(57) The present invention, there is provides a valve comprising a flexible sleeve having
first and second axially spaced sleeve portions 7, 8; first and second coaxially disposed,
relatively angularly movable rings 2, 16 relative to which the first and second sleeve
portions 7, 8 are respectively fixed; and means 1 for mounting the first and second
rings around an opening through which the flow of material is to be controlled by
the valve; wherein the first and second rings form parts of an epicyclic gear mechansim;
and wherein means 32,34 are provided for effecting angular movement of part of the
epicyclic gear mechanism between a first position corresponding to a fully closed
position of the valve and a second position corresponding to dully open position of
the valve, said epicyclic gear mechanism producing an increased angular relative movement
of the rings 2, 16 for a given angular movement produced by said angular movement
effecting means 32, 34.
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