1. IN APPARATUS FOR STORING GRANULAR MATERIAL, STRUCTURE DEFINING A PLURALITY OF STORAGE HOPPERS RESPECTIVELY PROVIDED WITH A PLURALITY OF BOTTOM DISCHARGE OUTLETS, A PLURALITY OF OUTLET NOZZLES RESPECTIVELY CARRIED BY SAID STORAGE HOPPERS, EACH OF SAID OUTLET NOZZLES INCLUDING A CASING DISPOSED BELOW THE BOTTOM OUTLET IN THE ASSOCIATED ONE OF SAID STORAGE HOPPERS AND COMMUNICATING THEREWITH, EACH OF SAID OUTLET NOZZLES ALSO INCLUDING A SUCTION TUBE EXTENDING THROUGH THE LOWER PORTION OF THE ASSOCATED CASING FOR UNLOADING THE GRANULAR MATERIAL FROM THE ASSOCIATED ONE OF SAID STORAGE HOPPERS, THE INTERMEDIATE SECTION OF EACH OF SAID TUBES BEING DISPOSED WITHIN THE ASSOCIATED CASING AND HAVING A VALVE PORT PROVIDED IN THE BOTTOM THEREOF AND COMMUNICATING WITH THE LOWER PORTION OF THE ASSOCIATED CASING, EACH OF SAID OUTLET NOZZLES FURTHER INCLUDING A VALVE ELEMENT ARRANGED IN THE LOWER PORTION OF THE ASSOCIATED CASING AND DISPOSED BELOW THE VALE PORT IN THE ASSOCIATED TUBE AND COOPERATING THEREWITH, WHEREBY THE INTERIOR OF EACH OF SAID TUBES IS IN COMMUNICATION WITH THE LOWER PORTION OF THE ASSOCIATED CASING WHEN THE ASSOCIATED VALVE ELEMENT OCCUPIES ITS OPEN POSITION WITH RESPECT TO THE ASSOCIATED VALVE PORT AND THE INTERIOR OF EACH OF SAID TUBES IS CUT-OFF FROM COMMUNICATION WITH THE LOWER PORTION OF THE ASSOCIATED CASING WHEN THE ASSOCIATED VALVE ELEMENT OCCUPIES ITS CLOSED POSITION WITH RESPECT TO THE ASSOCIATED VALVE PORT, EACH OF SAID SUCTION NOZZLES FURTHER INCLUDING ACTUATING MEANS FOR SELECTIVELY OPERATING THE ASSOCIATED VALVE ELEMENT BETWEEM ITS OPEN AND CLOSED POSITIONS WITH RESPECT TO THE ASSOCIATED VALVE PORT, EACH OF SAID VALVE ELEMENTS BEING OPERATED BY THE ASSOCIATED ACTUATING MEANS INTO ITS OPEN POSITION WITH RESPECT TO THE ASSOCIATED VALVE PORT IN RESPONSE TO THE PRESENCE OF THE GRANULAR MATERIAL IN THE AS-