Dosing unit (1) for an ambulatory infusion device, comprising:a) a stationary member (2)b) a movable member(3),the movable member forming a charging valve to be open in a charging valve position of the movable member and a discharging valve to be open in a discharging valve position of the movable member,c) a plunger (50) in a metering cavity (31) of the movable member (30) and being adapted for displacement in the metering cavity (31) along an displacement axis (A),wherein the plunger (50) is adapted to couple to a driving unit and the movable member (30) is adapted to selectively couple to the driving unit, such that, by operating the driving unit with the movable member (30) being coupled, the movable member (30) may be moved with the plunger position along the displacement axis (A) being maintained and that, by operating the driving unit (505) with the movable member (50) being decoupled, the plunger (50) may be displaced with the position of the movable member (50) being maintained.Ambulatory infusion device comprising such a dosing unit.Method for operating a dosing unit for an ambulatory infusion device.
