Types and differences of butterfly valves, what are the characteristics of butterfly valves, and what should be paid attention to when selecting them?
Types and differences of butterfly valves:
Centerline butterfly valve, single eccentric butterfly valve, double eccentric butterfly valve and triple eccentric butterfly valve, these types of butterfly valves change the sealing and opening states by setting the position of the valve plate rotating axis.
Under the same circumstances, the rotation angle required for the valve plate to separate from the sealing ring when the valve is opened is smaller than the previous time, and the torque applied to the valve each time it is opened is greater than the previous time.
Three-eccentric butterfly valve: To be resistant to high temperature, hard seal must be used, but the leakage is large; to achieve zero leakage, soft seal must be used, but it is not resistant to high temperature. In order to overcome the contradiction of double-eccentric butterfly valve, the butterfly valve has been eccentric for the third time. The so-called third center means that the shape of the sealing pair is not a positive cone, but an oblique cone. The uniqueness of the three-eccentric butterfly valve is that the valve equipped with the butterfly plate is installed with a three-section shaft structure. The two shaft sections of the three-section shaft valve stem are concentric, and the center line of the middle section shaft deviates from the axis at both ends. The butterfly plate is installed on the middle shaft section. Such an eccentric structure makes the butterfly plate 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, it moves a distance into the sealing cone surface of the valve seat, and the sealing surface of the butterfly plate and the valve seat coincide to achieve a reliable seal.
Double eccentric butterfly valve: It is a further improvement on the single eccentric butterfly valve, which is the most widely used double eccentric butterfly valve. Its structural feature is that the valve stem axis deviates from the center of the butterfly plate and the center of the valve body. The double eccentric action allows the butterfly plate to quickly separate from the valve seat after the valve is opened, greatly eliminating unnecessary excessive extrusion and scratches between the butterfly plate and the valve seat, reducing opening resistance, reducing wear, and improving valve efficiency and valve seat life.
Single eccentric butterfly valve: 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 produced. Its structural feature is that the valve stem axis deviates from the center of the butterfly plate, so that the upper and lower ends of the butterfly plate no longer rotate, and the center of the butterfly plate axis is dispersed, reducing the excessive extrusion between the upper and lower ends of the butterfly plate and the valve seat.
The structural characteristics of the centerline butterfly valve are that the valve stem axis, the center of the butterfly plate, and the center of the valve body are in the same position. Since the butterfly plate and the valve seat are always in a state of extrusion and scraping, the resistance distance is large and the wear is fast. The structure is simple and convenient. In order to overcome extrusion and scraping and ensure sealing performance, the valve seat is basically made of elastic materials such as rubber or polytetrafluoroethylene.
The butterfly valve can be quickly opened and closed by rotating 90°, and has the advantages of light weight and small structure size (especially the wafer-type butterfly valve). However, its sealing reliability is relatively poor, so it is often used in industrial production equipment under medium and low pressure and medium and low temperature medium conditions. With the large-scale petrochemical production equipment, it is an inevitable trend to replace gate valves with butterfly valves. Due to the emergence of double eccentric high-performance butterfly valves and triple eccentric metal hard seal butterfly valves, the problems of thermal expansion compensation and wear compensation have been better solved. Therefore, butterfly valves have gradually begun to be used in harsher medium conditions.
(1) Classification by structural form
1. Center seal butterfly valve
2. Single eccentric sealing butterfly valve
3. Double eccentric sealing butterfly valve
4. Triple eccentric sealing butterfly valve
(2) Classification by link method
1. Wafer butterfly valve
2. Flange butterfly valve
3. Leg type butterfly valve
4. Welding butterfly valve