The invention relates to a pumping system for producing a volume flow of dialysis solution in a dialysis machine, the pumping system comprising at least one piston pump, the piston of which co-operates with a working fluid which in turn exerts a force on a conveyor means, in particular a membrane. Adjustment means are provided, by which the conveying volume of the piston pump per piston stroke can be reduced. The adjustment means comprise a mechanical piston stop, which can be varied in position, for reducing the piston stroke and/or means for reducing the amount of the working medium and/or means for reducing the volume of the conveying chamber which co-operates with the conveying means and contains the dialysis solution to be conveyed.
