butterfly valves are attractive
Butterfly Valves 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.
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