Patent Publication Number: US-2007102341-A1

Title: Combination wash and barrier filter

Description:
BACKGROUND OF THE INVENTION  
      This invention relates to a wash flow filter for fuel filtration which utilizes plural parallel tubes.  
      Fuel systems, in particular for aircraft applications, require relatively clean fuel. Wash flow filters are commonly used in fuel systems to provide maintenance free systems for filtering contaminants from fuel. The filters are typically cylindrical or conical in shape. Fluid flow enters the cylinder at one end and flows out an opposing end. The cylinders are formed from a screen material to act as a filter. As the fluid flows through the cylinder some of the fluid passes radially out through the screen. Contaminants within the fuel are caught by the screen and remain within the cylinder. The fluid that has exited radially from the cylinders is filtered fuel. As other fluid flow continues to pass along the cylinder, it removes the contaminants from the screen to provide a self-cleaning filter.  
      The requirements of the fuel system determine the size of the wash flow filters. The surface area of the screen governs the amount of filtration obtained by the filter. Additionally, the velocity of the fluid passing through the filter is critical for washing the contaminants from the filtering material. Fluid velocity is controlled by the diameter of the cylinder. Therefore, the velocity required for flushing the contaminants dictates the diameter of the filter. Because the diameter of the tube is limited, the variable for controlling the amount of filtration is the length of the cylinder.  
      As fuel system become more complex the amount of filtration required increases. Higher levels of filtration cause the length of the cylinder the filters to increase. Fitting the required filter within the available system space becomes a problem as the filter lengthens.  
      A wash flow filter that does not require increasing length to maintain a desired fluid velocity and filtration level is needed.  
     SUMMARY OF THE INVENTION  
      The fuel filter assembly of the present invention includes multiple tubes within a wash flow filter. The filter is assembled within a bore. Multiple tubes run from a first header to a second header. A first seal is located in the first header to prevent fluid outside the bore and within the tubes from mixing with fluid inside the bore and outside of the tubes. The second header has a second seal similar to the first seal.  
      Fluid enters the filter at a first end and exits the filter at a second end. The tubes are manufactured of a mesh or filter material. Thus, as flow passes through the tubes some of the fluid exits radially through the sidewalls of the tubes. The sidewalls filter particles out of the fluid as the fluid passes through to obtain a filtered fluid. As more fluid flows along the fluid path the particles blocked by the sidewalls are washed out the second end of the tube. Thus, the filter is self-cleaning. The washed fluid that has exited the tubes sidewalls is directed to a device requiring filtered fluid, such as an engine.  
      The fuel filter assembly has two distinct operating modes a conventional wash flow mode and a barrier filter mode. In “barrier” mode the axial flow through the filter is shut off forcing all flow to pass through the screen radially. During this time period, the screen collects all the contaminant that is larger than the minimum screen opening and proceeds to become clogged until the axial motive flow is re-instated allowing the wash mode to be re-established. Within a short period of time the screen is washed fully clean again.  
      The requirements of the fuel system determine the size of the filter. The component packaging determines the maximum diameter of the filter. However, the velocity of the fluid passing through the filter is critical for washing the contaminants from the filter. Velocity of the fluid is controlled by the diameter of the individual tubes within the filter.  
      The surface area of the sidewalls of the tubes governs the amount of filtration obtained by the filter as a whole. Because the component packaging is somewhat fixed the use of additional tubes provides benefits in design freedom. By adding additional tubes to the filter additional surface area of sidewalls is obtained without requiring undesirable lengthening of the filter and increased contaminant capacity when operated in barrier mode. The tubes may have a constant diameter cross-section. Alternatively, the cross-section may be reduced in diameter over the length of the tubes, such that the fluid velocity within the tubes remains relatively constant relative to the draw of radial washed fluid.  
      The use of multiple wash tubes allows for increased filter surface area, which allows greater contaminant capacity with minimal pressure drop, during barrier mode operation, allows for optimum filter tube sizing to obtain ideal wash velocities which ensures effective cleaning of the filter element and a more compact filter package for the given screen area, allowing for less weight than conventional packaging. 
    
    
      These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.  
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is side view of a wash flow filter and bore assembly of the present invention;  
       FIG. 2  is a schematic illustration of fluid flow through a fuel filtering system;  
       FIG. 3  is an illustration of fluid flow through a portion of the wash flow filter of the present invention;  
       FIG. 4  is a perspective view of one embodiment of a wash flow filter of the present invention; and  
       FIG. 5  is an illustration of a conical filter tube of a wash flow filter of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       FIG. 1  illustrates a fuel system  10  when in a conventional wash mode having a filter assembly  12  that includes a wash flow filter  14 . A bore  16  is located in a wall  18  for receiving the filter  14 . The filter  14  includes a first header  20  and a second header  22 . Multiple tubes  24  run from the first header  20  to the second header  22 . The tubes  24  are formed of a material that will block contaminants, i.e. a mesh or screen material. A first seal  26  is located in the first header  20  to prevent fluid outside the bore  16  and within the tubes  24  from mixing with fluid inside the bore  16  and outside the tubes  24 . The second header  22  has a second seal  28  similar to the first seal  26 . The second seal  28  prevents fluid outside the bore  16  and within the tubes  24  from mixing with fluid within the bore  16 .  
       FIG. 2  is a schematic illustrating fluid flow through the fuel system  10  when in the conventional wash mode. Fuel from a storage tank  32  enters the filter assembly  12 , through an inlet  33 . The fluid passes into tubes  24 . A portion of the fluid exits the tubes  24  into the bore  16 . Fluid within the bore  16  and outside the tubes  24  is carried away by passages  30  to use for combustion within an engine  34 . In particular, engine  34  may be an aircraft engine. The rest of the fluid passes straight through the tubes  24  out a second end of the filter  14  to an outlet return  35 . This fluid returns to the storage tank  32  to be later passed through the filter  14  again.  
       FIG. 3  shows a portion of the wash flow filter  14  when in the conventional wash mode showing a single tube  24 . Fluid enters the filter  14  at a first end  36  and exits the filter  14  at a second end  38 . Fluid flow is indicated by arrow F. Thus, as flow passes through the tubes  24  some of the fluid exits radially through sidewalls  40  of the tubes  24 . The sidewalls  40  filter particles out of the fluid as the fluid passes through the sidewalls  40  to obtain a filtered fluid. Arrows R indicate the radial fluid flow through the sidewalls  40 . As fluid flows along the fluid path F the particles blocked by the sidewalls  40  are washed out the second end  38  of the tube  24 . Thus, the filter  14  is self-cleaning. The washed fluid that has exited the tubes  24  is carried away by passages  30  in the bore  16  to an engine  34 .  
      The fuel filter assembly  12  has two distinct operating modes a conventional wash flow mode and a barrier filter mode. In one embodiment of a fuel system  10 , the axial motive flow through the filter  14  is periodically shut off forcing all flow to pass through the tube  24  radially, indicated by arrows R. The fluid path F is closed off at the second end  38  to prevent fluid from exiting filter  14  into the outlet return  35  and passing back to the storage tank  32 . This puts the screen into a pure “barrier” mode. During this time period, the screen collects all the contaminant that is larger than the minimum screen opening and proceeds to become clogged until the axial motive flow is re-instated allowing the wash mode to be re-established. That is the fluid path F at the second end  38  is opened. Within a short period of time the screen is washed fully clean again.  
       FIG. 4  shows a perspective view of the wash flow filter  14 . The requirements of the fuel system determine the filtration level and amount of filtration area required by the filter  14 . The diameter and length of the bore  16  determines the maximum envelope of the filter  14 . However, the velocity of the fluid passing through the filter  14  is critical for washing the contaminants from the fluid. Velocity of the fluid is controlled by the diameter D of the each tube  24 . Therefore, one skilled in sizing of filtration systems can iterate between the number and size of filtration tubes  24  that can fit within the maximum envelope and length of the bore  16 , to achieve the desired wash velocity and filtration area.  
      The surface area of the sidewalls  40  governs the amount of filtration obtained by the filter  14  and its contaminant holding capacity in barrier mode. In order to decrease the pressure drop during barrier mode and increase the contaminant holding capacity, additional tubes may be utilized within the filter assembly. By adding additional tubes  24  to the filter  14  additional surface area of sidewalls  40  is obtained without requiring undesirable lengthening of the filter  14 . Also, the plurality of tubes keeps their diameter small and helps to maintain the desirable high fluid velocity during wash mode. Although, in the embodiment shown, there are four tubes  24 , one skilled in the art would realize the number of tubes may vary for each application. The tubes  24  shown have a constant diameter cross-section. Referring to  FIG. 5 , the cross-section of the tubes  24  may also be reduced in diameter over the length L. Thus, as fluid exits the tubes  24 , the fluid velocity within the tubes  24  remains constant.  
      The filter  14  is assembled by placing the first end  36  of the tubes  24  into the first header  20  and the second end of the tubes  24  into the second header  22 . The first header  20  and the second header  22  are manufactured to have the one hole  42  for each required tube  24 . Alternatively, the first end  36  of each tube  24  could be inserted into the first header  20  and then the second end  38  of each tube  24  could be inserted into the second header  22  until all the holes within the first header  20  and the second header  24  have a corresponding tube  24 .  
      Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.