Pump with cutting wheel and pre-cutter

1. A pump comprising:

a cutting wheel,

a rotating shaft portion that projects axially from the cutting wheel and has an axis,

a pre-cutter driven by the shaft portion and having only first and second wings that extend radially from the shaft portion,

wherein the first and second wings have base portions with which the first and second wings adjoin a periphery of the shaft portion, with the base portions being offset relative to one another along the axis of the shaft portion,

wherein the first and second wings extend at different angles with respect to the axis of the shaft portion,

wherein said first and second wings are arranged and shaped such that, when seen in a projection onto a plane orthogonal to the axis of the shaft portion, they are symmetric under a rotation of 180° degrees about the axis of the shaft portion, and

wherein said first wing has the base portion thereof closer to a distal end of the shaft portion than the base portion of the second wing and forms an obtuse angle with the axis of the shaft portion, so that said first wing points axially away from the cutting wheel, and whereas the second wing forms an acute angle with the axis of the shaft portion so as to point toward the cutting wheel in an opposite direction from said first wing,

wherein each wing, when seen in a projection onto a plane orthogonal to the axis of the shaft portion, has a shape that is convexly curved in a direction of rotation of the shaft portion, and

further including a crest of stationary counter blades surrounding the pre-cutter and wherein free ends of the first and second wings move past the counter blades with a distance between the crest of counter blades and free ends of the first and second wings, when the pre-cutter rotates,

wherein the counter blades have a longitudinal axis that extends in parallel with the axis of the shaft portion, and each counter blade has a span along the longitudinal axis that is axially coextensive with at least a portion of each wing so that portions of each counter blade lie in a common radial plane with the free ends of both said wings so as to be in opposing relation to said free ends in a manner so as to crush any material between both wings and the counterblades as both wings rotate with the rotating shaft portion.

2. The pump according to claim 1 , wherein each wing has a leading edge and at its free end an outwardly angled catch that obstructs movement of chippings that slide along the respective leading edge.

3. The pump according to claim 1 , wherein the pump is configured to be disposed vertically in a collecting vessel so that the pre-cutter is disposed at a predetermined vertical distance from a bottom of the vessel and is facing the bottom of the vessel.