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Structure and sealing of butterfly valve

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butterfly valve-13

Development of butterfly valves

 

In the 1930s, the United States invented the butterfly valve, and it was introduced to Japan in the 1950s. It was only widely used in Japan in the 1960s, and it was promoted in China after the 1970s. At present, butterfly valves above DN300 mm have gradually replaced gate valves in the world. Compared with gate valves, butterfly valves have short opening and closing time, small operating torque, small installation space, and lightweight. Take DN1000 as an example, the butterfly valve is about 2T, and the gate valve is about 3.5T, and the butterfly valve is easy to combine with various driving devices, which has good durability and reliability.

The disadvantage of the rubber seal butterfly valve is that when it is used for throttling, cavitation will occur due to improper use, causing the rubber seat to peel off and damage. For this reason, metal-sealed butterfly valves have been developed internationally, and the cavitation zone has been reduced. In recent years, our factory has also developed metal-sealed butterfly valves. In recent years, Japan has also developed comb-tooth butterfly valves that are resistant to cavitation, low vibration, and low noise.

Under normal circumstances, the life of the general seal seat is 15-20 years for rubber seals and 80-90 years for metal seals. However, the correct selection depends on the requirements of the working conditions.

The relationship between the opening of the butterfly valve and the flow rate basically changes linearly. If it is used to control flow, its flow characteristics are also closely related to the flow resistance of the pipeline. For example, two pipelines are installed with the same valve diameter and form, but the pipeline loss coefficient is different, and the flow rate of the valve will also be very different.

If the valve is in a state with a large throttle range, the back of the valve plate is prone to cavitation, which may damage the valve. The correct use is to open more than 15°.

When the butterfly valve is in the middle opening, the opening shape formed by the valve body and the front end of the butterfly plate is centered on the valve shaft, and the two sides form different states. The front end of the butterfly plate on one side moves in the direction of the flowing water, and the other side moves against the direction of the flowing water. Therefore, one side of the valve body and the valve plate form a nozzle-like opening, and the other side is similar to a throttle opening. The nozzle side has a much faster flow rate than the throttle side, and negative pressure will be generated under the throttle side valve. The rubber seal may fall off.

The operating torque of the butterfly valve has different values ​​due to the different opening and closing directions of the valve. The horizontal butterfly valve, especially the large-diameter valve, due to the depth of water, the torque generated by the difference between the upper and lower water heads of the valve shaft cannot be ignored. In addition, when an elbow is installed on the inlet side of the valve, a bias flow is formed and the torque will increase. When the valve is in the middle opening, the operating mechanism needs to be self-locking due to the action of the water flow torque.

 

butterfly valve-1

 

Function of butterfly valve

 

Butterfly valve refers to a kind of whose closing part (disc or butterfly plate) is disc, which rotates around the valve shaft to achieve opening and closing. It mainly plays the role of cutting off and throttling on the pipeline.

The butterfly valve opening and closing part is a disc-shaped butterfly plate, which rotates around its own axis in the valve body to achieve the purpose of opening and closing or adjustment.

The butterfly valve is usually less than 90° from fully open to fully closed. The butterfly valve and the butterfly stem have no self-locking ability. For the positioning of the butterfly plate, a worm gear reducer should be installed on the valve stem. The use of worm gear reducer can not only make the butterfly plate have self-locking ability, make the butterfly plate stop at any position, but also improve the operational performance of the valve.

Industrial butterfly valve features: high-temperature resistance, high applicable pressure range, large nominal diameter of the valve, the valve body is made of carbon steel, and the sealing ring of the valve plate uses a metal ring instead of a rubber ring. Large high-temperature butterfly valves are manufactured by welding steel plates and are mainly used for flue ducts and gas pipes of high-temperature media.

 

butterfly valve-14

 

Five characteristics of butterfly valve

(1) Simple structure and small size. Due to its compact structure, short structure length, small size and lightweight, it is suitable for large diameters.
(2) The fluid resistance is small. When fully opened, the effective flow area of the valve seat channel is large, so the fluid resistance is small.
(3) The opening and closing are convenient and fast, the adjustment performance is good, the butterfly plate rotates 90. Both can complete the opening and closing. The flow can be controlled in stages by changing the rotation angle of the butterfly plate.
(4) The opening and closing moment is small because the discs on both sides of the rotating shaft are basically the same under the action of the medium, and the direction of the torque is opposite, so the opening and closing are more labor-saving.
(5) The low-pressure sealing performance is good, and the sealing surface material is generally rubber or plastic, so the sealing performance is good. Limited by the material of the sealing ring, the operating pressure and operating temperature range of the butterfly valve are relatively small. However, the working pressure and working temperature range of the hard seal butterfly valve have been greatly improved.

 

Three commonly used non-metallic sealing materials for butterfly valves

 

1. Nitrile rubber
Nitrile rubber is generally used as the seat material of butterfly valves, and its temperature resistance is not very good, so the manufactured butterfly valves are generally not used in high-temperature environments. But the abrasion resistance and deformation resistance of nitrile rubber are very good.

2. Ethylene Propylene Rubber
The temperature range of ethylene propylene rubber is similar to that of nitrile rubber, but the upper-temperature limit is ten to twenty degrees higher than that of nitrile rubber. It is also mainly used as a material for the seat of butterfly valves. Its advantages are good insulation performance, excellent ozone resistance, and no reaction with inorganic media. Therefore, butterfly valves made of ethylene-propylene rubber are generally used for the transportation of water and alcohol pipelines.

3. PTFE
PTFE has excellent temperature resistance and strong resistance to chemicals, which is commonly known as strong corrosion resistance. However, due to the special needs of some butterfly valves, PTFE will be improved and its insulation properties will be canceled so that the insulation properties of PTFE cannot be guaranteed.

 

Soft seal butterfly valve

 

The difference between hard seal butterfly valve and ordinary butterfly valve

 

In the eyes of general users, hard-sealed butterfly valves are generally driven by electric power, so they are used with electric actuators to form a pipeline control system. The ordinary butterfly valve is mostly manual. But in fact, in addition to electric, the hard-sealed butterfly valve can also be equipped with a turbine drive system or a pneumatic actuator. It can also be done if you want to manually drive the opening and closing.

The structure and main principle of the hard seal butterfly valve:

Hard-sealed butterfly valves are used in various fluid pipelines as a component for flow control and cut-off in pipelines, and their effects have been well received by users. Its main outstanding feature as a valve lies in its good sealing performance. The sealing structure of hard-sealed butterfly valves is mostly made of rubber or chemical polymers, and due to the characteristics of these materials, little effort is needed in the sealing structure. However, due to the characteristics of this type of material, hard-sealed butterfly valves are less used in high-temperature and high-pressure pipeline environments, and their corrosion resistance is relatively inferior to ordinary butterfly valves.

 

Step-by-step optimization of hard seal butterfly valve connection mode

 

At present, materials with relatively high hardness and certain corrosion resistance are generally the mainstream materials used in pipeline control valves. The resulting valve is also relatively durable. The hard seal butterfly valve is actually the best example. This is a valve device with a relatively small appearance, and its opening and closing method use an internal rotating shaft to drive the valve body opening and closing parts so that the internal opening and closing butterfly plate can rotate within a certain degree to realize the stable regulation of the medium in the pipeline. In fact, this adjustment is mainly to cut off the pipeline and adjust the flow of the medium.

Moreover, this type of butterfly valve has gradually changed into a valve device with a variety of connection methods. Among them, the butt-welded hard-sealed butterfly valve is currently used in some special environmental piping systems for height adjustment. Moreover, due to the sealing effect of welding and the processing of materials, this type of pipeline regulating valve can become a high-performance regulating valve to a certain extent. At present, this type of device can be highly effective for the regulation of pipelines. It is better than many other pipeline regulating valves in terms of durability.

 

Butterfly valve body WCB DN2000 PN25

 

Explosion-proof electric hard seal butterfly valve

 

Explosion-proof electric hard-sealed butterfly valve product description: The explosion-proof electric hard-sealed butterfly valve developed by our company. The double eccentric flange butterfly valve has compact structure, easy 90° rotary switch, reliable sealing, and long service life. It is widely used in water plants, power plants, and steel It is used as regulation and cut-off in the water supply and drainage of factories, papermaking, chemical industry, catering and other systems.

Features of explosion-proof electric hard seal butterfly valve:

1. The explosion-proof electric hard-sealed butterfly valve adopts a double eccentric structure, which has a tighter sealing function as it closes, and its sealing performance is reliable.

2. The sealing material is matched with stainless steel and nitrile oil-resistant rubber, which has a long service life.

3. The rubber sealing ring can be located on the valve body or on the butterfly plate, which can be applied to different characteristics of media for users to choose.

4. The butterfly plate adopts a frame structure with high strength, large flow area and small flow resistance.

5. The integral baking varnish can effectively prevent corrosion and can be used in different media as long as the sealing material of the sealing valve seat is replaced.

6. The explosion-proof electric hard-sealed butterfly valve has a two-way sealing function. It is not controlled by the flow direction of the medium during installation and is not affected by the spatial position. It can be installed in any direction.

 

FCV – Tieling Flow Control Valve Co., Ltd Is one of the key enterprises after the former Tieling Valve Works was reformed. It is the largest low-pressure big diameter valve, penstock manufacturing base. It has a history of more than 80 years, it is named as advanced new and high-tech enterprise. The main products: butterfly valve, gate valve, check valves, air release valve, rotating strainer, comb type cleaning machine, grating, steel penstock, cool and hot isolating gate, guarding gate, regulating shrinkage hole, inserting gate; the suitable medium: clean water, sewage water, sea water,air, high temperature stove air, gas, steam and different acid and alkali liquid; suitable temperature: -40℃ to 600℃;suitable pressure: 0.01Mpa~2.5Mpa;Nominal diameter:DN50-DN3000, actuating methods: manual, motor,pneumatic,hydraulic, motor& hydraulic. According to the customer’s requirements we can design and manufacture the products conforming to GB,JB,ISO,DIN,BS,API,ANSI. The products are widely used in water power plant, thermal power plant, water plant(city water supplying and distributing), sewage treatment plant,gas, airline, metallic, petroleum and chemical, mine, water power.

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