Abstract: A rotary air-lock feeder for a pneumatic conveying line includes the cylindrical housing with a straight bladed rotor mounted therein to propel materials from an upper inlet to a bottom discharge. The edges of the blades are positioned in close association with housing wall to prevent escape of air from the conveying line through feeder. A shear knife is mounted in housing with inner surface conforming to curvature of housing and a flat top surface intersecting inner surface to form a sharp cutting edge so as to shear material projecting beyond outer edge of rotor blades to prevent binding thereof between such outer edge and the housing wall.