Freeze prevention in jet aircraft purge gas generators

Claim 1

A PURGE GAS GENERATING SYSTEM ADAPTED FOR USE IN AN AIRCRAFT WHICH HAS A SOURCE OF AIR UNDER PRESSURE, A RAM AND A DUCT LEADING THEREFROM SERVING AS A SOURCE OF COOLING AIR, AND DUCT WORK LEADING TO SPECES TO BE PURGED, THE COMBINATION COMPRISING: MEANS FORMING A CONDUIT HAVING AN INLET ADAPTED FOR CONNECTION TO SAID SOURCE OF AIR UNDER PRESSURE, SAID CONDUIT HAVING AN OUTLET CONNECTION; SEALED COMBUSTION CHAMBER MEANS HAVING AN AIR INLET, A FUEL INLET AND AN OUTLET FOR PRODUCTS OF COMBUSTION, SAID COMBUSTION CHAMBER AIR INLET BEING CONNECTED TO SAID CONDUIT OUTLET CONNECTION, MEANS FOR SUPPLYING FUEL TO SAID FUEL INLET, MEANS FORMING A HEAT EXCHANGER HAVING A PLURALITY OF GAS PASSES THEREIN CONNECTED IN SERIES, MEANS CONNECTING ONE END OF SAID SERIES TO SAID COMBUSTION CHAMBER OUTLET, MEANS ADAPTED FOR CONNECTING THE OTHER END OF SAID SERIES TO SAID DUCT WORK LEADING TO SPACES TO BE PURGED, MEANS FORMING AN AIR PASSAGE THROUGH SAID HEAT EXCHANGER SUCH THAT AIR IN SAID PASSAGE IS IN HEAT EXCHANGE RELATION TO SAID PASSES, MEANS FOR CONNECTING ONE END OF SAID AIR PASSAGE TO SAID COOLING AIR DUCT, BYPASS MEANS CONNECTED BETWEEN ONE END OF SAID SERIES AND AN INTERMEDIATE PORTION THEREOF FOR SHORT-CIRCUITING SOME OF SAID PASSES, VALVE MEANS IN SAID BYPASS FOR OPENING AND CLOSING THE SAME, MEANS SENSITIVE TO THE TEMPERATURE OF THE PRODUCTS OF COMBUSTION DOWNSTREAM OF SAID PASSES FOR OPENING AND CLOSING SAID VALVE AS THE TEMPERATURE OF SAID TEMPERATURE SENSITIVE MEANS RESPECTIVELY FALLS BELOW AND RISES ABOVE APPROXIMATELY 45* F.