1. IN APPARATUS FOR STORING GRANULAR MATERIAL INCLUDING STRUCTURE DEFINING A STORAGE HOPPER PROVIDED WITH A BOTTOM DISCHARGE OUTLET; AN OUTLET NOZZLE COMPRISING A CASING CARRIED BY SAID STORAGE HOPPER AND DISPOSED BELOW SAID BOTTOM OUTLET AND COMMUNICATING THEREWITH, A SUCTION TUBE EXTENDING THROUGH THE LOWER PORTION OF SAID CASING FOR UNLOADING THE GRANULAR MATERIAL FROM SAID STORAGE HOPPER THROUGH SAID CASING, ONE END OF SAID TUBE PROVIDING AN AIR INLET OPENING THEREINTO AND THE OTHER END OF SAID TUBE PROVIDING AN AIR OUTLET OPENING THEREFROM, THE INTERMEDIATE SECTION OF SAID TUBE BEING DISPOSED WITHIN SAID CASING AND HAVING A VALVE PORT PROVIDED IN THE BOTTOM THEREOF, A VALVE ELEMENT ARRANGED IN THE LOWER PORTION OF SAID CASING BELOW SAID VALVE PORT AND COOPERATING THEREWITH, WHEREBY THE INTERIOR OF SAID TUBE IS IN COMMUNICATION WITH THE LOWER PORTION OF SAID CASING WHEN SAOD VALVE ELEMENT OCCUPIES ITS OPEN POSITION WITH RESPECT TO SAID VALVE PORT AND THE INTERIOR OF SAID TUBE IS CUTOFF FROM COMMUNICATION WITH THE LOWER PORTION OF SAID CASING WHEN SAID VALVE ELEMENT OCCUPIES ITS CLOSED POSITION WITH RESPECT TO SAID VALVE PORT, A FIXTURE COMMUNICATING WITH SAID OTHER END OF SAID TUBE AND ADAPTED TO BE CONNECTED TO A SUCTION CONDUIT, WHEREBY CONVEYING AIR MAY BE SUPPLIED THROUGH SAID AIR INLET OPENING INTO SAID TUBE AND THEN THROUGH SAID AIR OUTLET OPENING INTO THE SUCTION CONDUIT CONNECTED TO SAID FIXTURE WITH THE RESULT THAT THE GRANULAR MATERIAL IN SAID STORAGE HOPPER IS UNLOADED THEREFROM INTO SAID CASING AND PROCEEDS THEREFROM THROUGH SAID VALVE PORT WITH SAID VALVE ELEMENT IN ITS OPEN POSITION AND INTO SAID TUBE AND IS THUS CONVEYED WITH THE CONVEYING AIR IN SAID TUBE INTO THE SUCTION CONDUIT CONNECTED TO SAID FIXTURE, AND MECHANISM FOR SELECTIVELY ACTUATING SAID VALVE ELEMENT BETWEEN ITS OPEN AND CLOSED POSITIONS WITH RESPECT TO SAID VALVE PORT; SAID MECHANISM COMPRISING A DAIPHRAGM ARRANGED IN THE LOWER PORTION OF SAID CASING IN SUPPORTING AND SURROUNDING RELATION WITH SAID VALVE ELEMENT, THE INNER PERIMETER OF SAID DIAPHRAG BEING SEALED TO SID VALVE ELEMENT AND THE OUTER PERIMETER OF SAID DIAPHRAGM BEING SEALED TO SAID CASING THEREBY TO DEFINE A CHAMBER BELOW SAID VALVE ELEMENT AND SAID DAIPHRAGM AND ABOVE THE BOTTOM OF SAID CASING, SAID DIAPHRAGM HAVING A LOWER POSITION ACTUATING SAID VALVE ELEMENT INTO ITS OPEN POSITION WITH RESPECT TO SAID VALVE PORT AND AN UPPER POSITION ACTUATING SAID VALVE ELEMENT INTO ITS CLOSED POSITION WITH RESPECT TO SAID VALVE PORT, THE UPPER SIDE OF SAID VALVE ELEMENT AND THE UPPER SIDE OF SAID DIAPHRAGM BEING SUBJECT TO THE AIR PRESSURE IN THE LOWER PORTION OF SAID CASING AND THE LOWER SIDE OF SAID VALVE ELEMENT AND THE LOWER SIDE OF SAID DAIPHRAGM BEING SUBJECT TO THE AIR PRESSURE IN SAID CHAMBER, THE UPPER SIDE OF SAID VALVE ELEMENT AND THE UPPER SIDE OF SAID DIAPHRAGM ALSO BEING SUBJECT TO THE WEIGHT OF GRANULAR MATERIAL IN THE LOWER PORTION OF SAID CASING SO LONG AS THERE IS GRANULAR MATERIAL IN SAID STORAGE HOPPER TO BE UNLOADED THEREFROM, AND MEANS DEFINING A RESTRICTED PASSAGE BETWEEN THE LOWER PORTION OF SAID CASING AND SAID CHAMBER, THE OPENING INTO SAID PASSAGE IN THE LOWER PORTION OF SAID CASING BEING LOCATED WELL OUTWARDLY FROM SAID VALVE PORT AND SAID VALVE ELEMENT, WHEREBY THE ABSENCE OF SUCTION IN THE TUBE CONCURRENTLY WITH OR WITHOUT GRANULAR MATERIAL IN THE LOWER PORTION OF SAID CASING SUBJECTS THE UPPER SIDE OF SAID VALVE ELEMENT AND THE UPPER SIDE OF SAID DIAPHRAGM AND SAID OPENING INTO SAID PASSAGE TO RELATIVELY HIGH AIR PRESSURE SO THAT SAID CHAMBER IS SUBJECT TO RELATIVELY HIGH AIR PRESSURE WITH THE RESULT THAT SAID DIAPHRAGM IS OPERATED INTO ITS LOWER POSITION, AND WHEREBY SUCTION IN SAID TUBE CONCURRENTLY WITH THE PRESENCE OF GRANULAR MATERIAL IN THE LOWER PORTION OF SAID CASING SUBJECTS THE UPPER SIDE OF SAID VALVE ELEMENT AND THE UPPER SIDE OF SAID DIAPHRAGM AND SAID OPENING INTO SAID PASSAGE TO RELATIVELY LOW AIR PRESSURE SO THAT SAID CHAMBER IS SUBJECT TO RELATIVELY LOW AIR PRESSURE WITH THE RESULT THAT SAID DAIPHRAGM IS OPERATED INTO ITS LOWER POSITION, AND WHEREBY SUCTION IN SAID TUBE CONCURRENTLY WITH THE ABSENCE OF GRANULAR MATERIAL IN THE LOWER PORTION OF SAID CASING SUBJECTS THE UPPER SIDE OF SAID VALVE ELEMENT TO RELATIVELY LOW AIR PRESSURE AND SUBJECTS THE UPPER SIDE OF SAID DIAPHRAGM AND SAID OPENING INTO SAID PASSAGE TO RELATIVELY HIGH AIR PRESSURE SO THAT SAID CHAMBER IS SUBJECT TO RELATIVELY HIGH AIR PRESSURE WITH THE RESULT THAT SAID DIAPHRAGM IS OPERATED INTO ITS UPPER POSITION.