and triple eccentric.
The structural feature of the concentric 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 manufacturing is convenient. The disadvantage is that the butterfly plate and the valve seat are always in the state of squeezing and scratching, the resistance distance is large, and the wear is fast. In order to solve the problem of the extrusion of the butterfly plate and the valve seat of the concentric butterfly valve, a 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 lower end of the butterfly plate no longer becomes the rotation axis. Disperse and reduce the excessive squeezing between the lower end of the butterfly plate and the valve seat. However, because the single eccentric structure only reduces to a certain extent during the entire switching process of the valve, it does not eliminate the scratching phenomenon between the butterfly plate and the valve seat, and the application range is similar to the concentric butterfly valve, so it is not used much.
On the basis of the single eccentric butterfly valve, the further improved shape is the double eccentric butterfly valve which is widely used at present. Its structural feature is that the axis of the valve stem deviates from the center of the butterfly plate and the center of the valve body.
The double eccentric effect enables the butterfly plate to be released from the valve seat immediately after the valve is opened, which greatly eliminates unnecessary excessive squeezing and scraping of the butterfly plate and the valve seat, reduces the opening resistance, reduces wear and extends seat life. The scraping is greatly reduced, and at the same time, the double eccentric butterfly valve can also use a metal seat, which improves the application of the butterfly valve in the high temperature field. But because its sealing principle is a positional sealing structure, that is, the sealing surface of the butterfly plate and the valve seat is in line contact, and the elastic deformation caused by the butterfly plate squeezing the valve seat produces a sealing effect, so the closing position is very demanding (especially metal Valve seat), low pressure bearing capacity, which is why traditionally people think that butterfly valves are not resistant to high pressure and have large leakage.
To withstand high temperatures, hard seals must be used, but the amount of leakage is large; for zero leakage, soft seals must be used, but they are not resistant to high temperatures. In order to overcome the contradiction of the double eccentric butterfly valve, the butterfly valve was eccentric for the third time.
In many Asia-Pacific countries, due to the limitation of their own valve design and manufacturing level and the influence of traditional textbooks, the prejudice against butterfly valves is still very large. At the same time, advanced and developed industrial countries in Europe and America are vigorously promoting and actively using butterfly valves. The reason is very simple, the butterfly valve is no longer what it used to be.
The scope of application of triple eccentric butterfly valve can withstand pressure up to 2500 pounds, temperature resistance as low as -196 ℃, up to 700 ℃, sealing to 0 leakage, and control ratio as high as 100:1. That is to say, in all kinds of harsh and critical process control pipelines, whether it is an on-off valve or a control valve, as long as the type is properly selected, the butterfly valve can now be safely used at low cost.
The excellent performance of the butterfly valve is closely related to its continuous eccentricity, evolution and development. In order to meet the requirements of various working conditions, the butterfly valve has experienced the evolution from concentric to single eccentric, double eccentric and triple eccentric. The evolution of the butterfly valve and the development and application of the triple eccentric butterfly valve are briefly introduced as follows:

Classification of butterfly valve

  • 1. Concentric butterfly valve The structural feature of this 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 manufacturing is convenient. Common rubber-lined butterfly valves belong to this category. The disadvantage is that the butterfly plate and the valve seat are always in a state of squeezing and scratching, large resistance distance, and fast wear. In order to overcome squeezing, scratching, and to ensure sealing performance, the valve seat is basically made of rubber or PTFE and other elastic materials, but it is also subject to temperature restrictions in use. This is why traditionally people think that butterfly valves are not resistant to high temperatures. the reason.
  • 2. The single eccentric butterfly valve is to solve the problem of extrusion between the butterfly plate and the valve seat of the concentric butterfly valve, resulting in a single eccentric butterfly valve. Its structural feature is that the stem axis deviates from the center of the butterfly plate, so that the upper and lower ends of the butterfly plate are no longer It becomes the axis of rotation, disperses, and reduces the excessive extrusion between the upper and lower ends of the butterfly plate and the valve seat. However, because the single eccentric structure does not disappear from the scratching phenomenon of the butterfly plate and the valve seat during the entire switching process of the valve, and the application range is similar to that of the concentric butterfly valve, it is not used much.
  • 3. Double eccentric butterfly valve. On the basis of the single eccentric butterfly valve, the most widely used double eccentric butterfly valve is further improved. Its structural feature is that the axis of the valve stem deviates from the center of the butterfly plate and the center of the body. The double eccentric effect enables the butterfly plate to be released from the valve seat immediately after the valve is opened, which greatly eliminates unnecessary excessive extrusion and scratching of the butterfly plate and the valve seat, reduces the opening resistance, reduces wear and improves The life of the valve seat is improved. The scraping is greatly reduced, and the double eccentric butterfly valve can also use metal seat, which improves the application of the butterfly valve in the high temperature field. But because its sealing principle is a positional sealing structure, that is, the sealing surface of the butterfly plate and the valve seat is in line contact, the elastic deformation caused by the butterfly plate squeezing the valve seat produces a sealing effect, so the closing position is very demanding (especially metal Valve seat), low pressure bearing capacity, this is why traditionally people think that butterfly valves are not resistant to high pressure and have large leakage.
  • 4. The triple eccentric butterfly valve must be resistant to high temperature and must use a hard seal, but the leakage is large; if there is no leakage, a soft seal must be used, but it is not resistant to high temperature. In order to overcome the contradiction of the double eccentric butterfly valve, the butterfly valve was eccentric for the third time. Its structural feature is that while the double eccentric valve stem axis position is eccentric, the conical axis of the butterfly plate sealing surface is skewed to the cylinder axis of the body, that is, after the third eccentricity, the sealing section of the butterfly plate is not Furthermore, it is a true circle, but an ellipse, and its sealing surface shape is therefore asymmetrical, one side is inclined to the center line of the body, and the other side is parallel to the center line of the body. The biggest feature of this third eccentricity is that it fundamentally changes the sealing structure. It is no longer a positional seal, but a torsion 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 sealing. Therefore, the problem of zero leakage of the metal valve seat is solved in one fell swoop, and because the contact surface pressure is proportional to the medium pressure, the high pressure and high temperature resistance is also solved.

Development of triple eccentric butterfly valve

Since its inception, the triple eccentric butterfly valve has undergone a process of self-improvement and continuous development in order to meet increasingly severe working conditions. Even if the most basic zero leakage and triple eccentric butterfly valve can be achieved in theory, it still depends on careful design and precise manufacturing.

The application of triple eccentric butterfly valve

In summary, the triple eccentric butterfly valve, as the crystallization of the latest valve technology, will take advantage of the advantages of various valves and avoid the shortcomings of various valves, and it will certainly receive more and more attention from users and designers. The maximum pressure level can reach 2500 pounds, the standard caliber can reach 48 inches, and the clamp, lug, flange, ring connection, butt welding, jacket, various structural lengths, etc. can be corresponded, and more due to material selection There is a lot of room, high and low temperature, and various acids, alkalis and other corrosive media can be handled freely. Especially in terms of large diameter, with its zero leakage advantage, in the shut-off valve, it is constantly replacing the large gate valve and ball valve. Similarly, with its excellent control function, it is also constantly replacing the bulky control valve. Shut-off valve. As a fact, it is used in various important pipelines including China’s oil and gas exploration, offshore platforms, petroleum refining, petrochemicals, inorganic chemicals, energy power generation and other major industrial fields such as process control.

The difference between centerline butterfly valve, single eccentric, double eccentric and triple eccentric butterfly valve

Centerline butterfly valve (concentric butterfly valve)

The structural feature of the centerline butterfly valve (concentric 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 manufacturing is convenient. Common rubber-lined butterfly valves belong to this category. The disadvantage is that the butterfly plate and the valve seat are always in a state of squeezing and scratching, large resistance distance, and fast wear. In order to overcome squeeze, scratches, and ensure sealing performance, the valve seat basically uses elastic materials such as rubber or polytetrafluoroethylene, but it is also limited by the temperature in the use of the sealing material. This is why traditionally people think that butterfly valves are not resistant. The cause of high temperature.

Single eccentric butterfly valve

The structural feature of the single eccentric butterfly valve is that the shaft center of the valve stem deviates from the center of the butterfly plate, so that the lower end of the butterfly plate no longer becomes the rotation axis, disperses, reduces the excessive extrusion between the upper end of the butterfly plate and the valve seat, and solves the concentric butterfly valve. The squeeze problem of the butterfly plate and the valve seat. However, because the single eccentric structure does not disappear from the scratching phenomenon of the butterfly plate and the valve seat during the entire switching process of the valve, and the application range is similar to that of the concentric butterfly valve, it is not used much.

Double eccentric butterfly valve

The double eccentric butterfly valve is further improved on the basis of the single eccentric butterfly valve, and the application is also the most extensive. Its structural feature is that the axis of the valve stem deviates from the center of the butterfly plate and the center of the body. The double eccentric effect enables the butterfly plate to be released from the valve seat immediately after the valve is opened, which greatly eliminates unnecessary excessive extrusion and scratching of the butterfly plate and the valve seat, reduces the opening resistance, reduces wear and improves The life of the valve seat is improved. The scraping is greatly reduced, and the double eccentric butterfly valve can also use metal seat, which improves the application of the butterfly valve in the high temperature field. But because its sealing principle is a positional sealing structure, that is, the sealing surface of the butterfly plate and the valve seat is in line contact, the elastic deformation caused by the butterfly plate squeezing the valve seat produces a sealing effect, so the closing position is very demanding (especially metal Valve seat), low pressure bearing capacity, this is why traditionally people think that butterfly valves are not resistant to high pressure and have large leakage.

Triple eccentric butterfly valve

To withstand high temperatures, hard seals must be used, but the amount of leakage is large; for zero leakage, soft seals must be used, but they are not resistant to high temperatures. In order to overcome the contradiction of the double eccentric butterfly valve, the butterfly valve was eccentric for the third time. Its structural feature is that while the double eccentric valve stem axis position is eccentric, the conical axis of the butterfly plate sealing surface is skewed to the cylinder axis of the body, that is, after the third eccentricity, the sealing section of the butterfly plate is not Furthermore, it is a true circle, but an ellipse, and its sealing surface shape is therefore asymmetrical, one side is inclined to the center line of the body, and the other side is parallel to the center line of the body.
The characteristic of this third eccentricity is that the sealing structure is fundamentally changed. It is no longer a positional seal, but a torsion seal, that is, it does not rely on the elastic deformation of the valve seat, but completely depends on the contact surface pressure of the valve seat to achieve the sealing effect. , Therefore, the problem of zero leakage of the metal valve seat is solved in one fell swoop, and because the contact surface pressure is proportional to the medium pressure, the high pressure and high temperature resistance is also solved.

Source: China Valve Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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Summary
what is a trieccentric butterfly valve - What is a trieccentric butterfly valve?
Article Name
What is a trieccentric butterfly valve?
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The valve stem axis deviates from the center of the disc and the center of the body at the same time, and the rotation axis of the valve seat has a certain angle with the axis of the valve body channel, which is called a trieccentric butterfly valve.
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www.steeljrv.com
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