Disclosed is a valve for use in particulate material processing. The valve has a rotatable closure member having a convex sealing surface and a resilient sealing ring moveable between a first configuration in which the sealing ring forms a seal around a circumference of the convex sealing surface; and a second position in which a circumferential gap is defined between the convex sealing surface and the sealing ring. The valve body defines a fluid-directing surface extending around the fluid passage between the inlet and the sealing ring to define an annular clearance which tapers towards the sealing ring and becomes narrower than the annular gap. When there is a pressure drop across the valve and before the closure member is moved to fully open the valve, material flowing through the valve experiences a dynamic pressure rise towards the circumferential gap, decreasing flow velocity and wear.