The invention relates to a plastic metering system in a device for producing plastic articles, comprising a metering unit (1) forming a block (2) comprising a material feed duct (10), a metering cavity (4) which may communicate with the said material feed duct (10), a material outlet orifice (5) placed on a wall of the said metering cavity (4), and a valve (3) in the form of a cylindrical rod designed to slide through and close off the said material outlet orifice (5), characterized in that the metering unit (1) furthermore includes a piston (7) mounted so as to slide coaxially around the valve (3) so as to allow the volume of the metering cavity (4) to be varied and the material feed duct (10) to be momentarily closed off. The invention also relates to a method for using the said system.