Volume cycled medical ventilators

Claim 1

A VOLUME CYCLED RESPIRATOR COMPRISING A BELLOWS OPERATIVELY CONNECTED WITH A LEVER, AN INLET PORT CONNECTING THE INTERIOR OF THE BELLOWS WITH A CONTINUOUS PRESSURE GAS SUPPLY, AN OUTLET DUCT FOR SAID BELLOWS COMMUNICATING WITH A VALVE CHAMBER, IN SAID CHAMBER A VALVE WHICH IN A FIRST POSITION BLOCKS AN OUTLET DUCT FROM A PATIENT WHILE PERMITTING THE PASSAGE OF PRESSURE GAS THROUGH THE CHAMBER TO AN INLET DUCT TO THE PATIENT, WHEREAS IN A SECOND AND ALTERNATIVE POSITION SAID VALVE PERMITS THE SAID OUTLET DUCT TO HAVE FREE ACCESS TO ATMOSPHERE WHILE BLOCKING THE PASSAGE OF GAS THROUGH THE CHAMBER TO THE INLET DUCT, A VALVE CONTROLLING MECHANISM WHICH AT THE END OF THE INSPIRATORY PERIOD IS OPERATED BY SAID LEVER TO MOVE THE SAID VALVE FROM SAID FIRST POSITION TO SAID SECOND POSITION AND COMPRISING MEANS WHICH, ON THE VOLUME OF GAS IN SAID BELLOWS HAVING REACHED A PREDETERMINED UPPER MAGNITUDE, CAUSE SAID LEVER TO OPERATE THE VALVE CONTROL MECHANISM TO RETURN THE VALVE TO THE FIRST SAID POSITION AND COMPRISING SPRING MEANS ADAPTED TO URGE SAID VALVE TOWARDS THE SECOND POSITION AND A MAGNETIC CIRCUIT INCLUDING A PORTION MOVABLE WITH SAID VALVE AND ADAPTED TO HOLD SAID VALVE IN THE FIRST POSITION AGAINST THE PRESSURE OF SAID SPRING MEANS WHEN THE SPRING PRESSURE IS LESS THAN A PREDETERMINED MAGNITUDE, AND MEANS ASSOCIATED WITH THE CONTRACTION OF THE BELLOWS OF SAID VENTILATOR, MECHANICALLY TO INCREASE SAID SPRING PRESSURE TO A MAGNITUDE GREATER THAN SAID PREDETERMINED MAGNITUDE WHEREUPON SAID SPRING BREAKS THE MAGNETIC CIRCUIT AND URGES SAID VALVE TO THE SECOND POSITION.