What are single eccentric and double eccentric in butterfly valves? What's the difference, please explain in detail?
Eccentric butterfly valve is divided into single eccentric butterfly valve, double eccentric butterfly valve, three eccentric butterfly valve, variable eccentric butterfly valve.Single eccentric butterfly valve: extrusion problems, address concentric butterfly valve and valve seat of the resulting in a single eccentric butterfly valve, the structural characteristics of the stem axis deviated from the disc center, so that the butterfly is no longer a rotary bottom plate, axial dispersion, reduce the excessive squeezing and the lower end of the seat of the butterfly board.
Double eccentric butterfly valve: in the single eccentric butterfly valve on the basis of further improvement of forming, is the most widely used double eccentric butterfly valve. The structure features that the center of the stem deviates from the center of the disc as well as the center of the body. The effect of the double eccentric valve can be opened immediately after the disc from the valve seat, substantially eliminating the unnecessary disc and valve seat over squeezing, scratching phenomenon, reduce the resistance from the open, reducing the wear and improve seat life.
Three eccentric butterfly valve: to high temperature, must use hard seal, but the leakage is large; to zero leakage, must use soft sealing, but not high temperature. In order to overcome the double eccentric butterfly valve this contradiction, and the butterfly valve for third times eccentric. The so-called third eccentric, that is, the shape of the sealing pair is not a positive cone, but rather oblique cone.Variable eccentric butterfly valve: variable eccentric butterfly valve is unique in that the valve stem axis installation disc is a three shaft type structure, the three stem shaft two concentric shafts, while the center section of the shaft center line and both ends of a center axis deviation distance, the installation disc in the middle section of the shaft. The eccentric structure makes the disc become double eccentric at full open position, and becomes eccentric when the disc rotates to the closed position. Due to the action of the eccentric shaft, near the close, the butterfly plate sealed to the seat by moving a distance within the cone, the butterfly plate and the valve seat sealing surface to achieve consistent and reliable sealing performance.
