Apparatus and methods are described including manufacturing an impeller (152) by coupling a material (168) to a structure (165) that defines a plurality of helical elongate elements (166), such that the helical elongate elements (166) with the material (168) coupled thereto define one or more blades of the impeller (152). At least a portion of the structure (165) is dipped into the material (168) while the material (168) is in a liquid state. The material (168) is dried, while the material (168) is being supported by the plurality of helical elongate elements (166). During the drying of material (168), the structure is rotated about its longitudinal axis, such as to facilitate the formation of a film of the material (168) having a substantially uniform thickness within the impeller blade. Other applications are also described.
