Abstract: The injecting head comprises any number of needle rows, being every one of these needles connected through its top to a plunger arranged inside a fixed cylinder, integral with the head frame, being connected both ends of this cylinder to the liquid injection circuit at a constant pressure from 7 to 8 kg/sq.cm., acting the cylinder as a hydraulic accumulator that allows the coming back of the needles when they strike on an obstacle, being provided a connection through a calibrated controlling device between the two pipes which are supplying the cylinder in order to avoid over-pressures and being also intercalated in the circuit a hydraulic means which assures the keeping of an effective pressure in the top end of that cylinder. The machine includes two filtering tanks, alternately used, and a grease decantation system.