Abstract:
A valve assembly comprises a housing, a movable member, a fixed member, and a resilient member. The seat element has an upstream side, a downstream side, and an outlet port providing fluid communication therebetween, with the seat element fixed in a flow control segment adjacent a valve outlet. The drain element, operable between a first axial position closest to an inlet structure, and a second axial position abutting an upstream surface of the fixed seat element, is retained upstream from the fixed seat element and includes an upstream side, a downstream side, and a plurality of inlet ports through the drain element providing fluid communication therebetween. The resilient element is disposed axially within a middle fluid chamber defined by a portion of the flow control segment located between the fixed seat element and the movable drain element, the resilient element applying a first biasing force to urge the drain element upstream toward the first position, urging the valve into an open, flow permissive configuration.

Description:
BACKGROUND 
       [0001]    The combustor of a gas turbine engine ignites fuel mixed with compressed air in one or more combustion chambers, and maintains controlled burning of the air-fuel mixture. The combustion products are directed into the turbine section, where it is then exhausted through a nozzle or pipe to drive one or more turbine stages. To ensure rapid and reliable startup, the combustor chamber(s) must be vented or drained of unburned fuel. Unburned fuel can accumulate in the combustor before or after operation due to minor leaks from fuel lines, failed starts, and the like. At the same time, it is desirable that any vent or drain minimize or prevent compressed air from escaping during engine operation. 
         [0002]    To address this issue, combustors typically include a drain valve downstream from the combustor chamber(s) to direct excess liquid to an overboard drain. The drain valve permits flow when the engine is not operating, and restricts flow when the engine is active. Current drain valves are subject to jamming and premature failure, leading to bleeding of compressor air overboard during engine operation and incomplete drainage when the engine is offline. This complicates the ability to build an efficient and fail resistant valve. 
       SUMMARY 
       [0003]    A valve assembly comprises a housing, a movable member, a fixed member, and a resilient member. The housing includes a central bore extending through the housing with a central flow control segment disposed axially between an inlet fitting segment and an outlet fitting segment. The seat element has an upstream side, a downstream side, and an outlet port proximate a center of the seat element providing fluid communication therebetween, with the seat element fixed in the flow control segment adjacent the outlet fitting segment. The drain element is retained upstream from the fixed seat element and includes an upstream side, a downstream side, and a plurality of inlet ports through the drain element providing fluid communication therebetween. The drain element is operable between a first axial position closest to the inlet fitting segment, and a second axial position abutting an upstream surface of the fixed seat element, with the first axial position defining a first, flow-permissive configuration for the valve assembly, and the second axial position defining a flow-restrictive configuration for the valve assembly. The resilient element is disposed axially within a middle fluid chamber defined by a portion of the flow control segment located between the fixed seat element and the movable drain element, the resilient element applying a first biasing force to urge the drain element upstream toward the first position, urging the valve into the open, flow permissive configuration. 
         [0004]    A valve drain element comprises a drain element body, a bias receiving surface, a recessed structure, and a fluid isolation structure. The substantially cylindrical body is configured for axial movement along a valve bore between a first upstream position and a second downstream position. The body includes an upstream side, a downstream side, and a plurality of ports providing fluid communication therebetween. The body is sized to direct fluid flow exclusively through the plurality of ports instead of around an outer diameter of the drain element. The bias receiving surface forms a portion of the downstream side of the body, and is configured to axially direct a first applied biasing force urging the drain element toward the first upstream position. The recessed structure on the upstream side of the body is configured to concentrate and direct fluid pressure received from an upstream source into a second biasing force opposing the first biasing force. The fluid isolating structure projects generally perpendicular to the body from the downstream side and is configured to abut a second fluid isolating structure when the drain element is in the second downstream position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1A  schematically depicts a perspective cross-section of a combustor drain valve in an open configuration. 
           [0006]      FIG. 1B  is a perspective cross-section of the combustor drain valve in a closed configuration. 
           [0007]      FIG. 2  is a plan cross-section of the combustor drain valve housing. 
           [0008]      FIG. 3A  depicts a perspective view of a movable drain element. 
           [0009]      FIG. 3B  is a plan cross-section of the movable drain element from  FIG. 3A   
           [0010]      FIG. 4A  shows a perspective view of a fixed valve seat element. 
           [0011]      FIG. 4B  is a plan cross-section of the fixed valve seat element from  FIG. 4A . 
       
    
    
     DETAILED DESCRIPTION 
       [0012]      FIGS. 1A and 1B  show perspective cross-sections of a combustor drain valve  10  in respective open (drain) and closed (sealed) positions. The valve  10  includes housing  12 , bore  14 , valve inlet section  16 , valve outlet section  18 , connecting flanges  20 , movable drain element  22 , fixed valve seat element  24 , resilient spring element  26 , middle chamber  28 , retaining ring  30 , drain element ports  32 , valve seat port  34 , and drain element recess  36 . 
         [0013]    Combustor drain valve  10  regulates drainage of excess unburned fuel from a combustor of a gas turbine engine (not shown). The operation of gas turbine engines are well known, with the combustor section being disposed between a compressor section and a turbine section. The gas turbine engine, for example, can be an industrial gas turbine or can be secured to an aircraft either to provide motive power or to provide supplemental electric, hydraulic, or pneumatic power as an auxiliary power unit (APU). 
         [0014]    During startup or shutdown, or even occasionally while the engine is wholly inactive, excess fuel can accumulate in the combustor which must be drained to ensure safe starts and prevent fires. Fuel can build up in the combustor chambers for several reasons including failed starts, small leaks from fuel control valves, etc. Valve  10  is thus configured in  FIG. 1A  to drain this excess fuel when the engine is off. Valve  10  is automatically closed when combustion chambers are pressurized to prevent loss of compressed air and fuel during engine operation. This configuration is shown in  FIG. 1B . 
         [0015]      FIG. 1A  shows drain valve  10  in an open (drain) configuration with housing  12  and bore  14 . Inlet section  16  and outlet section  18  are bolted or otherwise secured together at flanges  20 . Unburned fuel flows from the combustor chambers (not shown) into inlet section  16 . When valve  10  is in this open position, there is free communication between inlet section  16  and outlet section  18  via the operative section containing movable drain element  22 , fixed valve seat  24 , and resilient element  26  (shown in more detail in  FIGS. 3A and 3B ). Resilient element  26 , such as a spring, is disposed in middle chamber  28  and biases movable element  22  away from valve seat  24  and toward inlet section  16 . Valve seat  24  is held in place by a seat or recess in an operative section of bore  14 . Movable drain element  22  is prevented from being pushed out of bore  14  by retaining ring  30 , which is elastically or resiliently retained in a groove or other structure formed out of bore  14 . For example, retaining ring  30  is a ring or coil manufactured from resilient material similar to a spring like resilient element  26 . With this material, ring  30  tends to expand to a larger diameter in the absence of an applied force. Ring  30  is then installed by bending it such that the diameter is temporarily reduced, then when the bending force is removed, the resilient material reacts and expands against the outer diameter of bore  14 . As shown in  FIG. 2 , bore  14  can include a seat or recess to fix the axial position of retaining ring  30 . 
         [0016]    When inlet section  16  is not pressurized, there is no force to counter resilient element  26 , and thus movable drain element remains on the inlet side of valve  10  away from seat element  24 . Excess unburned fuel and potentially other fluids from the combustion chambers (not shown) are free to enter valve  10  via connection lines (not shown) leading to inlet  16 . This fluid then flows through bore  14  into middle chamber  28  via drain ports  32  extending axially through movable drain element  22 . The fluid is directed by the shape of drain ports  32 , which can also be tapered radially toward the center line of bore  14  to further facilitate drainage toward valve seat port  34  where the fluid eventually exits from outlet section  18 . Outlet section  18  typically includes fittings for connection to an overboard drain, but outlet  18  can alternatively lead to a fuel recovery system or similar apparatus (not shown). 
         [0017]      FIG. 1B  shows drain valve  10  in a closed (sealed) position. Valve  10  is closed when inlet section  16  is pressurized. Pressure, represented by arrow P, comes from combustor chambers (not shown) containing the pressurized air-fuel mixture. In  FIG. 1A , valve  10  was open due to resilient element  26  biasing movable drain element  22  away from valve seat  24 . Here, pressure P is applied to drain element recess  36 , which concentrates the force of pressure P over a smaller surface to oppose the biasing force of resilient spring element  26 , urging movable drain element  22  to abut valve seat element  24 . In this closed configuration of  FIG. 1B , contents of the combustor chamber are no longer free to escape via drain ports  32  and valve seat port  34 . Middle chamber  28  is now much smaller than was seen in  FIG. 1A , and access to outlet section  18  via valve seat port  34  is blocked by contact between surfaces of movable drain element  22  and valve seat  24 . Drain element  22  and valve seat  24  are shown in more detail in  FIGS. 3A-4B . 
         [0018]    Traditional drain valves utilize a ball-and-spring configuration to transition between open and closed configurations. In these prior valves, a spring is held between a pin at the inlet end and a valve seat at the outlet end of a bore with ball sitting at the inlet end of the spring adjacent the pin. During a non-operating condition, the combustor chamber(s) are unpressurized and the spring is intended to bias the ball against the pin to keep the valve open. Excess liquid and vaporized fuel then is to flow around the ball and out through the valve seat out of the bore. When the chamber is pressurized, the ball is to overcome the force of the spring to contact the seat blocking outlet flow. 
         [0019]    The old ball-and-spring style valve tends to have several failure modes, making it prone to premature wear and failure. Repeated engine cycles impart fatigue stresses on the spring, extending the length of the spring and reducing the biasing force holding open the valve. The spring then works its way out of the bore, or otherwise gets displaced and causes a jam. With the ball more likely to get caught up in the center of the spring, eventually the biasing force that previously pushed the ball back in its proper position against the pin as inlet pressure approached zero is lost. The ball can also become jammed inside the center of the spring after being weakened from fatigue. This phenomenon is referred to as “ball stacking”. 
         [0020]    Valve failure due to ball stacking allows compressed air to bleed out of the combustion chambers rather than being sealed off. This reduces available operating pressure and wastes fuel from reduced engine efficiency. Jamming of the valve in this manner renders it inoperable. In many cases, the old style valve can jam to such an extent that it will never completely open or close, leaving it permanently in a partially open state. The jammed valve cannot properly close because the ball is not in a place to react the compressed air from the inlet side of the valve, which flows around the ball as if the valve were open. When the prior art valve is stuck open, a fraction of the pressurized fuel-air mixture escapes the combustor through the jammed valve reducing efficiency from lost compressor work, fuel, and combustion energy. 
         [0021]    In contrast, movable drain element  22  of valve  10  prevents ball stacking by providing a rigid perpendicular structure onto which resilient spring element  26  can exert its biasing force toward inlet section  16 . Drain element  22  is sized to fit securely in bore  14  and includes a surface on the downstream side to prevent resilient element  26  from settling or slipping around the outer diameter of drain element  22 . The biasing force on drain element  22  in turn urges valve  10  toward the open position shown in  FIG. 1A . Thus, instead of the unburned fuel flowing around the outside of a ball, in valve  10  fluid travels through drain ports  32  into middle chamber  28 , and then out through valve seat  24  via center port  34 . Any liquid remaining in chamber  28  that does not immediately reach port  34  is eventually vaporized either by ambient conditions or by hot pressurized air from the operating combustor and eventually leaves chamber  28  through center port  34 . 
         [0022]    To maintain freedom of movement in bore  14 , movable drain element  22  can be periodically lubricated or include a self-lubricating seal, gasket, or other similar structure around its outer diameter. Alternatively or additionally, bore  14  can include a self-lubricating coating. One suitable material for lubricating the outer diameter of drain element  22  includes graphite. However, many other coatings and/or lubricants can be selected to adapt this type of valve to other applications depending on particular thermal, mechanical, and chemical compatibilities. 
         [0023]    Since it is much less likely for drain element  22  to jam or stick in resilient element  26  as compared to the prior ball-and-spring design, resilient spring element  26  can thus be stronger as compared to the prior design as well. This can extend the life of valve  10  because the risk of a stronger spring element  26  creeping or working its way out from behind movable drain element  22  is virtually nil, which minimizes the chances for valve  10  to jam and fail open. 
         [0024]    Resilient element  26  in this example is a coil spring manufactured from X-750 nickel alloy, widely available from a number of commercial vendors. However, resilient element  26  can take other forms that provide a biasing force against drain element  22  and can withstand the chemical and thermal stresses inherent in a combustor assembly while still maintaining its required mechanical properties. If valve  10  is adapted to another purpose, resilient element  26  will, of course, be modified to account for the correspondingly different severity of service. 
         [0025]      FIG. 2  shows the cross-section of valve housing  12  with bore  14 , inlet section  16 , outlet section  18 , flanges  20 , inlet fitting end  40 , outlet fitting end  42 , valve seat stage  44 , shoulder  46 , drain element stage  48 , and ring groove  50 . 
         [0026]    Valve housing  12  is oriented vertically in  FIG. 2  proximate the base of the combustor so as to facilitate drainage of unburned fuel mainly by gravity. Inlet section  16  and outlet section  18  each have respective fitting ends  40 ,  42  with relatively large internal diameters for coupling valve housing  12  to combustor chamber(s) and overboard drains (not shown). 
         [0027]    As described above, inlet section  16  and outlet section  18  are joined and secured together at flanges  20  to form housing  12  with continuous bore  14 . Bore  14  is machined with multiple sections or stages between fitting ends  40 ,  42  to facilitate installation and retention of the internal components. Furthest downstream and adjacent to outlet fitting end  42  is valve seat stage  44  and shoulder  46 . Together they are shaped with substantially the same height and outer diameter to receive and retain valve seat  24 . Stage  44  may be formed with a slightly larger diameter, however, to accommodate a seal between the outer diameter of seat  24  and the surface of stage  46 . Drain element stage  48  is upstream of stage  44  and has a slightly larger diameter to retain and accommodate axial movement of resilient element  26  and drain element  22 , which opens and closes the valve as shown in  FIGS. 1A and 1B . Finally, stage  48  also includes a larger diameter groove  50  to hold retaining ring  30 , also shown in  FIGS. 1A and 1B . In this example, ring  30  is manufactured with a resilient material similar to a spring (like resilient member  26 ) such that it tends to bias itself radially outward. As explained above, ring  30  can be installed by bending ring  30  radially upon itself to reduce the diameter. When the bending force is removed, the natural outward bias holds ring  30  within the confines of groove  50 . Ring  30  also includes a thickness greater than the depth of groove  50 . Thus, when retained in groove  50 , a portion of ring  30  remains in the flow path to retain drain element downstream of bore  14  and balance the biasing force provided by resilient element  26 . 
         [0028]    Housing  12  can be manufactured from any suitable hard material including most grades of corrosion resistant steel. One example method of assembling valve  10  is according to the following general description. Valve seat  24  (shown in  FIGS. 4A and 4B ) is inserted into valve seat stage  44 . The base of seat  24  is prevented from moving farther downstream due to the smaller diameter of downstream stage  44  and shoulder  46 . Drain element  22  (shown in  FIGS. 3A and 3B ) is inserted into inlet section  16  at stage  48  after placing retaining ring  26  into groove  50 . Resilient element  26  (shown in  FIGS. 1A and 1B ) is then inserted between drain element  22  and valve seat  24 , prior to inlet section  16  being secured to outlet section  18 . Resilient element  26  can optionally be secured to drain element  22  and/or seat  24  via one or more small hooks or similar structures on the appropriate surfaces. 
         [0029]      FIG. 3A  is a rear perspective schematic of the downstream side of drain element  22  with drain ports  32 , drain element recess  36 , rear drain isolating structure  52 , downstream surface  54 , and outer seal  56 .  FIG. 3B  is a plan cross-section of drain element  22  with drain ports  32 , recess  36 , drain isolating structure  52 , downstream surface  54 , outer seal  56 , and pressure directing surface  58 . 
         [0030]      FIG. 3A  shows the downstream side of drain element  22  with drain ports  32  radially arranged thereon, while the cross-sectional view in  FIG. 3B  shows two of these ports  32  extending axially through drain element  22 . Drain element  22  has a substantially cylindrical body that moves axially through bore  14  (as shown in  FIGS. 1A and 1B ). When drain element  22  is biased away from seat  24  (shown in  FIGS. 4A-4B ), ports  32  provide a path for fluids such as unburned fuel to drain from the combustor chambers (not shown) to valve seat port  34 , located at the center of seat  24 . Ports  32  can also be radially tapered to encourage more liquid to flow toward valve seat port  34 . Liquid being drained can also flow along drain isolating structure  52  toward port  34 . However, flow is restricted from going around drain element  22  because the cylindrical body is sized and configured to direct flow only through ports  32 . 
         [0031]    Drain isolating structure  52  engages against corresponding isolation structure  60  on valve seat  24  (shown in  FIGS. 4A and 4B ) to close the valve. Recall from  FIG. 1B  that pressure P is directed toward front pressure recess  36  on drain element  22 . As seen in  FIG. 3B , recess  36  includes pressure directing surface  58 . Structures  52  and  60  engage upon sufficient application of combustor pressure P to pressure directing surface  58  in recess  36 , closing off access and fluid communication between inlet section  16  and outlet section  18 . 
         [0032]    Drain ports  32  are small enough in diameter and can also be tapered radially to direct drainage of liquids toward the center line of valve  10  (and valve seat port  34 ). This shape and size also helps provide sufficient pressure differential to facilitate movement of drain element  22 . To further improve liquid drainage and movement of element  22 , ports  32  can also have a larger upstream opening and a smaller downstream exit. Movement is also facilitated by seal surface  56 . In this example, seal  56  is self-lubricating graphite or other material for simultaneously reducing friction and preventing leakage. 
         [0033]    In this example, drain element  22  is manufactured from SAE grade 410 corrosion resistant steel that has been heat treated for hardness. However, other alloys with similar or improved hardness and corrosion resistance can be readily substituted. As noted above, drain element  22  can also be provided with graphite seal  56  or a similar coating around its outer diameter to provide lubrication for axial movement of element  22  in bore  14 . 
         [0034]      FIG. 4A  is a perspective view of fixed valve seat  24  with center drain port  34  and surrounding seat isolation structure  60 .  FIG. 4B  shows a plan cross-section of valve seat  24 . As seen in  FIG. 1A , excess fuel and other fluids from combustion chambers (not shown) flow through center drain port  34  when valve  10  is open. And as seen in  FIG. 1B , valve  10  is sealed by moving drain element  22  toward seat  24  to block drain port  34 . Blockage is effected by engaging drain isolation structure  56  (shown in  FIG. 3B ) with seat isolation structure  58 . 
         [0035]    Valve seat  24  can be manufactured from any suitable material. In this example, drain element  22  is formed from austenitic low-carbon SAE grade 304L stainless steel. However, other alloys with similar or improved properties, such as SAE grades 321 or 347 can be readily substituted. 
         [0036]    This example embodiment of combustor drain valve  10  has been described in the context of a newly assembled combustor. It is apparent that valve  10  can also be readily adapted and used in a replacement or refurbishment capacity, particularly as a substitute and improvement over the aforementioned ball-and-spring valves. The drain valve can also be adapted for several other uses whereby a fluid is to be drained from one or more upstream chambers before the chamber is pressurized and the valve is to be closed. 
         [0037]    While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.