Abstract:
A safety device is provided for a gas distribution system in an airplane, containing at least one pressure regulator ( 5 ) between a pressurized gas source ( 2 ) and a supply line. Reliability of operation is improved with the provision of a pressure-limiting device ( 4 ) with two lines ( 41, 42 ) arranged in parallel with two pressure-limiting valves ( 43, 44, 45, 46 ) each arranged in the same direction in series. The pressure-limiting device ( 4 ) is arranged upstream of the pressure regulator ( 5 ).

Description:
FIELD OF THE INVENTION 
     The present invention pertains to a safety device for a gas distribution system in an airplane, containing at least one pressure reducer between a pressurized gas source and a supply line. 
     BACKGROUND OF THE INVENTION 
     A device for supplying the passengers and the crew with oxygen has become known from U.S. Pat. No. 2,934,293. Based on individual pressurized oxygen cylinders, which are connected to one another via a line system, the oxygen is sent into supply lines via pressure-reducing valves. The supply lines extending to the left and right of the rows of passengers are branched off from a distributor and are connected to emergency oxygen supply means, which are located next to the passenger seats. Supply lines for oxygen with separate pressure regulators are additionally provided for the pilots and the crew. 
     Pressure-reducing valves, which are connected to one another via individual pressure relief lines, are provided at the pressurized gas cylinders in the prior-art gas distribution systems, and excess gas is blown off via a common gas outlet to eliminate pressure peaks. A corresponding number of pressure-limiting valves, which must be maintained individually, are also needed in light of a large number of pressurized gas cylinders. Such pressure relief valves are usually connected in one assembly unit to a cylinder pressure reducer located on the pressurized gas cylinder. The housing of the cylinder pressure reducer has a separate outlet connection, via which the gas flowing from the pressure relief valve is drawn off. Such a cylinder pressure reducer is shown, e.g., in EP 298 272 A2. 
     SUMMARY OF THE INVENTION 
     The basic object of the present invention is to improve a safety device of the type described in terms of its reliability of operation. 
     According to the invention, a safety device for a gas distribution system in an airplane is provided containing at least one pressure reducer between a pressurized gas source and a supply line. A pressure-limiting means is arranged upstream of the pressure regulator. The pressure-limiting means has two lines arranged in parallel with two pressure-limiting valves each arranged in the same direction in series. 
     The safety device described in the present invention has the advantage that only a single pressure-limiting means, which is designed as a doubly redundant pressure-limiting means and replaces the individual valves, is needed for a battery of individual pressurized gas cylinders. 
     Two identical pressure-limiting valves are arranged here in lines connected in parallel such that flow is possible through each line in the same direction. The pressure-limiting means is located between the pressurized gas sources and the pressure reducer and is used to limit the admission pressure to the pressure regulator. The pressure-limiting function of the pressure-limiting means is guaranteed by the partially parallel and serial arrangement of the pressure-limiting valves both in case of failure of one of the pressure-limiting valves and in case of failure of a single pressure-limiting valve in each of the lines connected in parallel. The possible cases of error, such as jamming of a pressure-limiting valve in the open or closed position, are thus covered. The pressure regulator, which is provided with the pressure-limiting means, is located with respect to the flow behind the cylinder pressure reducers, which are screwed onto the pressurized gas cylinders, and they reduce the pressure in the cylinder to the so-called center pressure. 
     The pressure-limiting valves are advantageously designed as spring-loaded nonreturn valves opening at a predetermined limit pressure. The nonreturn valves are advantageously designed such that they have the same limit pressure. 
     Two pressure regulators connected in parallel, which operate independently from one another as altitude-controlled differential pressure regulators, are advantageously provided as pressure regulators. The pressure profile rises linearly from 400 mbar to 6,800 mbar in the altitude range of 10,000 ft. to 40,000 ft. The gas supply for the supply lines is guaranteed by the parallel connection of the pressure regulators even in case of failure of one of the pressure regulators. 
     An advantageous application of a pressure-limiting valve according to another aspect of the invention includes a method of gas distribution in an airplane gas distribution system using a pressure-limiting means with two parallel lines with two pressure-limiting valves each arranged in the same direction in series. 
     An exemplary embodiment of the present invention is shown in the drawings and will be explained in greater detail below. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which a preferred embodiment of the invention is illustrated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  schematically shows a gas distribution system, 
         FIG. 2  shows a doubly redundant pressure-limiting means according to the present invention, and 
         FIG. 3  shows a shut-off device on a pressurized gas cylinder with a limit switch. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings in particular,  FIG. 1  schematically shows a gas distribution system  1  for oxygen in an airplane, which airplane is not specifically shown in FIG.  1 . The system has three pressurized gas cylinders  2  for oxygen as the pressurized gas source and downstream cylinder pressure reducers  3 , a pressure-limiting means  4 , two pressure regulators  5  connected in parallel, and a branching site  6 , from which a first supply line  7  is supplied with oxygen via a first shut-off valve  8  and a second supply line  9  is supplied with oxygen via a second shut-off valve  10 . Emergency oxygen supply means  11  with breathing masks  12  and flow-limiting valves  14  are located at the supply lines  7 ,  9 . When the emergency oxygen supply means  11  are activated, the flow of gas into the breathing masks  12  is also released via shut-off valves  82  and gas-metering means  92 . The free ends of the supply lines  7 ,  9  are connected via a first nonreturn valve  16  and a second nonreturn valve  15  to a return line  17  and to a third supply line  18 , at which emergency oxygen supply means  19  are likewise located. 
     A fourth supply line  20  and a fifth supply line  21 , which likewise supply oxygen to emergency oxygen supply means  22 , extend in the front part of the airplane, which is not shown specifically. 
     The first supply line  7  and the second supply line  9  are located at the level of the engines, i.e., at the level of the so-called “engine burst area.” 
     An evaluating device  23  is connected to the shut-off valves  8 ,  10 , the pressure regulators  5  as well as a pressure-measuring means  24  determining the pressure between the supply lines  7 ,  9 . A central computer unit  25 , which performs all control and monitoring tasks, receives control and measured signals from the control means  24  and from limit switches  26 , which are located at shut-off valves  27  of the pressurized gas cylinders  2 . 
     The gas distribution system  1  described in the present invention operates as follows: 
     After the opening of the shut-off valves  27  at the pressurized gas cylinders  2 , the central computer unit  25  receives the information via the limit switches  26  that the oxygen supply is ready to operate. Pressure is admitted to the supply lines  7 ,  9 ,  18 ,  20  and  21  via the cylinder pressure reducers  3 , the pressure regulators  5  and the branching site  6  in case of decompression of the cabin, so that the emergency oxygen supply means  11 ,  19 ,  22  are ready for use. The differential pressure between the first supply line  7  and the second supply line  9  is measured with the pressure-measuring means  24 . The shut-off valves  8 ,  10  are also opened during normal operation. Thus, essentially the same pressure prevails in the supply lines  7 ,  9 ,  18 ,  20 ,  21 , so that the evaluating device  23  receives the information from the pressure-measuring means  24  that there is no differential pressure. Even though a pressure drop does occur within the entire system because of the removal of gas when the emergency oxygen supply means  11 ,  19 ,  22  is switched on, no appreciable differential pressure is measured as yet between the supply lines  7 ,  9  because of the essentially equal number of breathing masks within the first supply line  7  and the second supply line  9 . 
     If the first supply line  7  is damaged by an engine part flying around, which is not shown in  FIG. 1 , in the area of the supply lines  7 ,  9 , i.e., in the area of the “engine burst area”, the pressure-measuring means  24  detects a differential pressure because of the escaping oxygen, and the evaluating device  23  determines that the limit value of the differential pressure has been exceeded. The switching threshold for sending a closing signal to the first shut-off valve  8  is in a range between about 50 mbar and 200 mbar. The third supply line  18  is supplied with gas in this case via the second supply line  9  and the second nonreturn valve  15 . The nonreturn valves  15 ,  16  are arranged in opposite directions in relation to one another, so that gas can flow off only from the supply lines  7 ,  9  into the return line  17  but not in the opposite direction. 
     Thus, there is no total loss of gas in case of damage to one of the supply lines  7 ,  9 , but the intact supply lines  9 ,  18 ,  20 ,  21  can continue to be able to be supplied with oxygen. When the gas reserve of the pressurized gas cylinders  2  is depleted, these can be refilled via a central filling connection  13 . 
       FIG. 2  schematically illustrates the design of the pressure-limiting means  4  according to the present invention between the cylinder pressure reducers  3  and the pressure regulators  5 . Two nonreturn valves  43 ,  44  spring-loaded in the same direction are arranged in a first line  41 , and a second line  42 , which is connected in parallel to the first line  41 , contains the nonreturn valves  45 ,  46 . All nonreturn valves  43 ,  44 ,  45 ,  46  have the same opening pressure. If, e.g., the valve body in the nonreturn valve  43  is blocked, so that the valve cannot open, the overpressure is limited via the nonreturn valves  45 ,  46 . If gas can flow freely through the nonreturn valve  43  as a consequence of a valve body jammed in the open position, the nonreturn valve  44  assumes the overpressure limitation. The overpressure limitation is also guaranteed via the remaining, intact nonreturn valves in case of failure of a nonreturn valve in one of the lines  41 ,  42  each. Besides the first case of error, the second case of error is also covered with the pressure-limiting means described in the present invention. 
       FIG. 3  schematically illustrates the shut-off valve  27  with a handwheel  28  on the pressurized gas cylinder  2 . If the handwheel  28  is rotated in the direction of arrow  29  into the open position, the reaching of the end position is detected with the limit switch  26 . The central computer unit  25 ,  FIG. 1 , receives the information via the limit switch  26  that the corresponding shut-off valve  27  has been opened. 
     While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.