distribution preventing the bursting of solid particles and the imprisonment of juice in solid matter as a result of which lower pressures can be applied than are necessary in the known apparatus if the shield cone 50 is made fairly slender starting from its apex and if the widening of the cone 50 is sharply increased as shown in fig5 a passage section is obtained which decreases progressively and then more abruptly correlatively producing a retaining force increasing slightly and then more sharply in order to achieve effective extraction of the liquid fractions at the end of the cycle the drying of the mixture is thus modulated in accordance with the pressure prevailing in the jack 57 and therefore in accordance with the retaining force of the shield 50 the different functions can obviously be carried out by means of a central automatic control station receiving information from limit stops contactors sensors pressure gauges and the like in order to prevent any return of mixture from the vessel 14 to the tank 2 when the vessel 14 is moved in the direction of the arrows f5 a non return valve may be provided as illustrated in fig9 in this figure the sleeve 11 its front part 13 and its central passage 12 through.