Butterfly valve consists of disc rotating in trunnion bearings. In the open position the disc is edge-on, offering minimum resistance to flow. In the closed position it is rotated againt a seat.
Butterfly valves are available in size 25 mm to 6 m(1 in to 25 ft) diameter. They are particularly attractive because they take up little more room than the pipe flange. Infact some butterfly valves are designed specially for insertion between pipe flanges, using through bolts. These are know as wafer butterfly valve. Other types are nomally single-flanged or double-flanged, know also as lug-body valves.
Butterfly valve movement is simple and straightforward, requiring only 90 degree rotation of the butterfly for full movement (or somewhat less in most designs). The main disadvantage is that a simple butterfly design is difficult to render completely "tight" when closed, due to the absence of any wedging effect in this plane. This can be alleviated to a certain extent by seating the butterfly on a resilient ring on closure and/or offsetting the axis of rotation slightly so that, as well as rotating, as well as rotating, the blade has a movement in a plane at right angles to the spindle axis.
Butterfly valves are available in size 25 mm to 6 m(1 in to 25 ft) diameter. They are particularly attractive because they take up little more room than the pipe flange. Infact some butterfly valves are designed specially for insertion between pipe flanges, using through bolts. These are know as wafer butterfly valve. Other types are nomally single-flanged or double-flanged, know also as lug-body valves.
Butterfly valve movement is simple and straightforward, requiring only 90 degree rotation of the butterfly for full movement (or somewhat less in most designs). The main disadvantage is that a simple butterfly design is difficult to render completely "tight" when closed, due to the absence of any wedging effect in this plane. This can be alleviated to a certain extent by seating the butterfly on a resilient ring on closure and/or offsetting the axis of rotation slightly so that, as well as rotating, as well as rotating, the blade has a movement in a plane at right angles to the spindle axis.
