Abstract: It comprises a metering valve (11) mounted inside a body (12) provided with an inlet (13) and an outlet (14). The inlet for material (13) is formed in a block (15) housed in a cavity of the body (12) and fixed to the latter by screws (16). The body (12) is provided with a cylindrical cavity (18) obturated by a lateral cover (19) fixed to the body (12) by screws (20). The cavity (18) contains a pusher composed of a first part (21) associated with driving means (22) and of a second part (23) associated with a return spring (24). The valve comprises a slide valve (33) comprising an upper surface (34), a plane lower surface (35) and a traversing conduit (36) formed between the upper surface (34) and the lower surface (35). This slide valve (33) is displaced in a sliding manner on a plate (37) provided with two traversing ducts (38) which communicate with the outlet (14) for the metered material.