The present invention relates to an aerosol-generating system comprising a liquid storage portion for storing liquid aerosol-forming substrate, wherein the liquid storage portion comprises a movable wall and an outlet, a vaporiser comprising a heating element having a structure defining an open-ended internal passage for heating deposited liquid aerosol-forming substrate, a pump configured for delivering liquid aerosol-forming substrate from the outlet of the liquid storage portion to the internal passage of the heating element, the pump comprising a micro stepper motor with a drive shaft that is configured to rotate for a predetermined amount upon performing one step of the micro stepper motor, a piston connected to the movable wall, and a lead screw connecting the drive shaft to the piston and configured to translate a rotation of the drive shaft into an axial movement of the piston and a corresponding axial movement of the movable wall, wherein the vaporiser is configured for heating the delivered liquid aerosol-forming substrate in the internal passage to a temperature sufficient to volatilize at least a part of the delivered liquid aerosol-forming substrate. The present invention further relates to a cartridge for an aerosol-generating system, wherein the cartridge comprises the liquid storage portion, the piston, and the lead screw. The present invention further relates to a method for generating aerosol.La presente invención se refiere a un sistema generador de aerosol que comprende una porción de almacenamiento de líquido para almacenar un sustrato líquido formador de aerosol, en donde la porción de almacenamiento de líquido comprende una pared móvil y una salida, un vaporizador que comprende un elemento de calentamiento que tiene una estructura que define un pasaje interno de extremo abierto para calentar el sustrato líquido formador de aerosol depositado, una bomba configurada para suministrar el sustrato líquido formador de aerosol de la salida de la porc
