Stepped-opening diaphragm gas valve

Claim 1

IN A DIAPHRAGM GAS VALVE, MAIN VALVE BODY HAVING A FIRST CHAMBER FORMED THEREIN, A MAIN FUEL INLET PASSAGEWAY LEADING TO SAID FIRST CHAMBER, A MAIN FUEL OUTLET PASSAGEWAY LEADING FROM SAID FIRST CHAMBER, AND A MAIN VALVE CONTROLLING SAID OUTLET PASSAGEWAY, A COVER MEMBER FOR SAID VALVE BODY, A SECOND CHAMBER, FORMED IN SAID COVERMEMBER, A FLEXIBLE DIAPHRAGM FORMING A DIVIDING WALL BETWEEN SAID FIRST AND SECOND CHAMBERS AND BEING OPERATIVELY CONNECTED TO SAID MAIN VALVE, MEANS BIASING SAID VALVE IN A CLOSED POSITION, MEANS FORMING A FIRST COMMUNICATING PASSAGEWAY CONNECTING SAID FIRST AND SECOND CHAMBERS, AND MEANS FORMING A SECOND COMMUNICATING PASSAGEWAY LEADING FROM SAID SECOND CHAMBER TO ATMOSPHERE, A TWOPOSITION PILOT VALVE OPERATIVE TO ALTERNATELY CLOSE AND OPEN EACH OF SAID COMMUNICATING PASSAGEWAYS AS IT IS MOVED BACK AND FORTH FROM ITS ONE POSITION TO THE OTHER, MEANS FORMING A BRANCH OF SAID SECOND COMMUNICATING PASSAGEWAY LEADING FROM A POINT IN SAID SECOND COMMUNICATING PASSAGEWAY BETWEEN SAID PILOT VALVE AND ATMOSPHERE TO A POINT IN SAID MAIN FUEL OUTLET PASSAGEWAY DOWNSTREAM FROM SAID MAIN VALVE, AND A NORMALLY CLOSED CHECK VALVE IN SAID BRANCH COMMUNICATING PASSAGEWAY ARRANGED TO OPEN WHEN THE PRESSURE IN SAID BRANCH COMMUNICATING PASSAGEWAY IS GREATER THAN THAT IN SAID MAIN FUEL OUTLET PASSAGEWAY.