Abstract: An impeller for a centrifugal pump has an axis of rotation. The impeller includes a pair of covers which cooperate to define a chamber, and blades in the chamber defining generally radial flow channels. Each of the covers has a wall which is oriented transverse to the axis of rotation. The walls are provided with cutouts at the periphery of the impeller and one cutout is associated with each flow channel. The radial lengths of the cutouts are equal to or less than one-half the lengths of the flow channels. Each flow channel and its respective cutout cooperate to define an aperture which opens to the exterior of the chamber both axially and radially.