Abstract Rotary feeders are one of the most widely used devices for regulating the flow of powdered and granular solid materials from storage facilities such as hoppers, silos, bins and bunkers. In this paper the performance characteristics of such feeders are examined, from both model and experimental standpoints, with a view to enhancing understanding of the operation of these devices. Through understanding the way in which materials flow through the inlet port and into the rotor pockets a model is developed that describes how the feed rate varies with the rotor speed. Experimental work confirms the general form of the characteristics predicted by the model studies. An approach is developed for predicting the feed rate characteristics when handling free-flowing materials having particle sizes greater than 5 mm. Further work is necessary to predict these characteristics when handling materials have particles smaller than this size.