Oxygen breathing device and method for maintaining an emergency oxygen system

1. An emergency oxygen system for use in an aircraft, the emergency oxygen system comprising:

(a) an oxygen source, wherein the oxygen source is a chemical oxygen generator or an oxygen pressure tank,

(b) at least one oxygen mask connected via an oxygen supply line to said oxygen source,

(c) a flow control unit adapted to receive a signal indicating ambient pressure or to detect ambient pressure and to control a flow of oxygen through the oxygen supply line depending on said ambient pressure, wherein the flow control unit is adapted to:

provide a low oxygen flow at a first ambient pressure, and

provide a higher oxygen flow at a second ambient pressure which is lower than said first ambient pressure, and

(d) at least one bypass valve arranged in the oxygen supply line and comprising a first flow path and a second flow path comprising a bypass channel in a parallel flow arrangement to said first flow path, wherein each of said at least one bypass valves is adapted to:

direct the flow of oxygen through said first flow path at an ambient pressure above a predetermined level according to a first flow condition,

direct the flow of oxygen through said second flow path at an ambient pressure below a predetermined level according to a second flow condition, and

wherein said first flow path has a smaller flow cross section than said second flow path, and

wherein the oxygen source, the flow control unit, and the at least one bypass valve are in a serial flow arrangement along the oxygen supply line.

2. The emergency oxygen system according to claim 1 , wherein said first flow path comprises a calibrated orifice.

3. The emergency oxygen system according to claim 1 , wherein said first flow path consists of a flow through a calibrated orifice only and said second flow path consists of a flow through said bypass channel only or through both said bypass channel and said calibrated orifice.

4. The emergency oxygen system according to claim 1 , wherein

each of said at least one bypass valves comprises a first flow channel comprising an orifice with a predetermined cross-section and a second flow channel, wherein a spring biased valve member engages a valve seat and a pressure inside the oxygen supply line acting against said spring biased valve member to switch the spring biased valve member to switch each of the at least one bypass valves between said first and second flow condition.

5. The emergency oxygen system according to claim 1 , wherein:

a plurality of oxygen masks are connected to said oxygen source via a manifold,

the oxygen supply line comprises a first central oxygen line section directing oxygen from the oxygen source to said manifold and a plurality of second oxygen line sections each directing oxygen from the manifold to an oxygen mask, and

each of said at least one bypass valves is arranged in a flow direction between said flow control unit and said oxygen masks.

6. The emergency oxygen system according to claim 1 , wherein:

each of said at least one bypass valves is arranged in a first central oxygen line section in a flow direction between said flow control unit and said manifold.

7. The emergency oxygen system according to claim 5 , wherein the at least one bypass valve comprises a plurality of bypass valves, wherein at least a number of said plurality of second oxygen line sections comprises one of said plurality of bypass valves.

8. The emergency oxygen system according to claim 1 , wherein

each of said at least one bypass valves comprises a first and a second calibrated orifice, said second calibrated orifice having a larger flow cross section than said first calibrated orifice, and wherein:

in said first flow condition the flow of oxygen is flowing through said first calibrated orifice; and

in said second flow condition the flow of oxygen is at least partially circumventing said first calibrated orifice and is flowing through said second calibrated orifice.

9. The emergency oxygen system according to claim 8 , wherein

in said second flow condition a first part of the flow of oxygen is flowing through said first calibrated orifice and a second part of the flow of oxygen is flowing through a bypass line arranged in parallel to said first calibrated orifice.

10. The emergency oxygen system according to claim 8 , wherein

in said first flow condition the flow of oxygen is flowing through said first and second calibrated orifices in a serial arrangement.

11. The emergency oxygen system according to claim 1 , wherein each of said at least one bypass valves comprises:

a housing having an inlet opening and an outlet opening,

a first flow channel connecting said inlet opening and said outlet opening,

a second flow channel connecting said inlet opening and said outlet opening,

a valve piston sealing against a valve seat inside said housing,

wherein, when said valve piston is in sealing contact to said valve seat, the second flow channel is interrupted thus requiring oxygen flowing through each of the at least one bypass valve from the inlet to the outlet opening to flow through said first flow channel, and

wherein, when said valve piston is in a distance position without contact to said valve seat, the second flow channel is open thus allowing oxygen flowing through each of the at least one bypass valves from the inlet to the outlet opening to flow through said first and said second flow channel.

12. The emergency oxygen system according to claim 11 , wherein:

a first calibrated orifice is arranged in the first flow channel, and

a second calibrated orifice is arranged in the second flow channel,

wherein said first calibrated orifice has a smaller flow cross section than said second calibrated orifice.

13. The emergency oxygen system according to claim 11 , wherein:

said piston is hollow,

the first and second flow channel extend through said piston and

said second calibrated orifice is arranged in the piston.

14. A method for providing oxygen to a passenger of an aircraft, comprising the steps of:

providing oxygen from an oxygen source to at least one oxygen mask,

automatically controlling a flow of the oxygen by a flow control unit by:

(a) receiving a signal indicating ambient pressure or detecting ambient pressure; and

(b) controlling the flow of the oxygen through an oxygen supply line depending on said ambient pressure, in that a low oxygen flow is provided at a first ambient pressure, and a higher oxygen flow is provided at a second ambient pressure which is lower than said first ambient pressure, and

directing the oxygen from said flow control unit to said oxygen mask via a bypass valve arranged in a serial flow arrangement along the oxygen supply line with the flow control unit, the bypass valve comprising a first flow path and a second flow path comprising a bypass channel in a parallel flow arrangement to said first flow path, wherein said first flow path has a smaller cross section than said second flow path and wherein said bypass valve:

(a) directs the flow of the oxygen through said first flow path at an ambient pressure above a predetermined level according to a first flow condition, and

(b) directs the flow of the oxygen through said second flow path at an ambient pressure below a predetermined level according to a second flow condition.

15. A method for maintaining an emergency oxygen system of an aircraft, said emergency oxygen system comprising:

installing an oxygen source comprising a chemical oxygen generator or an oxygen pressure tank,

installing at least one oxygen mask connected via an oxygen supply line to said oxygen source,

installing a flow control unit in a serial flow arrangement with said oxygen source along the oxygen supply line, wherein said flow control unit is adapted to receive a signal indicating ambient pressure or to detect ambient pressure and to control a flow of oxygen through the oxygen supply line depending on said ambient pressure, wherein the flow control unit is adapted to:

(a) provide a low oxygen flow at a first ambient pressure,

(b) provide a higher oxygen flow at a second ambient pressure which is lower than said first ambient pressure, and

(c) to increase said flow of oxygen in at least two steps, and

installing a bypass valve in a serial arrangement with said flow control unit along the oxygen supply line, said bypass valve comprising a first flow path and a second flow path comprising a bypass channel in a parallel flow arrangement to said first flow path, wherein said bypass valve is adapted to:

(a) direct the flow of oxygen through said first flow path at an ambient pressure above a predetermined level according to a first flow condition, and

(b) direct the flow of oxygen through said second flow path at an ambient pressure below a predetermined level according to a second flow condition,

(c) wherein said first flow path has a smaller flow cross section than said second flow path.

16. The emergency oxygen system of claim 1 , wherein the at least one oxygen mask comprises a plurality of oxygen masks and wherein the emergency oxygen system further comprises a first manifold that distributes the flow of oxygen from the at least one bypass valve to a plurality of second manifolds, and

wherein each of the plurality of second manifolds distributes the flow of oxygen from the first manifold to a subset of the plurality of oxygen masks,

wherein the oxygen supply line comprises a plurality of individual oxygen supply line sections, and

wherein each of the individual oxygen supply line sections connects one of the oxygen masks of the subset of the plurality of oxygen masks with one of the plurality of second manifolds and wherein each of the individual oxygen supply line sections comprises a restrictor.

17. The emergency oxygen system of claim 1 , wherein the at least one oxygen mask comprises a plurality of oxygen masks, wherein the at least one bypass valve comprises a plurality of bypass valves and wherein the emergency oxygen system further comprises:

a first manifold that distributes the flow of oxygen from the flow control unit to the plurality of bypass valves;

a plurality of second manifolds, wherein each of the plurality of second manifolds distributes the flow of oxygen from one of the plurality of bypass valves to a subset of the plurality of oxygen masks;

wherein the oxygen supply line comprises a plurality of individual oxygen supply line sections; and

wherein each of the individual oxygen supply line sections connects one of the oxygen masks of the subset of the plurality of oxygen masks with one of the plurality of second manifolds and wherein each of the individual oxygen supply line sections comprises a restrictor.

18. The emergency oxygen system of claim 1 , wherein the at least one oxygen mask comprises a plurality of oxygen masks, wherein the at least one bypass valve comprises a plurality of bypass valves and wherein the emergency oxygen system further comprises:

a first manifold that distributes the flow of oxygen from the flow control unit to a plurality of second manifolds;

wherein each of the plurality of second manifolds distributes the flow of oxygen from the first manifold to a subset of the plurality of bypass valves;

wherein each of the bypass valves of the subset of the plurality of bypass valves delivers the flow of oxygen to one of the plurality of oxygen masks via an individual oxygen supply line section of the oxygen supply line; and

wherein a restrictor is integrated into each of the plurality of bypass valves.