Valve assembly

Claim 1

A valve assembly for closing and sealing an inlet which is full of large, granular, dry material, the valve comprising a housing defining the inlet and defining an outlet, the ratio of the outlet diameter to the inlet diameter being at least 1.5:1 thereby allowing unrestricted flow of large granular material through the housing, a closure member having the shape of a part of a spherical shell and being mounted for rotation between a first position in which the inlet is open and a second position in which the inlet is closed, the axis of rotation passing through the centre of the sphere of which the closure member forms a part, said centre lying close to the outlet whereby the ratio of the distance between the outlet and inlet of the valve to the inlet diameter is less than 1.5:1, said housing also defining an annular recess, a deformable, resilient sealing ring being mounted in said recess and secured to the defining surface of said recess except at a central portion thereof to prevent sliding movement of the sealing ring relative to the recess, means for supplying gas under pressure to said central portion of said recess so that gas supplied to said recess while the closure member is in its second position causes the centre of the sealing ring to deform out of the recess into engagement with the convex surface of the closure member to provide a gas-tight seal across the inlet, the sealing ring being sufficiently resilient to retract into the recess on release of gas pressure, and the housing having a shearing edge around the inlet which cooperates with a shearing edge provided on the closure member to shear granules of material located between said edges, the clearance between said edges being less than the clearance between the retracted sealing ring and the closure member to ensure that granules between the closure member and the sealing ring are not large enough to cause wear of the sealing ring, the sealing ring being sufficiently deformable to deform around any of the granules lodged between the sealing ring and the closure member to ensure said gas-tight seal.