Abstract: An orifice valve assembly which may be utilized to control the flow of a fluent material, such as powdered magnesium, propelled by gas under pressure, the valve controlling the flow in a linear manner.The valve includes a valve body having first and second adjacent concentric bores, the first bore being of a larger diameter than the second bore, and a cross-bore intersecting the first bore, the cross-bore having a cylindrical portion which intersects the first bore and frusto-conical inlet and outlet portions to either side of the cylindrical portion.