the present invention is a pumping system which mixes liquids with a well - controlled proportioning and flow rate . the pumping system according to the invention comprises a liquid mixing device placed upstream from a pump . the liquids are taken from vessels , cyclically introduced , in a determined proportion , in a mixing chamber through alternate opening of on - off solenoid valves . the system is controlled at the input by using a damping means such as bellows in antechambers in order to avoid the effects of velocity discontinuities at the time of the opening and of the closing of the valves . the delivery of pump is controlled at the input as well as at the discharge end . the system may be used for liquid chromatography plants .