Back-flow preventing valve

Claim 1

IN A FLUID-CONVEYING CONDUIT FORMING AN ENCLOSED OPEN-ENDED PASSAGEWAY, BACK-FLOW PREVENTING MEANS COMPRISING: A FIRST PASSAGEWAY SECTION HAVING AN OUTLET END JOINING THE INLET END OF A SECOND SMALLER PASSAGEWAY SECTION AND WHICH IS SUBSTANTIALLY ALIGNED WITH THE LONGITUDINAL AXIS OF THE SECOND PASSAGEWAY SECTION, THE DEFINING WALL PORTION OF THE INLET END OF SAID SECOND PASSAGEWAY SECTION FORMING AN EXTERNALLY REARWARDLY TAPERED VALVE SEAT PROJECTING INTO SAID FIRST PASSAGEWAY SECTION, VENT OPENING IN SAID CONDUIT OPENING ONTO THE OUTER PORTION OF SAID FIRST PASSAGEWAY SECTION, SAID VENT OPENINGS NORMALLY VENTING THE CONDUIT PASSAGEWAY TO ATMOSPHERIC PRESSURE, AND A RESILIENT DISTENDABLE VALVE MEMBER HAVING A CENTRAL PORTION WITH A GENERALLY PERMANENTLY CYLINDRICAL VALVE PASSAGE THEREIN FOR FLOW OF FLUID THERETHROUGH, SAID VALVE PASSAGE HAVING A DIAMETER WHICH, IN THE UNDISTENDED POSITION OF THE VALVE MEMBER, IS INTERMEDIATE THE LARGEST AND SMALLEST OUTER DIMENSIONS OF SAID REARWARDLY TAPERED VALVE SEAT, SAID VALVE MEMBER BEING DESIGNED TO HAVE A RIGIDITY WHEREIN THE DIAMETER OF SAID VALVE PASSAGE REMAINS INTERMEDIATE THE LARGEST AND SMALLEST OUTER DIMENSIONS OF SAID VALVE SEAT UNDER A PRE-DETERMINED FORWARD FLUID PRESSURE WHICH MOVES THE SAME AGAINST SAID VALVE SEAT, WHEREIN SAID TAPERED VALVE SEAT FITS SNUGLY WITHIN SAID VALVE MEMBER OPENING WHEN THE CENTRAL PORTION OF THE VALVE MEMBER MOVES UNDER FORWARD PRESSURE TO A DOWNSTREAM POSITION, SAID VALVE MEMBER BEING POSITIONED IN THE CONDUIT PASSAGE PASSAGEWAY AT A POINT UPSTREAM FROM BUT CONTIGUOUS TO SAID VENT OPENINGS AND SAID SECOND PASSAGEWAY SECTION, SAID CENTRAL PORTION BEING BODILY MOVABLE UNDER SAID PRE-DETERMINED FORWARD FLUID PRESSURE TO SAID DOWNSTREAM POSITION WHERE SAID CENTRAL PORTION THEREOF SEALS AROUND SAID TAPERED VALVE SEAT TO SEAL OFF THE CONDUIT PASSAGEWAY FROM SAID VENT OPENINGS, AND UNDER ZERO OR BACK PRESSURE TO AN UPSTREAM SUBSTANTIALLY UNDISTENDED POSITION TO UNCOVER THE VENT OPENINGS.