An injector for introducing different liquid products of a rubber mixture into a chamber of an internal mixer in which the injector is mounted, the injector comprising: - a cylindrical housing of a predetermined length between an injection end and an opposite end of the injector, the housing comprising an injection conduit dedicated to the flow of a liquid product to form the mixture, the injection conduit extending between an outlet of the injection conduit, which is coextensive with the injection end of the housing, and an opposite inlet, and the injection conduit comprising a seat defined adjacent to the outlet; - a valve disposed in the injection conduit that meters a corresponding liquid product, the valve comprising a longitudinal stem that extends between a tail disposed adjacent the inlet of the injection conduit and a head disposed adjacent the seat of the injection conduit; - a return spring disposed around the stem of the valve that controls a sliding movement of the valve relative to the injection conduit between a closed position, where the head engages the seat and blocks the outlet of the injection conduit, and an open position, where the head no longer engages the seat and unblocks the outlet of the injection conduit; - an injection device integrated with the housing and comprising a supply conduit that delivers a liquid product to a corresponding injection conduit from a reservoir in which the liquid product is stored, each supply conduit being arranged perpendicularly to a corresponding injection conduit to introduce the liquid product to the inlet of the injection conduit; the injector is characterized in that - the housing comprises at least two injection conduits and in that - a temperature control circuit is inside the injector. - a cylindrical housing of a predetermined length between an injection end and an opposite end of the injector, the housing comprising an injection conduit dedicated to the flow of a liquid product to form the mixture, the injection conduit extending between an outlet of the injection conduit, which is coextensive with the injection end of the housing, and an opposite inlet, and the injection conduit comprising a seat defined adjacent to the outlet; - a valve disposed in the injection conduit that meters a corresponding liquid product, the valve comprising a longitudinal stem that extends between a tail disposed adjacent the inlet of the injection conduit and a head disposed adjacent the seat of the injection conduit; - a return spring disposed around the stem of the valve that controls a sliding movement of the valve relative to the injection conduit between a closed position, where the head engages the seat and blocks the outlet of the injection conduit, and an open position, where the head no longer engages the seat and unblocks the outlet of the injection conduit; - an injection device integrated with the housing and comprising a supply conduit that delivers a liquid product to a corresponding injection conduit from a reservoir in which the liquid product is stored, each supply conduit being arranged perpendicularly to a corresponding injection conduit to introduce the liquid product to the inlet of the injection conduit; the injector is characterized in that - the housing comprises at least two injection conduits and in that - a temperature control circuit is inside the injector.