Abstract:
A minimum pressure shut-off valve closes off fuel flow responsive fuel pressure being below a predefined pressure. A sleeve includes at least a first flow window and a second flow window. The second window includes a notch providing a flow area based on an axial position of a spool moveable within the sleeve.

Description:
BACKGROUND 
       [0001]    A gas turbine engine typically includes a fan section, a compressor section, a combustor section and a turbine section. Air entering the compressor section is compressed and delivered into the combustion section where it is mixed with fuel and ignited to generate a high-speed exhaust gas flow. The high-speed exhaust gas flow expands through the turbine section to drive the compressor and the fan section. 
         [0002]    A fuel system for a gas turbine engine meters and controls fuel flow to the combustor and other portions of the gas turbine engine that utilizes fuel flow and pressure for operating actuators and other control elements. During startup and shutdown of the gas turbine engine fuel flow and pressure may be below desired levels for operation. It is desirable to prevent fuel flow to the gas turbine engine, actuators and other control elements until such time as required pressure and flow are present. It is therefore desirable to control and prevent fuel flow to the combustor and other elements of the gas turbine engine until such time as the fuel pressure and flow are within a predetermined operating range. 
       SUMMARY 
       [0003]    A disclosed fuel system for a gas turbine engine includes a minimum pressure shut-off valve for closing off fuel flow to an outlet in response to fuel pressure being below a predefined pressure. The shut-off valve includes a sleeve defining a bore that extends along an axis and includes at least a first flow window and a second window. The second window includes a notch for providing a flow area based on an axial position of a spool moveable within the sleeve. The spool controls or allows fuel flow through the first and second windows when fuel pressure is above a minimum level and closes off fuel flow below the minimum value. 
         [0004]    Although the different examples have the specific components shown in the illustrations, embodiments of this disclosure are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples. 
         [0005]    These and other features disclosed herein can be best understood from the following specification and drawings, the following of which is a brief description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a schematic view of an example gas turbine engine. 
           [0007]      FIG. 2  is a schematic view of an example fuel system for a gas turbine engine. 
           [0008]      FIG. 3  is an exploded view of an example minimum pressure shut-off valve. 
           [0009]      FIG. 4  is a cross-sectional view of the example shut-off valve in a closed position. 
           [0010]      FIG. 5  is a cross-section view of the example shut-off valve in an initial starting position. 
           [0011]      FIG. 6  is a schematic view of a window defined within a sleeve of the shut-off valve. 
           [0012]      FIG. 7  is a schematic view of another window defined within the sleeve of the example shut-off valve. 
           [0013]      FIG. 8  is a cross-sectional view of the example shut-off valve in an operational mode. 
           [0014]      FIG. 9  is a schematic view of a flow window of the shut-off valve in the operational condition. 
           [0015]      FIG. 10  is another view of another window including a notch in an example operational position. 
           [0016]      FIG. 11  is a cross-sectional view of the example spool. 
           [0017]      FIG. 12  is a cross-sectional view of the example spool and sleeve. 
           [0018]      FIG. 13  is a cross-sectional view of the example sleeve. 
           [0019]      FIG. 14  is a side view of the example sleeve. 
           [0020]      FIG. 15  is a sectional view through windows of the example sleeve. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]      FIG. 1  schematically illustrates an example gas turbine engine  10  that includes a fan section  12 , a compressor section  14 , a combustor section  16  and a turbine section  18 . Alternative engines might include an augmenter section (not shown) among other systems or features. The fan section  12  drives air along a bypass flow path B while the compressor section  14  draws air in along a core flow path C where air is compressed and communicated to a combustor section  16 . In the combustor section  16 , air is mixed with fuel and ignited to generate a high pressure exhaust gas stream that expands through the turbine section  18  where energy is extracted and utilized to drive the fan section  12  and the compressor section  14 . In this example, the turbine section  18  drives the fan section  12  through a geared architecture  15  such that the fan section  12  may rotate at a speed different than the turbine section  18 . 
         [0022]    Although the disclosed non-limiting embodiment depicts a turbofan gas turbine engine, it should be understood that the concepts described herein are not limited to use with turbofans as the teachings may be applied to other types of turbine engines; for example a turbine engine including a three-spool architecture in which three spools concentrically rotate about a common axis and where a low spool enables a low pressure turbine to drive a fan via a gearbox, an intermediate spool that enables an intermediate pressure turbine to drive a first compressor of the compressor section, and a high spool that enables a high pressure turbine to drive a high pressure compressor of the compressor section  14 . 
         [0023]    The example gas turbine engine includes a fuel system  20  that supplies fuel from a fuel supply to the combustor section  16  and also to other devices within the gas turbine engine that may utilize fuel for heat exchanging or for powering actuators. 
         [0024]    Referring to  FIG. 2 , the example fuel system  20  is schematically illustrated and includes a fuel pump  24  that receives fuel from a fuel supply  22 . The fuel pump  24  includes an inlet  32  that draws fuel from the fuel supply  22  and also receives fuel that may be bypassed or drained from the fuel system  20 . The example fuel system  20  includes a minimum pressure shut-off valve  30  and also other control valves schematically illustrated at  28 . The minimum pressure shut-off valve  30  shuts off fuel flow from the fuel system  20  to the combustor section  16  or other devices within the gas turbine engine  10  when a fuel pressure and flow falls below a predetermined minimum. 
         [0025]    Accordingly, during operation and specifically during start-up and shut-down operation, fuel flow is shut-off to the combustor section  16  until such time as pressure and flow is above the predetermined minimum. The predetermined minimum fuel pressure and flow is that level desired for combustion and operation of other features of the gas turbine engine  10  ( FIG. 1 ). 
         [0026]    Referring to  FIGS. 3 and 4 , an example shut-off valve  30  includes a main housing  34  within which is disposed a sleeve  46  and a spool  50 . The sleeve  46  is held against a forward surface  65  of the main housing  34  by a cap  38 . The example cap  38  includes threads  66  that engage complementary internal threads  64  defined within the main housing  34 . The cap  38  is threaded into the main housing  34  to hold the sleeve  46  against the forward surface  65  and a face seal  54  disposed within a chamber  56  of the main housing  34 . 
         [0027]    The cap  38  also holds a spring  40  against the spool  50  disposed within the sleeve  46 . The spring  40  is held in place on an end opposite the spool  50  by a spring seat  42 . The example spring seat  42  is threaded into threads  68  in the cap  38  such that it can be adjusted to provide an adjustment of the biasing force provided by the spring  40 . The spring biases the spool  50  towards a closed position shown in  FIG. 4 . A plug  44  is threaded into the cap  38  to seal off the opening interface through the thread  70  of the spring seat  42  is received within the cap  38 . 
         [0028]    The spool  50  is received within a bore of the sleeve  46  and is movable responsive to pressure differences between an inlet  58 , an outlet  60 , and a control port  62  defined within the main housing  34 . The control port  62  communicates fluid pressure to a back side of the spool  50 . Fuel entering the inlet  58  will proceed through windows defined in the sleeve  46  and then through the outlet  60 . The specific axial relationship of the spool  50  relative to the sleeve  46  uncover windows  78 ,  76  defined within the sleeve  46  to govern fluid flow between the inlet  58  and the outlet  60 . A spool seal  52  is disposed between the spool  50  and the sleeve  46 . A sleeve seal  48  is disposed between the sleeve  46  and the main housing  34 . 
         [0029]    The spring  40  exerts a biasing force on the spool  50  that drives the spool  50  against the face seal  54 . The face seal  54  is disposed within a groove defined within the main housing  34  at the forward surface  65 . The sleeve  46  also engages the face seal  54  to prevent fuel flow around the sleeve  46 . Accordingly, fuel flow must flow from the inlet  58  through windows  76 ,  78  defined in the sleeve  46  and out the outlet  60 . The spool  50  selectively blocks the windows  76 ,  78  defined within the sleeve  46  to govern and regulate fluid flow through the outlet  60 . 
         [0030]    The disclosed shut-off valve  30  is actuateable responsive to a pressure differential across the spool  50  in combination with the biasing force provided by the spring  40 . Pressure is communicated to through the control port  62  to a back side of the spool  50 . Fuel pressure at the inlet  58  must rise to a level above the combined forces provided by the fuel pressure and spring force on the spool  50 . The shut-off valve  30  is shown in  FIG. 4  in a closed position. In the closed position, the spring force and pressure forces are at an imbalance condition that holds the spool against the face seal  54  to prevent fuel flow. 
         [0031]    Referring to  FIG. 5 , the example shut-off valve  30  is shown in an initial startup position. In the initial startup position, fuel pressure at the inlet is increased to generate an imbalance that lifts the spool  50  off the face seal  54  such that a passageway from the inlet  58  to the outlet  60  is provided. 
         [0032]    Referring to  FIGS. 6 and 7  with continued reference to  FIG. 5 , the example sleeve  46  includes four windows, two without a notch indicated at  76  and two that includes a notch  84  indicated at  78 . Each of the windows  76 ,  78  includes a generally oval shape. The notched window  78  includes the notch  84  that extends axially forward of the oval shaped common with windows  76 . 
         [0033]    In an initial startup position illustrated in  FIG. 5 , the spool  50  moves axially rearward off of the face seal  54  to uncover the notch portion  80  of the window  78 . Accordingly, the notch portion  80  provides the fuel flow area  84  from the inlet  58  through the outlet  60 . The remaining portions of the windows  76 ,  78  are blocked as indicated at  86 . In this position, only the windows  78  that includes the notch  80  accommodates fuel flow between the inlet  58  and the outlet  60 . The other windows  76  remain blocked and do not allow fuel flow. 
         [0034]    Referring to  FIGS. 8 ,  9 , and  10 , the control shut-off valve  30  is shown in a partially open position where the forces exerted on the spool valve  50  are in a balanced condition such that the spool valve  50  has opened more flow area for flow between the inlet  58  and the outlet  60 . In this example, the spool  50  is moved such that not only are the notches  80  unblocked but also a portion of the windows  76  and  78  are open to fuel flow. 
         [0035]    The axial stroke of the spool  50  indicated at  88  corresponds to a desired flow area of the windows  76 ,  78  open to fuel flow between the inlet  58  and outlet  60 . In one non-limiting dimensional embodiment, the axial stroke  88  of the spool  50  is approximately 0.040 inches (1.016 mm) The axial stroke corresponds within an opening flow area  84  between all of the windows  76 ,  78 . In this example, the axial position of the spool  50  is related to the opening area  84  of the flow window  76 ,  78  by a ratio between 0.000 and 1.2600. In another disclosed example embodiment an axial position of the spool is related to the opening area by a ratio between 0.000 and 1.2438. 
         [0036]    Referring to  FIGS. 11-15 , the example spool  50  and sleeve  46  are shown in cross-section. The total stroke range  82  of the spool  50  relative to the sleeve  46  provides the desired gain in fuel pressure relative to the axial position. The example sleeve  46  includes the four windows  76 ,  78 , although a different number of windows could be utilized and is within the contemplation of this invention to provide the desired flow area relative to an axial position of the spool  50 . 
         [0037]    The sleeve  46  includes a bore  75  having a diameter  72  that corresponds with an outer diameter  92  of the spool  50  to provide a clearance. The clearance between the spool  50  and the sleeve  46  prevents leakage past the spool  50  while allowing movement within the bore  75 . In one disclosed example, a ratio between the bore diameter  72  and the outer diameter  92  of the sleeve  50  is between 0.9980 and 0.9990. In another disclosed example, the ratio of the bore diameter  72  to the outer diameter  92  of the spool  50  is between about 0.9994 and 0.9996. 
         [0038]    The clearance between the spool  50  and the bore  75  defines an annular spacing related to the outer diameter of the spool  50 . In one non-limiting dimensional embodiment, the clearance between the bore diameter  72  and outer diameter  92  of the spool  50  is between about 0.0002 and 0.0007. The clearance further defines a leakage path between the spool  50  and the bore diameter  72 . A ratio of the clearance to an outer diameter  92  of the spool is indicative of the leakage path. In one disclosed example embodiment, a ratio between the clearance  94  and the outer diameter  92  of the spool is between about 0.0009700 and 0.0009800. In another example embodiment, a ratio between the clearance  94  and the outer diameter  92  is between about 0.000976 and 0.0009798. 
         [0039]    The example spool  50  includes a seal surface  90  engages the face seal  54  to provide an effective seal diameter  96 . The seal diameter  90  accounts for pressures and forces that provide the desired seal desired for shutting off fuel flow at a minimum pressure level. In this example, the minimum seal diameter is balanced between the surface  90  and the face seal  54 . The example seal diameter is related to the outer diameter of the spool  50  according to a ratio of the seal diameter  96  to the outer diameter  92  of the spool  50  that is between about 0.8100 and 0.8350. In another disclosed example, a ratio of the seal diameter to the outer diameter  92  is between about 0.8150 and 0.8344. 
         [0040]    Accordingly, the example shut-off valve  30  controls fuel flow to maintain a minimum pressure desired for operation. Moreover, the example shut-off valve  30  stops fuel leakage from the system during shutdown and startup operations. 
         [0041]    Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that this disclosure is more than just a material specification and that certain modifications would come and are contemplated within the scope of this disclosure. For that reason, the following claims should be studied to determine the scope and content of this disclosure.