Double Eccentric Butterfly Valve Guide

Butterfly valves play a vital role in industrial process control. Among them, double eccentric butterfly valves are particularly popular in certain applications due to their unique design and performance characteristics. In this article, we will introduce double eccentric butterfly valve and its related knowledge points in detail.

1.What is a double eccentric butterfly valve?

The so-called double eccentricity, the first eccentricity refers to the stem shaft deviation from the centre of the sealing surface, that is, the stem shaft is behind the butterfly plate surface. This eccentricity makes the contact surface of the butterfly plate and valve seat are sealing surface, which fundamentally overcomes the inherent shortcomings of the centre line butterfly valve, thus eliminating the possibility of internal leakage at the upper and lower intersection between the stem shaft and the sealing valve seat.

Another eccentricity refers to the centre of the overwater hole of the valve body and the axis of the valve stem is shifted to the left and right, that is, the axis of the valve stem separates the butterfly plate into two parts of one side and the other side is less. This eccentricity can make the butterfly plate in the opening and closing process can be quickly detached from or close to the valve seat, reduce the friction between the butterfly plate and the sealing seat travel, reduce wear and tear, reduce the opening and closing torque, extend the service life of the valve seat.

Double eccentric butterfly valve's butterfly plate periphery and sealing seat are processed into hemispherical surface, relying on the outer sphere of the butterfly plate to squeeze the inner sphere of the sealing seat to produce elastic deformation to achieve the purpose of shutting down. The double eccentric butterfly valve usually adopts PTFE material as its sealing seat, and it can also adopt metal sealing seat to expand its application in high temperature field. However, the sealing of double eccentric butterfly valve with metal sealing seat still belongs to positional sealing structure, i.e. the sealing surface of butterfly plate and valve seat is in line contact, so it is not able to withstand high pressure, which will inevitably lead to a larger leakage when applied in high-pressure system. Therefore, in the high-pressure or the system requiring tight cut-off, the use of double eccentric butterfly valves with metal sealing seat should be avoided as much as possible.

2. double eccentric butterfly valve working principle

Double Eccentric Butterfly Valve is a kind of valve that uses disc type opening and closing parts to reciprocate about 90° to open, close or regulate the flow of medium. Butterfly valve is not only simple structure, small size, light weight, material consumption, small installation size, small driving torque, easy to operate, rapid, and can also have a good flow regulation and closing sealing characteristics, butterfly valve is widely used. The use of its varieties and the number continues to expand, and to high temperature, high pressure, large calibre, high sealing, long life, excellent regulating characteristics, as well as a multi-functional development of the valve. Its reliability and other performance indicators have reached a high level.

With the application of chemical corrosion-resistant synthetic rubber on the butterfly valve, the performance of the butterfly valve can be improved. As synthetic rubber has corrosion resistance, erosion resistance, dimensional stability, good resilience, easy to form, low cost and so on, and can be used according to different requirements for the selection of different properties of synthetic rubber to meet the use of butterfly valve working conditions.

As polytetrafluoroethylene (PTFE) has strong corrosion resistance, stable performance, not easy to aging, low coefficient of friction, easy to form, dimensional stability, and can be filled, add appropriate materials to improve its comprehensive performance, to get a better strength, lower coefficient of friction of the butterfly valve sealing material, to overcome the limitations of the synthetic rubber, and therefore the polymer polymer materials represented by polytetrafluoroethylene and its filler modified materials. As a result, polymer polymerisation materials represented by PTFE and its filler modification materials are widely used in butterfly valves, thus the performance of butterfly valves is further improved and butterfly valves with wider temperature and pressure range, reliable sealing performance and longer service life are manufactured.

In order to meet the use of high and low temperature, strong erosion, long life and other industrial applications, metal sealed butterfly valves have been greatly developed. With the application of high temperature resistance, low temperature resistance, strong corrosion resistance, strong erosion resistance, high strength alloy materials in butterfly valves, so that the metal-sealed butterfly valves in the high and low temperatures, strong erosion, long life and other industrial applications, the emergence of a large calibre (9~750mm), high pressure (42.0MPa), a wide range of temperatures (-196~606 ℃) butterfly valves, so that the butterfly valve technology to reach a A whole new level.

 The butterfly valve has a small flow resistance when fully opened. When opened between about 15°~70°, it can also carry out sensitive flow control, so in the field of large-diameter regulation, the butterfly valve is very commonly used.

As the movement of the butterfly plate is wiping, most butterfly valves can be used for media with suspended solids. Depending on the strength of the seals, they can also be used for powdery and granular media.

3. What are the advantages and disadvantages of double eccentric butterfly valves?

Advantages:

• Minimal friction: Due to its double eccentric design, friction between the valve flap and the valve seat is significantly reduced, thus extending the service life of the valve.

• Good sealing performance: The double eccentric design ensures that the valve flap has good contact with the valve seat in the closed position, resulting in an efficient seal.

• Compact structure: double eccentric butterfly valves are usually more compact and easier to install than traditional butterfly valves.

Disadvantages:

• High cost: compared with conventional butterfly valves, double eccentric butterfly valves are more expensive to manufacture.

• High maintenance requirements: due to their complex design, double eccentric butterfly valves may require specialised skills and experience when it comes to maintenance.

4. Where are double eccentric butterfly valves mainly used?

Double Eccentric Butterfly Valves are mainly used in applications where high sealing performance and long life are required, such as:

Double Eccentric Butterfly Valve is a kind of valve that uses disc type opening and closing parts to reciprocate about 90° to open, close or regulate the flow of medium. Butterfly valve is not only simple structure, small size, light weight, material consumption, small installation size, small driving torque, easy to operate, rapid, and can also have a good flow regulation and closing sealing characteristics, butterfly valve is widely used. The use of its varieties and the number continues to expand, and to high temperature, high pressure, large calibre, high sealing, long life, excellent regulating characteristics, as well as a multi-functional development of the valve. Its reliability and other performance indicators have reached a high level.　　

With the application of chemical corrosion-resistant synthetic rubber on the butterfly valve, the performance of the butterfly valve can be improved. As synthetic rubber has corrosion resistance, erosion resistance, dimensional stability, good resilience, easy to form, low cost and so on, and can be used according to different requirements for the selection of different properties of synthetic rubber to meet the use of butterfly valve working conditions.　　

As polytetrafluoroethylene (PTFE) has strong corrosion resistance, stable performance, not easy to aging, low coefficient of friction, easy to form, dimensional stability, and can be filled, add appropriate materials to improve its comprehensive performance, to get a better strength, lower coefficient of friction of the butterfly valve sealing material, to overcome the limitations of the synthetic rubber, and therefore the polymer polymer materials represented by polytetrafluoroethylene and its filler modified materials. As a result, polymer polymerisation materials represented by PTFE and its filler modification materials are widely used in butterfly valves, thus the performance of butterfly valves is further improved and butterfly valves with wider temperature and pressu

Double eccentric butterfly valve is suitable for flow regulation. Since the pressure loss of butterfly valve in the pipeline is relatively large, it should also consider the robustness of the butterfly plate to withstand the pressure of the pipeline medium when it is closed. In addition, the limitations of the working temperature borne by the elastic seat material at high temperatures must also be considered. The structural length and overall height of the butterfly valve is small, fast opening and closing speed, and has the fluid control characteristics, the principle of butterfly valve structure is suitable for making large calibre valves. When the butterfly valve is required to be used for flow control, it is important to choose the correct size and type of butterfly valve so that it can work properly and effectively.

Usually, in throttling, regulating control and slurry media, the structure is required to be short in length and fast in opening and closing speed (1/4 turn). Low-pressure cut-off (small differential pressure), the recommended choice of butterfly valve.

In the two-position adjustment, indented ground channel, low noise, cavitation and cavitation phenomenon, a small amount of leakage to the atmosphere, with abrasive media, you can choose the butterfly valve.

In special conditions of throttling adjustment, or require strict sealing, or wear and tear, low temperature (deep cold) and other conditions of use of butterfly valves, the need to use special design metal sealing with regulating devices, three eccentric or double eccentric special butterfly valves.

Butterfly valves are suitable for fresh water, sewage, seawater, salt water, steam, natural gas, food, pharmaceuticals, oil and various acids and alkalis and other pipelines that require complete sealing, zero leakage in gas test, high life expectancy, and working temperatures of -10 degrees to 150 degrees.

Soft seal eccentric butterfly valves are suitable for bidirectional opening and closing and regulation of ventilation and dust removal pipelines, and are widely used in metallurgy, light industry, electric power, petrochemical systems, such as gas pipelines and waterways.

Metal-to-metal line seal double eccentric butterfly valve is suitable for city heating, gas supply, water supply and other gas, oil, acid and alkali pipelines, as a regulating and throttling device.

Metal-to-metal face-sealed triple eccentric butterfly valve can be widely used in petroleum, petrochemical, chemical, metallurgy, electric power and other fields, in addition to being used as the procedure control valve of large-scale pressure change adsorption (PSA) gas separation device.

 5.What is the difference between double eccentric butterfly valve and other butterfly valves?

Table data from dombor.com

6.Double eccentric butterfly valve which common faults？

The rubber elastomer in double eccentric butterfly valve will be torn, worn, aged, perforated or even peeled off in continuous use. The traditional hot vulcanisation process is difficult to adapt to the needs of on-site repair, and the repair should be carried out with special equipment, consuming a lot of heat and electricity, which is time-consuming and labour-intensive. Nowadays, the polymer composite material is gradually used to replace the traditional method, with the adhesive force and excellent anti-wear, anti-tearing performance, to ensure that the repair to achieve the use of the cycle, shorten the downtime.

7.Double eccentric butterfly valve how to install and maintain

1、During installation, the valve flap should be stopped in the closed position.

2、Opening position should be determined by the rotation angle of the butterfly plate.

3、Butterfly valve with bypass valve should open the bypass valve before opening.

4、It should be installed according to the manufacturer's installation instructions. Butterfly valves with large weight should be set up with a firm foundation.

A.What are the precautions in the construction and installation of double eccentric butterfly valves?

1, the installation position, height, import and export direction must meet the design requirements, the connection should be firm and tight.

2, installed in the insulation pipeline on all types of manual valves, the handle shall not be down.

3, the valve must be installed before the appearance of the inspection, the valve nameplate should be in line with local national standards for the working pressure greater than 1.0 MPa and in the main pipeline to play a role in cutting off the valve, the installation should be carried out before the strength and tightness performance test, qualified before use. Strength test, the test pressure for the nominal pressure of 1.5 times the duration of not less than 5min, the valve shell, packing should be no leakage as qualified. Tightness test, the test pressure is 1.1 times the nominal pressure, to the valve sealing surface without leakage is qualified.

8.Double eccentric butterfly valve in the installation of what precautions

Double eccentric butterfly valve structure is simple, small size, light weight, its components are also relatively small, on the key several parts can constitute the butterfly valve, open the time is also very convenient, only need to choose the switch to ninety degrees can be, the butterfly valve on the fluid control is very good, you can increase the flow rate at any time or to reduce the flow rate, the valve in the transport of any fluid has a certain resistance, and the resistance of the butterfly valve is mainly from the resistance to its The resistance of butterfly valve mainly comes from itself, such as the thickness of the butterfly valve body, if you want to reduce the resistance to the fluid just need to reduce its thickness. The elastic seal has the defect of temperature limitation.

Butterfly valves are also used in a wide range of applications, if used to control the flow then you need to choose a different type and size of the valve body, because the butterfly valve in the design of its own more suitable for some of the larger calibre of the valve. Butterfly valve is not only widely used in oil, gas, chemical, water treatment and other general industry, but also used in thermal power plant cooling water system.

IMGV is a well-known manufacturer of butterfly valves, gate valves and check valves in China. We provide high quality valves. Currently the valves have been sold to more than 60 countries around the world. If you have enquiry please contact us for quotation, and professional technical support.