Working principle of butterfly valve:
Butterfly valve is a valve that uses a disc-type opening and closing part to rotate back and forth about 90° to open, close or adjust the flow of the medium. Butterfly valves not only have simple structure, small size, light weight, low material consumption, small installation size, small driving torque, easy and rapid operation, but also have good flow regulation function and closing sealing characteristics at the same time. They are the latest development in the past ten years. One of the fastest valve varieties.
Butterfly valves are widely used. The variety and quantity of its use are still expanding, and are developing towards high temperature, high pressure, large diameter, high sealing, long life, excellent regulating characteristics, and multi-function in one valve. Its reliability and other performance indicators have reached a high level.
Butterfly valve characteristics:
1. The butterfly valve has the characteristics of simple structure, small size, light weight, low material consumption, small installation size, rapid switching, 90° reciprocating rotation, and small driving torque. It is used to cut off, connect, and regulate the medium in the pipeline. Has good fluid control characteristics and shut-off sealing performance.
2. The butterfly valve can transport mud and minimize the accumulation of liquid at the pipe mouth. At low pressure, a good seal can be achieved. Good adjustment performance.
3. The streamlined design of the butterfly plate reduces fluid resistance loss, making it an energy-saving product.
4. The valve stem is a through-stem structure. After quenching and tempering treatment, it has good comprehensive mechanical properties, corrosion resistance, and scratch resistance. When the butterfly valve opens and closes, the valve stem only rotates and does not move up and down.
The packing of the valve stem is not easily damaged and the sealing is reliable. It is fixed with the taper pin of the butterfly plate, and the extended end is designed to prevent the valve stem from collapsing when the connection between the valve stem and the butterfly plate breaks accidentally.
5. The connection methods include flange connection, clamp connection, butt welding connection and lug clamp connection.
The driving forms include manual, worm gear transmission, electric, pneumatic, hydraulic, electro-hydraulic linkage and other actuators, which can realize remote control and automatic operation.
Advantages of butterfly valve:
1. Opening and closing is convenient, fast, labor-saving, has small fluid resistance, and can be operated frequently.
2. It has simple structure, small external dimensions, short structural length, small volume and light weight, and is suitable for large-diameter valves.
3. Can transport mud with minimal liquid accumulation at the pipe mouth.
4. Under low pressure, good sealing can be achieved.
5. Good adjustment performance.
6. When fully open, the effective flow area of the valve seat channel is larger and the fluid resistance is smaller.
7. The opening and closing torque is small. Since the butterfly plates on both sides of the rotating shaft are basically equally affected by the medium and the torque is generated in opposite directions, opening and closing is less labor-intensive.
8. The sealing surface material is generally made of rubber or plastic, so the low-pressure sealing performance is good.
9. Easy to install.
10. The operation is flexible and labor-saving, and manual, electric, pneumatic and hydraulic modes can be selected.
Butterfly valves can be divided into four categories according to structural differences: center butterfly valve, single eccentric butterfly valve, double eccentric butterfly valve and triple eccentric butterfly valve. Under what circumstances are they applicable?
Overview of butterfly valve:
Center butterfly valve, single eccentric butterfly valve, double eccentric butterfly valve and triple eccentric butterfly valve actually reflect a process of opening and closing that is becoming more and more labor-saving, and the sealing surface wear is getting smaller and smaller. By setting the position of the rotating shaft of the butterfly valve plate, the sealing and opening status of the butterfly valve is changed. Under the same conditions, the valves receive greater torque at each opening than the other. When the valve is opened, the angle required for the valve plate to separate from the seal is smaller than the other.
Center butterfly valve:
The structural feature of the center butterfly valve is that the valve stem axis, butterfly plate center, and valve body center are at the same position. Generally speaking, in principle, if you can use the center butterfly valve, try to use the center butterfly valve. Because the central butterfly valve does not require high sealing performance in terms of structure or operation, it is a conventional product. In order to overcome extrusion and scratching and ensure sealing performance, the seat of the center butterfly valve is basically made of elastic materials such as rubber or polytetrafluoroethylene, which is a soft-sealing butterfly valve. This makes the central butterfly valve subject to temperature restrictions in use. In order to solve the extrusion problem between the butterfly plate and the valve seat of the concentric butterfly valve, a single eccentric butterfly valve was also produced. Its structural feature is that the axis of the valve stem deviates from the center of the butterfly plate.
Double eccentric butterfly valve:
Double eccentric butterfly valve is the most widely used. Its structural feature is that the axis of the valve stem is deviated from the center of the butterfly plate and the center of the valve body. It deviates from the two center positions, so it is called a double eccentric butterfly valve. Many double eccentric butterfly valves have line seals. When the sealing surface is closed, friction occurs between the disc and the valve seat, and the sealing effect is very good. It has the characteristics of small area and strong pressure. After the valve is opened, the butterfly plate can quickly separate from the valve seat, which greatly eliminates unnecessary excessive extrusion and scratching between the butterfly plate and the valve seat, reduces the opening resistance, reduces wear, and increases the service life of the valve seat.
Triple offset butterfly valve:
The triple eccentric butterfly valve has a third eccentricity on the basis of the double eccentric butterfly valve. The shape of the sealing pair is not a forward cone, but an oblique cone. Mostly short distance force and face seals. The valve stem shaft of the triple eccentric butterfly valve is a three-section shaft structure. The two shaft sections of the three-section shaft valve stem are concentric, and the center line of the center section shaft is offset from the two end axes by a center distance, and the butterfly plate is installed in the middle. on the shaft segment. Such an eccentric structure makes the butterfly plate become double eccentric when it is in the fully open position, and becomes single eccentric when the butterfly plate rotates to the closed position. Due to the effect of the eccentric shaft, when it is close to closing, the butterfly plate moves a certain distance into the sealing cone surface of the valve seat, and the sealing surface of the butterfly plate and the valve seat matches to achieve reliable sealing performance. It makes up for the contradiction that hard seals have poor sealing, while soft seals have good sealing effects but are not resistant to high temperatures.
Butterfly valve is suitable for:
1. Usually, in throttling, regulating control and mud media, it is required to have a short structure length and fast opening and closing speed (1/4 turn). For low pressure cut-off (small pressure difference), butterfly valve is recommended.
2. Butterfly valves can be used when there are double-position adjustments, constricted channels, low noise, cavitation and vaporization, a small amount of leakage into the atmosphere, and abrasive media.
3. When the butterfly valve is used for throttling adjustment under special working conditions, strict sealing is required, or the butterfly valve is used under severe wear, low temperature (cryogenic) and other working conditions, it is necessary to use a specially designed metal sealing belt adjustment device with triple eccentricity or double eccentricity. Special butterfly valve.
4. Butterfly valves are suitable for fresh water, sewage, sea water, salt water, steam, natural gas, food, medicine, oil and other products that require complete sealing, zero gas test leakage, high life requirements, and operating temperatures between -10 degrees and 150 degrees. Various acid-base and other pipelines.
5. Soft-sealing eccentric butterfly valves are suitable for bidirectional opening, closing and adjustment of ventilation and dust removal pipelines. They are widely used in gas pipelines and waterways in metallurgy, light industry, electric power, and petrochemical systems.
6. Metal-to-metal wire sealed double eccentric butterfly valve is suitable for urban heating, gas supply, water supply and other gas, oil, acid and alkali pipelines, etc., as a regulating and throttling device.
7. In addition to being used as a program control valve for large-scale pressure swing adsorption (PSA) gas separation devices, metal-to-metal surface sealing triple eccentric butterfly valves can also be widely used in petroleum, petrochemical, chemical, metallurgy, electric power and other fields. They are gate valves and globe valves. A good alternative product.
