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A method of controlling a gas adsorption apparatus including a sieve bed containing molecular sieve bed material, the bed being cyclically operable in a charge mode to adsorb non-product gas from an air supply thereby to increase the concentration of a product gas in a product gas supply which passe

A method of controlling a gas adsorption apparatus including a sieve bed containing molecular sieve bed material, the bed being cyclically operable in a charge mode to adsorb non-product gas from an air supply thereby to increase the concentration of a product gas in a product gas supply which passes to a product gas line and in a vent mode to desorb the adsorbed non-product gas which passes to a non-product gas line, and there being a passage to permit a restricted amount only of the product gas supply to pass from the product gas supply line to the bed when operating in vent mode, and wherein the method includes operating a variable flow device to permit an increased amount of the product gas supply to pass to the bed when operating in vent mode, under predetermined conditions.

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The invention claimed is: 1. A method of controlling a gas adsorption apparatus for producing a breathable product gas supply for a main supply system in an aircraft including at least one sieve bed containing molecular sieve bed material, the sieve bed being cyclically operable in a charge mode to

The invention claimed is: 1. A method of controlling a gas adsorption apparatus for producing a breathable product gas supply for a main supply system in an aircraft including at least one sieve bed containing molecular sieve bed material, the sieve bed being cyclically operable in a charge mode to adsorb non-product gas from an air supply thereby to increase the concentration of a product gas in a product gas supply line which passes to a product gas supply, and in a vent mode to desorb the adsorbed non-product gas which passes to a non-product gas line, and there being at least one passage to permit a restricted amount only of the product gas supply to pass from the product gas supply line to the bed when operating in the vent mode, and wherein the method includes operating a variable flow device to permit an increased amount of the product gas supply to pass to the bed when operating in the vent mode, under predetermined conditions, wherein at above a threshold altitude a minimum amount of the product gas supply is permitted to flow into the bed when operating in the vent mode, and further including the step of automatically operating the variable flow device in response to an altitude sensor input, to increase or reduce the amount of product gas supply passing to the venting bed at the threshold altitude, depending upon whether the aircraft is climbing or descending. 2. A method according to claim 1 wherein said at least one gas adsorption apparatus comprises at least two sieve beds each containing molecular sieve bed material, each sieve bed being cyclically operable in charge mode and in vent mode, and wherein the beds are operated so at least for some of the time when each of the beds is operating in charge mode, the other or another of the beds is operating in vent mode. 3. A method according to claim 2 wherein product gas supply from each bed, when operating in charge mode, passes to its own individual product gas supply line, which lines are connected downstream of a non-return valve, to a main supply system, the non-return valves preventing product gas passing from the main supply system to each respective sieve bed. 4. A method according to claim 3 wherein first and second passages are provided to extend between the product gas supply lines from the beds upstream of the non-return valves. 5. A method according to claim 1, wherein two parallel passages are provided to permit a restricted amount only of the product gas supply to pass from the product gas supply line to the bed when operating in the vent mode, wherein a first of the parallel passages is provided with a flow restrictor which permits a restricted amount of the product gas supply to pass to the bed or beds at all times, and the variable flow device is provided in a second of the parallel passages. 6. A method according to claim 1 wherein the variable flow device is provided in the at least one passage and is operable under all conditions to permit at least the restricted amount of the product gas supply to pass from the product gas supply line to the bed when operating in vent mode, and to permit the increased flow under the predetermined conditions. 7. A method according to claim 1 wherein the variable flow device is a simple shut-off valve, in combination with or otherwise containing a flow restrictor which restricts the gas flow through to a maximum amount of the product gas supply when the shut-off valve is opened. 8. A method according to claim 1 wherein the variable flow device is operable to permit infinitely or incrementally varying amounts of the product gas supply to flow to the bed or beds. 9. A method of controlling a gas adsorption apparatus for producing a breathable product gas supply in an aircraft including at least one sieve bed containing molecular sieve bed material, the sieve bed being cyclically operable in a charge mode to adsorb non-product gas from an air supply thereby to increase the concentration of a product gas in a product gas supply line which passes to a product gas supply, and in a vent mode to desorb the adsorbed non-product gas which passes to a non-product gas line, and there being a passage to permit a restricted amount only of the product gas supply to pass from the product gas supply line to the bed when operating in vent mode, and wherein the method includes operating a variable flow device to permit an infinitely or an incrementally varying increased amount of the product gas supply to pass to the bed when operating in vent mode, under predetermined conditions, wherein at above a threshold altitude a minimum amount of the product gas supply is permitted to flow into the bed when operating in vent mode and wherein as the aircraft climbs and descends, the variable flow device is operated to permit an infinitely varying amount of product gas supply to flow to the bed or beds to match product gas supply demand to altitude. 10. A method according to claim 8 wherein the gas adsorption apparatus is for producing a breathable product gas supply in an aircraft, and at above a threshold altitude a minimum amount of the product gas supply is permitted to flow into the bed when operating in vent mode and wherein the method includes sensing the concentration of product gas in the product gas supply available for breathing, sensing the aircraft altitude, and adjusting the variable flow device to ensure that a concentration of product gas in the product gas supply is available for breathing. 11. A gas adsorption apparatus for use in an aircraft including at least one sieve bed containing molecular sieve bed material, flow control valves connected to alternately operate each bed in a charge mode to adsorb non-product gas from an air supply thereby to increase the concentration of a product gas in a product gas supply which passes to a product gas line, and in a vent mode to desorb the adsorbed non-product gas which passes to a non-product gas line, and there being a passage to permit a restricted amount only of the product gas supply to pass from the product gas supply line to the bed when operating in vent mode, and characterized in that the apparatus includes a variable flow device which is operable to permit an increased amount of the product gas supply to pass to the bed when operating in vent mode, under predetermined conditions, and wherein the variable flow device is operatively connected to an altitude sensor. 12. An apparatus according to claim 11 wherein said at least one molecular sieve bed comprises at least two sieve beds each containing molecular sieve bed material, each bed being cyclically operable in the charge mode and in the vent mode, the beds being operated so at least for some of the time when each of the beds is operating in the charge mode, the other or another of the beds is operating in the vent mode, the apparatus including for each sieve bed, an inlet valve and an outlet valve, each inlet valve being open when its respective bed is operated in charge mode, to allow air from the air supply to flow into the respective sieve bed, and each outlet valve being open when its respective bed is operated in the vent mode, to allow desorbed non-product gas to flow from the respective sieve bed. 13. An apparatus according to claim 12 wherein the inlet and outlet valves are controlled by control valves in response to a system controller. 14. An apparatus according to claim 13 wherein the inlet and outlet valves are each diaphragm valves to which pressurized air is selectively fed to close the valves from powered control valves when de-energized.