A dosing system that performs mass control of a dosed amount of liquid product introduced into a chamber of an internal mixer that performs rubber mixing processes, the dosing system comprises: - at least one reservoir that stores a liquid product between a minimum level (N MIN) and a maximum level (N MAX) wherein a sensor controls the level of liquid product arriving at the reservoir between the minimum level (N MIN) and the maximum level (N MAX) therein; - at least one product conduit of a predetermined diameter that conveys a dosed amount of liquid product from the reservoir to the internal mixer; - a dosing means that directly measures a mass and density of a liquid product dosed from the reservoir and conveyed to the internal mixer, the dosing means comprising: - at least one pump disposed downstream of the reservoir, the pump having a variable speed in accordance with an intended liquid product dosage; and - a mass flow meter arranged downstream of the pump; - a mixing injector disposed downstream of the dosing means for introducing different liquid products from a mixed rubber mixture into an internal mixer chamber in which the mixing injector is mounted, with a first switching valve that directs a liquid product measured by the dosing means to the mixing injector; - a pressure sensor installed downstream of the dosing means to detect the pressure of a dosing circuit comprising the product conduit, the reservoir, the dosing means and the mixing injector and - a non-return valve installed upstream of the dosing means in order to maintain the dosing system under pressure at the end of a dosing cycle carried out by the dosing system; the dosing system is characterized in that: - at least one conveyance conduit that conveys the liquid product from a source of the liquid product corresponding to the reservoir, the conveyance conduit terminating at an outlet that descends below the minimum level (N MIN) of liquid product stored in the reservoir. - at least one reservoir that stores a liquid product between a minimum level (N MIN) and a maximum level (N MAX) wherein a sensor controls the level of liquid product arriving at the reservoir between the minimum level (N MIN) and the maximum level (N MAX) therein; - at least one product conduit of a predetermined diameter that conveys a dosed amount of liquid product from the reservoir to the internal mixer; - a dosing means that directly measures a mass and density of a liquid product dosed from the reservoir and conveyed to the internal mixer, the dosing means comprising: - at least one pump disposed downstream of the reservoir, the pump having a variable speed in accordance with an intended liquid product dosage; and - a mass flow meter arranged downstream of the pump; - a mixing injector disposed downstream of the dosing means for introducing different liquid products from a mixed rubber mixture into an internal mixer chamber in which the mixing injector is mounted, with a first switching valve that directs a liquid product measured by the dosing means to the mixing injector; - a pressure sensor installed downstream of the dosing means to detect the pressure of a dosing circuit comprising the product conduit, the reservoir, the dosing means and the mixing injector and - a non-return valve installed upstream of the dosing means in order to maintain the dosing system under pressure at the end of a dosing cycle carried out by the dosing system; the dosing system is characterized in that: - at least one conveyance conduit that conveys the liquid product from a source of the liquid product corresponding to the reservoir, the conveyance conduit terminating at an outlet that descends below the minimum level (N MIN) of liquid product stored in the reservoir. - at least one pump disposed downstream of the reservoir, the pump having a variable speed in accordance with an intended liquid product dosage; and - a mass flow meter arranged downstream of the pump; - a mixing injector disposed downstream of the dosing means for introducing different liquid products from a mixed rubber mixture into an internal mixer chamber in which the mixing injector is mounted, with a first switching valve that directs a liquid product measured by the dosing means to the mixing injector; - a pressure sensor installed downstream of the dosing means to detect the pressure of a dosing circuit comprising the product conduit, the reservoir, the dosing means and the mixing injector and - a non-return valve installed upstream of the dosing means in order to maintain the dosing system under pressure at the end of a dosing cycle carried out by the dosing system; the dosing system is characterized in that: - at least one conveyance conduit that conveys the liquid product from a source of the liquid product corresponding to the reservoir, the conveyance conduit terminating at an outlet that descends below the minimum level (N MIN) of liquid product stored in the reservoir. - at least one conveyance conduit that conveys the liquid product from a source of the liquid product corresponding to the reservoir, the conveyance conduit terminating at an outlet that descends below the minimum level (N MIN) of liquid product stored in the reservoir.