Abstract: A dosing unit for concentrate in a post-mix beverage dispenser is described which includes an enclosed cylinder space, and a pump piston with a bore running parallel with the axis. A control piston which is in contact with the input side shutoff of the cylinder space is disposed within and movable longitudinally of the bore in the pump piston. The control piston includes an intake opening, and in contact with the pump piston, forms an outlet opening, where the intake and the outlet openings are alternately opened or closed through axial movement of the control piston with respect to the cylinder space and the pump piston. The control piston movement is restricted with respect to the accelerator piston and constrained by axial impact points, so that an axial movement forced upon the control piston causes an impulse in both directions to open or close the intake or the outlet openings, after which by carry-over of the particular impact, the pump piston is moved axially the same distance.