a blow molding system for a thermoplastic blank which is supported in a mold . the system includes a fixed tubular body connected to a high - pressure fluid source and , at the lower end thereof , supporting moveable equipment consisting of a tuyere , the tuyere being defined laterally by a terminal sleeve of the moveable equipment and the bottom thereof being the front wall of the body , wherein the lateral inner wall of the sleeve is configured in such a way that the pressure of a fluid inside the tuyere does not result in a reaction force component on the lateral wall , which is directed opposite to the wall of the mold .