Abstract:
The present invention refers to a dual pressure regulation system to ensure a proper pressure regulation during the Aerial REFUELING operations with Hose and Drogue systems. More specifically is directed to dual redundant fuel pressure regulation systems. The pressure regulator system comprises two pressure regulators ( 10, 20 ) located in series and a control element ( 30 ) for controlling the movement of both regulators operatively connected downstream ( 34 ) the second pressure regulator ( 20 ) such that the movement of the pressure regulators ( 10, 20 ) is independently controlled by the control element ( 30 ) according to the delivery pressure downstream the second regulator ( 20 ).

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention is directed to a dual pressure regulation system for aerial refueling operations. The invention is intended to ensure a proper pressure regulation during the aerial refueling operations with hose and drogue systems. More specifically is directed to dual redundant fuel pressure regulation systems. The invention is also intended to cover refueling couplings for use by tanker aircraft for aerial refueling fitted with the dual pressure regulation system. 
       BACKGROUND OF THE INVENTION 
       [0002]    Aircraft include complex fuel systems that route aviation fuel from fuel tanks to aircraft systems that use the fuel. In the case of an aerial refueling, these systems can also include the fuel lines, manifolds and associated valving necessary for delivering fuel to a receiver aircraft. 
         [0003]    Aerial REFUELING hoses are equipped with couplings at their end to allow a proper fit of the receiver aircraft. 
         [0004]    Standard couplings are in accordance with the standard MIL-PRF-81975 and the historical standard MIL-C-81975. The current state of the art is based on MA-4 couplings. Those couplings have the mechanical interfaces defined by the military standard and, in general, comply with the performance requirements. 
         [0005]    In terms of pressure regulation, current MA-4 couplings are equipped with two regulators which are located in series in a channel. The main regulator is exposed to the outlet or delivery pressure such that it is the regulator responsible for supplying said required outlet pressure. The other regulator or auxiliary regulator helps the main regulator in supplying high flows providing an additional pressure in the main regulator such that the main regulator is able to avoid its throttle. 
         [0006]    The main regulator moves depending on the outlet pressure because it is directly exposed to it. When the pressure difference between the ambient pressure, measured through a port, and the delivery pressure exceeds a target value, the main regulator closes and when the difference is less, it is opened. Therefore the main regulator balances its position based on the balance of pressures on a restricting element. 
         [0007]    The auxiliary pressure regulator is located before the main regulator so it is not exposed to the delivery pressure. The auxiliary pressure regulator, depending on the flow and on the inlet pressure, increases the downstream pressure to conform the operation range of the main regulator, preventing its throttle. 
         [0008]    In fact, both regulators are needed to supply the required pressure. A drawback of current MA-4 couplings is that they are not able to independently achieve the delivery pressure requirement, this meaning that in the case of one pressure regulator failure, the system might not deliver the fuel at the required pressure causing potential damages on receiver pipelines. 
         [0009]    Therefore, said coupling is not redundant as the working of both regulators is not independent and moreover in case of single failure the coupling is not able to properly regulate the delivery pressure. 
         [0010]    Another drawback is that the failure of one of the regulators is a hidden failure only detected during routine maintenance tasks. 
         [0011]    On the other hand, the high pressure drop of the current designs for MA-4 coupling is penalising the system performances due to narrow passages and sharp edges in the interior walls. Preliminary issues of the standard MIL-PRF-81975 specified lower values for the acceptable pressure drop which had to be increased to allow the fulfilment by the industry. 
         [0012]    Currently there is a need in industry to have new couplings which ensure a full dual pressure regulation, however no system has been developed yet to ensure full redundancy on the pressure regulation system components. 
       SUMMARY OF THE INVENTION 
       [0013]    The above mentioned drawbacks are solved by the claimed dual pressure regulation system. 
         [0014]    A failure in the aerial refueling coupling pressure regulation system might be hazardous for the receiver aircraft pipelines. Therefore, dual pressure regulation in terms of redundancy is of utmost importance for the claimed invention. 
         [0015]    The dual pressure regulator system as previously described in the background of the invention comprises a channel having an inlet and an outlet, a first pressure regulator and a second pressure regulator, being said first and said second pressure regulator located in series lengthwise said channel such that in use the fuel flow goes through both regulators. 
         [0016]    As previously explained the inlet would be connectable to pipelines to a tanker aircraft and the outlet to pipelines to a receiver aircraft. 
         [0017]    Moreover, the first pressure regulator comprises a first restricting element linearly movable into the channel throughout the positions between a first position and a second position configured to allow a first pressure drop through the inlet of the channel when in the first position and a second pressure drop in the second position. 
         [0018]    The second pressure regulator comprises a second restricting element linearly movable into the channel throughout the positions between a first position and a second position configured to allow a first pressure drop through the outlet of the channel when in the first position and a second pressure drop in the second position. 
         [0019]    The dual pressure regulator system object of the invention is characterized in that it further comprises a control element for controlling the movement of the first and the second pressure regulators. Said control element is operatively connected downstream the second pressure regulator for measuring the delivery pressure to the receiver aircraft. Therefore the first, the second pressure regulators and the control element are configured such that the movement of the first and the second pressure regulators is controlled by the control element according to the delivery pressure to the receiver aircraft downstream the second regulator. 
         [0020]    The dual pressure regulation system object of the invention comprises two pressure regulators independently driven, located in series, but acting according to the delivery pressure measured downstream to both. The target pressure for both pressure regulators is the delivery pressure and said delivery pressure is the pressure which controls the position of each pressure regulator. In this way, it is possible to ensure the delivery pressure within the required range even with one regulator failed. 
         [0021]    Under standard conditions, the first regulator will work in normal conditions and in case of failure of said first regulator, the second regulator would start working. 
     
    
     
       DESCRIPTION OF THE FIGURES 
         [0022]      FIG. 1  is a schematic cross section of a known pressure regulation system. 
           [0023]      FIG. 2  is a schematic cross section of an embodiment of the invention. 
           [0024]      FIG. 3  is a schematic cross section of the embodiment shown in  FIG. 2  showing the second regulator working and the first regulator in stand-by. 
           [0025]      FIG. 4  is a schematic cross section of the embodiment shown in  FIG. 2  showing the system working after a surge pressure. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0026]    An embodiment of the claimed invention consists of a new pressure regulation system to be fitted in couplings in accordance with standard MIL-PRF-81975. 
         [0027]      FIG. 1  discloses a pressure regulator system of the state of the art. This device comprises two regulators ( 10 ,  20 ) located in series, a main regulator corresponding to the second pressure regulator ( 20 ) as it is the downstream regulator and an auxiliary regulator corresponding to the first pressure regulator ( 10 ) as it is the upstream regulator. 
         [0028]      FIGS. 2 to 4  discloses an embodiment of the claimed invention. Under standard conditions the first pressure regulator ( 10 ) is working and the second pressure regulator ( 20 ) is completely opened and in case the pressure drifts the second regulator ( 20 ) which is completely opened starts working. 
         [0029]    As shown in  FIG. 2  the first pressure regulator ( 10 ) would be stable within a tight pressure range around the nominal operating delivery pressure. If the delivery pressure becomes higher than the expected value, an inlet fuel pressure line ( 31 ) is piloted by the control ( 30 ) to close the first pressure regulator ( 10 ). If the delivery pressure becomes below the operational range, the first pressure regulator ( 10 ) is piloted to open. 
         [0030]    Embodiment of  FIG. 2  also discloses that the system further comprises a chamber ( 22 ) located into the channel ( 1 ) which is operatively connected to the first restricting and the second restricting element ( 11 ,  21 ) such that both elements ( 11 ,  21 ) are linearly movable with respect to said chamber ( 22 ). 
         [0031]    Said chamber ( 22 ) comprises two separated cavities ( 23 ,  24 ) each one operatively connected to each restricting element ( 11 ,  21 ) and is divided into two subcavities ( 25 ,  26 ,  27 ,  28 ) by an extended part ( 12 ,  13 ) of the restricting elements ( 11 ,  21 ) capable of sliding in each cavity ( 23 ,  24 ). 
         [0032]    The system also comprises different pressure lines ( 32 ,  33 ) for feeding each subcavity ( 23 ,  24 ). In that way every restricting element ( 11 ,  21 ) is independently controlled by the control element ( 30 ). 
         [0033]    The first pressure regulator ( 10 ) is declared as failed if the delivery pressure reaches a fixed value over the nominal delivery pressure and the first pressure regulator ( 10 ) is not being commanded to close. At that case, the second pressure regulator ( 20 ) starts working in a similar way to the first pressure regulator ( 10 ). 
         [0034]    As the second pressure regulator ( 20 ) is fed with independent pressure lines ( 33 ) redundancy is achieved. 
         [0035]    Moreover the system also comprises the inlet fuel pressure line ( 31 ) to pressurize each cavity ( 23 ,  24 ) and a downstream pressure line ( 34 ) which operatively connect the control element ( 30 ) to the delivery pressure. 
         [0036]    Additionally, the control element ( 30 ) is located outside the channel ( 1 ) at an external manifold. 
         [0037]    The embodiment object of the invention also allows the detection of a first pressure regulator ( 10 ) failure. 
         [0038]    The embodiment shown in  FIG. 3  shows that the control element ( 30 ) comprises a failure indicator ( 36 ) which is equipped with an indication for the case of the second pressure regulator ( 20 ) working at operational conditions. This allows assessing during post flight maintenance tasks whether the first pressure regulator ( 10 ) has been declared failed. 
         [0039]    More specifically, an auxiliary line ( 35 ) connected to the pressure line ( 33 ) of the second pressure regulator ( 20 ) is provided, said auxiliary line ( 35 ) feeds a visual indicator. 
         [0040]    Another advantage of the present pressure regulation system is that during the receiver disconnection, the coupling is exposed to high pressure surges which have to be dumped. Those surges run through the coupling from the receiver aircraft to the tanker airdraft. To react against these surges, the pressure regulation system independently commands the two pressure regulators ( 10 ,  20 ) to close as soon as a pressure over the maximum working value is detected downstream the second regulator ( 20 ). This surge relief sub-system commands to close the pressure regulators ( 10 ,  20 ) with fuel pressure from the coupling downstream point (where the surge is started) and, in order to be quick enough, the fuel pressure flows to the cavities ( 23 ,  24 ) through feeding line ( 38 ) coming from downstream the second pressure regulator ( 20 ) as shown in  FIG. 4 . 
         [0041]    The external control element ( 30 ) will be fixed to the channel ( 1 ), as a ‘dressing’, and it will be connected to the different cavities ( 23 ,  24 ) through pipes ( 32 ,  33 ) and holes along the struts which support the channel ( 1 ). Another advantage of the invention is that part of the hydro-mechanical elements, intended to move the pressure regulators ( 10 ,  20 ), have been taken out of the fuel path being outside the channel ( 1 ) and therefore, the area dedicated for the fuel way is wider, reducing the pressure drop. On the other hand, as far as part of the hydro-mechanical elements of the regulation mechanism has been placed outside to the channel ( 1 ), the regulator failure can be monitoring as previously stated. This represents an important advantage in terms of reduction of scheduled maintenance tasks. 
         [0042]    As shown in the embodiment of  FIGS. 2 to 4 , both pressure regulators ( 10 ,  20 ) comprises two poppet valves. Other configurations would be possible, such as for instance mushrooms valves. 
         [0043]    The channel ( 1 ) shown in the figures is cylindrical and also the inlet ( 2 ) and outlet ( 3 ). Also the chamber ( 22 ) is cylindrical that leading to a less pressure drop compared with other couplings of the state of the art, that improving the system performances. 
         [0044]    It is also an object of the present invention the coupling comprising a system according to one of the preceeding technical features.