Butterfly valve, also called as flap valve is a valve that has simple structure, used for media having low pressure. The closure member of butterfly valve is a disc which can swing along with valve shaft. Operation is similar to that of a ball valve, which allows for quick shut off. A butterfly valve is from a family of valves called quarter-turn valves. In operation, the valve is fully open or closed when the disc is rotated a quarter turn. There are different kinds of butterfly valves, adapted for different pressures and different usage.


Based on materials used for sealing face, butterfly valve is classified into soft sealing butterfly valve, hard sealing butterfly valve.


Based on types of sealing, butterfly valve is classified into forced sealing butterfly valve, pressurized sealing butterfly valve and automatic sealing butterfly valve. 


Based on working pressure, butterfly valve is classified into vacuum butterfly valve, low pressure butterfly valve, medium pressure butterfly valve, high pressure butterfly valve and ultra-high pressure butterfly valve.

Based on connection, butterfly valve is classified into wafer butterfly valve, flanged butterfly valve, lug type butterfly valve and welded butterfly valve.

 

Butterfly valve is a simple structure of the regulating valve, can be used for low pressure pipe medium switch control butterfly valve refers to the closing part (disc or butterfly disc) as a disc, rotating around the valve shaft to achieve the opening and closing of a valve.

 

Valves can be used to control the flow of various types of fluids such as air, water, steam, various corrosive media, mud, oil, liquid metal and radioactive media. It mainly used for cutting and throttling the fluids on the pipeline. Butterfly valve has a  disc-shaped disc in the valve body,and this disc rotating around its own axis ,to achieve the purpose of opening and closing or adjustment.

 

Development history


In the 1930s, the United States invented the butterfly valve, introduced into Japan in the 1950s, and in China, the promotion was after the 1970s. The main characteristics of butterfly valve are: small operating torque, small installation space and light weight. Take DN1000 as an example, the butterfly valve is about 2 T, and the gate valve is about 3.5 T, and the butterfly valve is easy to combine with various driving devices, which has good durability and reliability. The disadvantage of rubber seal butterfly valve is that when used for throttling, it will produce cavitation erosion due to improper use, which will cause spalling and damage of rubber seat,so how to choose a suitable batterfly valve seal should according to the requirement of the project. The relationship between the opening degree and the flow rate of the butterfly valve is basically linear proportional change. If it is used to control the flow rate, its flow characteristics are also closely related to the flow resistance of the pipe, for example  it two pipes have the same caliber and form to install the valves,the valves flow can has big difference if the loss coefficient of the pipes are different,.If the valve is in a large throttling state, the back of the valve disc is prone to cavitation, there is the possibility of damage to the valve, so generally used over 15°.  

 

Structure

 

Mainly consists of valve body, stem, disc and sealing ring.

 

Characteristics

 

1. butterfly valve has the characteristics of simple structure, small volume, light weight, less material consumption, small installation size, fast switch ,90° reciprocating rotation, small driving torque and so on. it is used to cut off, turn on and adjust the medium in the pipeline. it has good fluid control characteristics and close sealing performance.

 

2. butterfly valve can transport mud, at the pipe mouth accumulated the least liquid. Can achieve good sealing in low pressure,has good adjustment performance.

 

3. butterfly valve disc is streamline design, so that fluid resistance loss is small, it is an energy-saving product.

 

4. stem is a through rod structure, after tempering treatment, has good comprehensive mechanical properties and corrosion resistance, scratch resistance. When opening or closing the butterfly valve, the stem is operated only by rotating motion but not by lifting,the packing of stem is not easy to be damaged.

 

Types of Butterfly valves:

 

1.According to the structure form,butterfly valve can be divided into offset type,triple offset type,double offset type.

2.According to the driving forms,butterfly valves can be divided into Electric butterfly valve, Pneumatic butterfly valve,Hydraulic butterfly valve, Manual butterfly valve.

3.According to the seal form can be divided into soft seal type and hard seal type two. The soft seal type is generally sealed by rubber ring, and the hard seal type is usually sealed by metal ring.


4.According to working pressure:

(1) Vacuum butterfly valve. butterfly valve with working pressure lower than standard stack atmospheric pressure.

 

(2) Low pressure butterfly valve. butterfly valve with nominal pressure PN<1.6 MPa.

 

(3) Medium pressure butterfly valve. butterfly valve with nominal pressure PN of 2.5--6.4 MPa.

 

(4) High pressure butterfly valve. Butterfly valve with nominal pressure PN MPa 10.0-80.0.

 

(5) Ultrahigh pressure butterfly valve. butterfly valve with nominal pressure PN>100 MPa.

 

5.According to working temperature:

(1) High temperature. t>450°C butterfly valve.

 

(2) Medium temperature butterfly valve. 120C<t<450℃ butterfly valve.

 

(3) Normal temperature butterfly valve. one 40 C<t<120°C butterfly valve.

 

(4) Low temperature butterfly valve. one 100<t< one 40°C butterfly valve.

 

(5) Ultra-low temperature butterfly valve. t<100°C butterfly valve.

 

6.According to connectiontypes:

1. wafer type butterfly valve

2.flanged butterfly valve

3.lug butterfly valve

4. welded butterfly valve


Butterfly valve simple structure, small size, light weight, its components are also relatively small, opening is also very convenient, only need to switch to 90 degrees. butterfly valve has a good performance to the fluid control, can increase or reduce the flow rate at any time.

 

Butterfly valve is also a wide range of applications.They are not only widely used in oil, gas, chemical industry, water treatment and other general industries, but also used in the cooling water system of thermal power stations.


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