Distribution member for varying the flow rate for a pump

The variable volumetric flow device has a first component (1) with an inlet opening (5) coupled to an inlet (4) and a second coaxial component with at least 2 outlet openings (6a,6b) lying in a common plane, each connected to an outlet coupled to the pump. The coaxial components can slide relative to one another to bring the inlet opening into alignment with the outlet openings, one of the components rotated in synchronism with the pump, the other component remaining stationary.