Non-return device for continuous presses, partic. those used for the treatment of grapes, is associated with an Archimedean screw rotating in a feed hopper and a cylindrical channel; at least one blade of the screw is reversed with respect to the remainder. The press comprises a feed hopper, a cylindrical channel, the screw driven by the motor and a flap valve with a hydraulic jack regulator. The screw is in two portions so that one part is in the hopper and the remainder in the channel. The non-return device is between the two portions and consists of two blades with a reversed thread, mounted by means of flanges on the portions (3a, 3b) of the cylindrical channel. The part of the screw is prolonged by a shaft passing through the device; the part is keyed to this shaft and kept in position by a nut screwed to its end. The normal progression of the material in the press is practically unrestricted and a notable economy in energy is achieved.
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