Compensated action non-return valve, more particularly for respiratory mask

Claim 1

AN AUTOMATICALLY ADJUSTED NON-RETURN VALVE HAVING A DELIVERY END AND SUPPLIED FROM A SUPPLY LINE, THE IMPROVEMENT COMPRISING AN OPENED AND PERFORATED CASING FOR SAID VALVE, A PERFORATED COVER FIXEDLY CONNECTED TO SAID CASING ON THE OPENING THEREOF, SAID PERFORATED COVER HAVING ITS PERFORATION OPENING AT THE DELIVERY END OF SAID VALVE, AN ANNULAR SEATING INTEGRAL WITH SAID COVER AND EXTENDING TOWARD THE INSIDE OF THE CASING AN AXIALLY DISTORTABLE THIN WALLED BELLOWS CONNECTED AT ITS LOWER PORTION OF SAID CASING AT THE BOTTOM THEROF, A PERFORATED PLATE CONNECTED TO SAID BELLOWS AT ITS UPPER PART AND PARTIALLY OVERLAPPED BY AN UPPER ANNULAR PORTION OF SAID BELLOWS, SAID OVERLAPPING PORTION DEFINING AN OPENING IN SAID UPPER PART OF SAID BELLOWS AND CONSTITUTING A FLEXIBLE LINING TO COOPERATE WITH SAID ANNULAR SEATING THE DIAMETER OF WHICH IS SLIGHTLY SMALLER THAN THE DIAMETER OF SAID PERFORATED PLATE, A FLEXIBLE SEATING EXTENDING TOWARD SAID COVER AND LYING AT THE INNER PERIPHERY OF SAID UPPER OVERLAPPING PORTION OF THE BELLOWS, MEANS PREVENTING RADIAL DEFORMATION OF SAID BELLOWS, A STEM FLAT-VALVE MOUNTED TO BEAR ONTO SAID FLEXIBLE SEATING THUS CLOSING THE UPPER PORTION OF THE BELLOWS, TWO GUIDING SLEEVES RESPECTIVELY CARRIED BY SAID PERFORATED PLATE AND BY SAID CASING TO GUIDE SAID STEM OF SAID STEM FLAT-VALVE, AN ABUTTING MEMBER MOUNTED ON SAID STEM, A LOADED SPRING INTERPOSED BETWEEN SAID ABUTTING MEMBER AND SAID PERFORATED PLATE,