The definition, classification of butterfly valves

A butterfly valve is a rotary valve which is open or closed by rotating a disk-shaped, circular or rectangular closure member for about 90 or 90 degrees. The butterfly valve is an old valve. It was only used for adjustment in the early stage due to its poor sealing performance. For example, the flue valve is an adjustment butterfly valve. With the advent of elastomeric sealing materials such as synthetic rubber and the in-depth study of sealing mechanisms, sealing butterfly valves have emerged. The emergence of elastic metal valve seats and new structural forms has led to the adoption of butterfly valves in high and low temperature environments. At present, the development trend of butterfly valves is both for adjustment and sealing.

The butterfly valve has the advantages of simple structure, less heat deformation, light weight, relatively low resistance, quick opening and closing, low opening and closing power, good sealing performance, long service life and having small space, so it is widely applied, especially at low pressure large diameter valves. In short, sealing butterfly valves are widely applied to water systems and gas systems. Butterfly valves have been largely used in fields including water supply and drainage systems of municipal engineering, various water supply systems of thermal power plants and nuclear power plants, heat-supply pipe networks and sewage treatment systems, water inlet valves for large water turbines, chemical industry, petroleum, metallurgy, shipbuilding, papermaking, urban gas and food industries, atomic energy and national defense projects. And butterfly valves have a development trend towards high and medium pressure. The medium that can be transported and controlled by the butterfly valve includes various liquids such as water, condensed water, sewage, seawater, gas like air and coal gas, steam, dry powder, mud, pulp and mixtures with suspended solids. There are currently butterfly valves of Class 600~1500. In the 1970s and 1980s, China also manufactured butterfly valves with a class rating of PN40. At present, China already has the ability to manufacture butterfly valves of PN100 or higher pressure. The world’s largest butterfly valve has the size of 32ft (9. 75m).
  
The sealing mechanism of the butterfly valve is achieved by certain sealing pressure on the sealing surface, and the butterfly valve is no exception. The sealing of the butterfly valve generally can be classified into three different kinds.
1. Sealed by specific pressure generated by magnitude of interference.
2. The sealing pair is pressed by direct pressure or torque, like Double Offset Butterfly Valves and Triple Offset Butterfly Valves.
3. The medium is pressed against the seal ring by the Poisson effect. The larger the pressure difference between the upstream and downstream is, the easier the seal becomes. 
 
Butterfly valves can be classified according to various methods. For example, butterfly valves can be divided into cut-off type and adjustment type according to their usage and function; they can be divided into Concentric butterfly valves, double offset butterfly valves and triple offset butterfly valves according to their structure. They can be divided into rubber sealing  butterfly valves, PTFE sealing butterfly valves and metal sealing butterfly valves according to their sealing materials.

Flange butterfly valve by way of classification:
1. Clip on butterfly valve: butterfly valve on the butterfly plate installed in the pipe diameter direction. In the body of the butterfly valve in the cylindrical channel, disc shaped plate around the axis of rotation, the rotation angle of 0 degrees -90 degrees, when rotated to 90 degrees, the valve is in full open state. The butterfly valve has the advantages of simple structure, small size and light weight. Besides, the utility model has the advantages of simple operation and simple operation, and the valve can be opened and rotated at 90 DEG. Butterfly valve in the fully open position, the disc thickness is the only medium through the body resistance, so the pressure drop through the valve is very small, with good flow control characteristics.
2. Flange type butterfly valve, flanged butterfly valve for vertical plate structure, stem seal integral metal seal valve for flexible graphite plate and stainless steel plate composite structure, is mounted on the valve body and disc sealing surface surfacing welding of stainless steel. Soft sealing valve sealing ring for nitrile rubber material, is installed in the butterfly board. Flange type soft sealing butterfly valve
3. Lug type butterfly valve:
4. Welding type: butterfly valve is a non sealed butterfly valve, widely used in building material, metallurgy, mining, electricity and other production process of medium temperature are less than 300 of nominal pressure for 0.1Mpa pipeline, to connect, open and close or adjust the medium quality.

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