Definition，characteristics and classification of butterfly valves

The definition of butterfly valve:

Butterfly valve is one kind of rotary valve which uses a disc-shaped closing member(which can be circular or rectangular,etc) to turn 90° or about 90° to open and close the valve. Butterfly valve is an ancient valve. In the early days, due to poor sealing performance of butterfly valves, it could only be used for flow adjustment. For example, flue valve is one kind of regulating butterfly valve. With the emergence of resilient sealing material such as synthetic rubber, and the in-depth study of sealing mechanisms, sealed butterfly valves have appeared. The emergence of resilient metal valve seats and new structural forms makes butterfly valves gradually adopted in high temperature and low temperature environments. The current development trend of butterfly valve is that they can be used for both adjustment and sealing. 

The characteristics of butterfly valve: 

Butterfly valve has advantages of simple structure, not easy to produce thermal deformation, light weight,small space occupation, relatively small resistance, rapid opening and closing, low opening and closing power, good sealing performance, long life,etc. So butterfly valve is widely used, especially in the large diameter, low pressure valves. In short, sealed butterfly valves are widely used in water systems and gas systems. Such as the water supply and drainage system of municipal engineering, various water supply systems, thermal pipe networks and sewage treatment systems of thermal power plants and nuclear power plants, water inlet valves of large turbines of hydro-power stations, electric power, chemical industry, petroleum, metallurgy, shipbuilding,paper making, city gas,etc.. butterfly valves have been used successively in water and sewage, food industry, nuclear energy and national defense projects, and there is a tendency to develop towards high and medium pressure. 

The mediums that butterfly valve can convey and control include various liquids such as water, condensed water, sewage, seawater, air, gas, and other gases and steam, dry powder, mud, fruit pulp and mixtures with suspended solids. At present, there are butterfly valves of class 600-1500. the the 1970s～1980s, our country also manufactured butterfly valve of PN40. at present, we have been able to manufacture butterfly valves with PN100 even higher pressure. The world’s largest butterfly valve measures 32ft(which is 9.75m); 

classification of butterfly valves: 

The sealing mechanism of valve is achieved by a certain sealing pressure acting on the sealing surface, and the butterfly valve is no exception. Generally speaking, the sealing of butterfly valve has three forms: 1. the specific pressure is generated by the interference. 2. press the sealing pair tightly by direct pressure or torque, such as double eccentric butterfly valve and triple eccentric butterfly valve, the sealing ring is filled with air or liquid. 3. by the poisson effect, the medium is pressed on the sealing ring. The larger the upstream and downstream pressure difference is,the easier the valve is to seal. 

There are many types of butterfly valves, according to application and effect, butterfly valve can be divided into cut-off type butterfly valve and adjustment type butterfly valve. 

According to structure form, butterfly valve can be divided into center line type butterfly valve, single eccentric butterfly valve, double eccentric butterfly valve, and triple eccentric type butterfly valve. 

According to sealing material, butterfly valve can be divided into rubber sealing butterfly valve, PTFE sealing butterfly valve, metal hard sealing butterfly valve.