1. A PROPORTIONING PUMP FOR GASEOUS FLUID COMPRISING A PUMP BODY, A TRANSVERSE PARTITION DIVIDING SAID BODY INTERNALLY INTO TWO CHAMBERS OF SUBSTANTIALLY IDENTICAL VOLUME, CHARACTERIZED IN THAT A METALLIC BELLOW IS DISPOSED IN EACH OF SAID CHAMBERS, ONE END OF SAID BELLOWS BEING SECURED TO THE PUMP BODY, A MOVABLE PISTON DISPOSED WITHIN SAID CLOSING THE OTHER END OF EACH OF SAID BELLOWS AND BEING RIGIDLY FIXED THERETO, SAID MOVABLE PISTON PROVIDING WITHIN SAID BELLOWS A VOLUME WHICH IS VARIABLE AS A FUNCTION OF THE POSITION OF SAID PISTON INSIDE THE CHAMBER, A RIGID UNIDIRECTIONAL COUPLING CONNECTING THE MOVABLE PISTONS OF THE TWO CHAMBERS TO EACH OTHER THROUGH THE TRANSVERSE PARTITION; MEANS FOR CONNECTING THE INTERIOR OF EACH OF SAID BELLOWS TO A GASEOUS FLUID PROPORTIONING CIRCUIT; AND MEANS FOR CONNECTING EACH OF SAID CHAMBERS TO A FLUID MOTOR CIRCUIT.