Low liquid level shut-off apparatus for gas burner

Claim 1

IN COMBINATION, A VESSEL OPEN TO THE ATMOSPHERE AND ADAPTED TO CONTAIN A LIQUID TO BE HEATED, A BURNER FOR HEATING THE LIQUID, AND A GAS SUPPLY LINE TO THE BURNER, (A) A VALVE HOUSING IN SAID GAS SUPPLY LINE HAVING A GAS INLET AND A GAS OUTLET AND HAVING A VALVE THEREIN DISPOSED TO MOVE SELECTIVELY FROM A CLOSED, SEATED POSITION TO AN OPEN POSITION, (B) A VALVE STEM CONNECTED TO SAID VALVE, (C) A FIRST DIAPHRAGM CARRIED BY SAID VALVE STEM AND DEFINING A SEAL FOR ONE SIDE OF THE VALVE HOUSING, (D) A SECOND DIAPHRAGM CARRIED BY SAID VALVE STEM AND SPACED FROM SAID FIRST DIAPHRAGM TO DEFINE A CLOSED CHAMBER THEREBETWEEN, (E) THERE BEING A TAP PASSAGEWAY COMMUNICATING SAID CLOSED CHAMBER WITH THE GAS INLET SO THAT THE GAS PRESSURE AT SAID INLET EXERTS A FORCE TO AID IN CLOSSAID VALVE, (F) ADJUSTABLE SPRING MEANS URGING SAID VALVE TOWARD OPEN POSITION, (G) COUNTER SPRING MEANS URGING SAID VALVE TOWARD CLOSED PORTION, (H) A SECOND CLOSED CHAMBER AT THE OPPOSITE SIDE OF SAID SECOND DIAPHRAGM FROM THE FIRST MENTIONED CLOSED CHAMBER, (I) A CONDUIT COMMUNICATING WITH SAID SECOND CLOSED CHAMBER, AND (J) A DEPENDING DIP TUBE HAVING A LOWER OPEN END AND COMMUNICATING AT ITS UPPER END WITH THE LOWER END OF SAID CONDUIT IN POSITION TO EXTEND DOWNWARDLY INTO THE LIQUID IN SAID VESSEL AND TRAP AIT WITHIN SAID DIP TUBE SO THAT PRESSURE IS ENCREASED AND DECREASED WITHIN SAID SECOND CLOSED CHAMBER IN RESPONSE TO A RISE AND FALL, RESPECTIVELY, IN THE LIQUID LEVEL IN SAID VESSEL, WHEREBY ABOVE A PREDETERMINED LIQUID LEVEL IN THE VESSEL PRESSURE WITHIN SAID SECOND CHAMBER OVERCOMES THE PRESSURE OF THE INLET GAS AND THE FORCE EXERTED BY SAID COUNTER SPRING TO OPEN SAID VALVE AND BELOW SAID PREDETERMINED LEVEL IN THE VESSEL PRESSURE IS REDUCED WITHIN SAID SECOND CHAMBER AND THE PRESSURE OF THE INLET GAS AND THE FORCE EXERTED BY SAID COUNTER SPRING CLOSES SAID VALVE.