Abstract:
A filter element that is provided with automatic air bleeding features to efficiently bleed air from a fuel filter module containing the filter element. The filter element has an upper end cap with one or two air vents. One of the vents provides a bypass for air through wet filter media through which air from the fuel supply may not be able to pass through easily. The inner air vent is located on the inside of a circle formed by attachment clips that attach the respective filter element to a removable cover. The inner air vent allows for air inside the filter module to be easily purged out via a drain hole on the fuel filter module, while providing resistance to fuel. The drain hole is provided on the filter module which is internally connected to the fuel outlet and therefore to the fuel tank.

Description:
FIELD 
     This disclosure relates to a filter element, in particular a fuel filter element, configured with automatic air bleeding features. 
     BACKGROUND 
     For heavy-duty diesel engines where achieving maximum fuel pressure is desired, any trapped air within large fuel housings can pose a great engineering challenge. Air can become trapped within the fuel housing in a number of ways, including as a result of a new filter element being installed in the housing and air entrained in fuel entering the fuel filter housing. 
     Manual external or internal air-bleed valves have been developed to purge air outside of the filter housing. Various automatic air bleeding fuel filter designs are also known. The use of external air-bleed valves can present additional possibilities of functional failure where fuel-leaks could occur. Moreover, to manually bleed air out, some amount of fuel can spill out of the housing posing safety risks to the operator. The same safety risks apply to draining the fuel manually out of the housing during filter replacement. 
     In addition, fuel supply to a high pressure fuel pump typically utilizes part of the returned fuel from an in-built reservoir of the fuel filter housing which could contain air that&#39;s already vented out from the fuel filter housing. Some of this air can make it back into the Stage-1 filter through the standpipe which is on the upstream or dirty side of the filter media. If the media air-vent is located on the downstream or “clean-side” of the filter media, then the air-vent functionality will be reduced or eliminated altogether and air from the fuel supply could cause engine performance issues if it does not get vented out. 
     SUMMARY 
     A filter element is described that is provided with automatic air bleeding features to efficiently bleed air from a filter housing containing the filter element. The described filter element and filter housing requires no manual air-bleeding from the fuel module during its service. To facilitate the description, the filter element will be specifically described as being a fuel filter element. However, the concepts described herein are applicable to any type of filter element/filter housing application where air needs to be bled from the filter housing. 
     Both stage-1 and stage-2 fuel filters will be described herein. The stage-1 filter element is described as having a first or upper end cap with two air vents, an inner air vent and a media air vent. The media air vent provides a bypass for air through wet filter media through which air from the fuel supply may not be able to pass through easily. The inner air vent is provided on both the stage-1 and the stage-2 fuel filters. In each case, the inner air vent is located on the inside of a circle formed by attachment clips that attach the respective filter element to a removable receptacle cover. The inner air vent allows for air inside the filter housing to be easily purged out via a drain hole on the fuel filter housing, while providing resistance to fuel. The drain hole is provided on the filter housing which is internally connected to the fuel outlet and therefore to the fuel tank. The removable filter element therefore needs to provide a hermetic passage from the upper end cap, through a center tube of the filter element, and through a bottom end cap. 
     In one embodiment, the stage-1 fuel filter can also use locating features to help locate the media air vent on the upstream or dirty side of the filter media. In particular, the center tube of the stage 1 filter element includes a pleat separation element, for example a wedge-shaped feature, that helps to separate two adjacent pleats between which the media air vent will be located. In addition, the center tube will include an alignment element that interacts with a corresponding alignment element on the upper end cap to help appropriately locate the media air vent on the upstream or dirty side of the filter element between the two adjacent pleats. 
     In one example, a filter element comprises a ring of filtration media having a first end and a second end and circumscribing a central cavity. A first end cap is sealingly attached to the first end of the filtration media, with the first end cap including a vent passageway. In addition, a second end cap is sealingly attached to the second end of the filtration media, with the second end cap including a plurality of vent openings extending therethrough. A center tube is disposed within the central cavity, with the center tube having a first end connected to the first end cap and a second end connected to the second end cap. The center tube further includes a fuel passageway and an air vent passageway, with the air vent passageway being fluidly separated from the fuel passageway and the air vent passageway being in fluid communication with the vent passage in the first end cap and with the vent openings in the second end cap. Also, first and second seals are attached to the second end cap, with the first seal being located radially inward of the second seal, the first seal being disposed within an opening formed in the second end cap, the second seal being disposed in a second opening formed by the second end cap, and the vent openings in the second end cap being between the first seal and the second seal. 
     When the filtration media is pleated, the filtration media has an unfiltered fluid side and a filtered fluid side, and the first end cap further includes a media vent passage radially outward from the vent passage. The media vent passage is disposed on the unfiltered side of the media between two of the pleats. To facilitate proper positioning of the vent passage, a pleat separation element can be formed on the center tube adjacent to the first end thereof and adjacent to the media vent passage on the first end cap, with the pleat separation element being disposed between the two pleats. The pleat separation element helps to separate the two pleats so that the media vent passage is properly located on the dirty or unfiltered fluid side of the filtration media between the two pleats. 
     In addition, an alignment element can be provided at the first end of the center tube that is engaged with a corresponding alignment element on the first end cap. The alignment elements help to ensure proper orientation of the center tube, to help properly position the pleat separation element relative to the media vent passage. 
     The filter element can include other elements as well, such as an outer coalescing element surrounding the filtration media. The outer coalescing element has a first end connected to the first end cap and a second end connected to the second end cap. 
    
    
     
       DRAWINGS 
         FIG. 1  illustrates a fuel filter described herein removably installed within a respective receptacle in a fuel filter module. 
         FIG. 2  is a cross-sectional view of the fuel filter element of  FIG. 1 . 
         FIG. 3  is an exploded view of the components of the fuel filter element of  FIG. 1 . 
         FIG. 4  is a detailed view illustrating the air bleed path near the base of the fuel filter. 
         FIG. 5  is a partially exploded view of the fuel filter element illustrating a pleat spacer on the center tube of the fuel filter element. 
         FIG. 6  is a side view of the center tube of the fuel filter element of  FIG. 5 . 
         FIG. 7  is an end view of the center tube of the fuel filter element of  FIG. 5  illustrating alignment features on the end of the center tube. 
         FIG. 8  is a close-up view of the engagement between the center tube and the upper end plate of the fuel filter element of  FIG. 5 . 
         FIG. 9  illustrates another embodiment of a fuel filter element described herein removably installed within a respective receptacle in the fuel filter module. 
         FIG. 10  is a cross-sectional view of the fuel filter element of  FIG. 9 . 
         FIG. 11  is an exploded view of the components of the fuel filter element of  FIG. 9 . 
         FIG. 12  is a view similar to  FIG. 9  but showing partial removal of the fuel filter element from its receptacle in the fuel filter module. 
         FIG. 13  is a cross-sectional view of another embodiment of a stage 1 fuel filter element disposed on a standpipe. 
         FIG. 14  is a cross-sectional view of the fuel filter element in  FIG. 13 . 
         FIG. 15  is a view of the upper end of the center tube of the fuel filter element of  FIG. 13 . 
         FIG. 16  illustrates an alignment feature and vent passageway formed in the upper end cap of the fuel filter element of  FIG. 13 . 
         FIG. 17  illustrates the venting of air from the filtration media through the end cap of the fuel filter element of  FIG. 13 . 
         FIG. 18  illustrates the flow of vented air through the base end of the fuel filter element of  FIG. 13 . 
         FIG. 19  illustrates another embodiment similar to  FIG. 18 . 
         FIG. 20  is a cross-sectional view of another embodiment of a stage 2 fuel filter element disposed on a standpipe. 
         FIG. 21  is a cross-sectional view of the fuel filter element of  FIG. 20 . 
     
    
    
     DESCRIPTION 
       FIGS. 1-8  illustrate a stage 1 fuel filter assembly  10  that includes a fuel filter element  12  removably installed within a receptacle  14  of a fuel filter module. A stage 2 fuel filter assembly  200  is illustrated in  FIGS. 9-12 . The stage 1 filter element  12  is an inside-out flowing filter, while a stage 2 filter element  208 , discussed further below, is an outside-in flowing filter. The stage 1 filter element  12  and the stage 2 filter element  208  are mounted within respective receptacles of a filter module in a side-by-side relationship and work in series. The receptacles for the filter elements are in communication with one another and effectively form a single larger cavity. 
     In operation, fuel that is filtered by the stage 1 filter element  12  flows from the receptacle for the stage 1 filter element into the receptacle for the stage 2 filter element  208 . Fuel exiting out a lift pump (for example, a gear pump) has finely dispersed water droplets that the stage 1 filter&#39;s media material coalesces from smaller droplets into bigger drops which finally sink to the lower-most portion of the filter module. The stage 2 filter media removes finer hard particles. The stage 2 filter also strips out water droplets that make it through from the stage 1 filter. Filtered fuel exiting out of the stage 2 filter is then routed to a high pressure pump. 
     With reference to  FIG. 1 , the receptacle  14  includes a fixed housing  16  and a removable cover  18  that is removably attached to the fixed housing, for example using threads. In use, the cover  18  is attached to the fixed housing  16  so that the two define an interior volume sufficient to receive the fuel filter element  12 . The cover  18  is sealed with the fixed housing  16  to prevent fuel leaks from the interior thereof. The cover  18  can be removed from the fixed housing to access the interior volume for removal of the filter element. 
     As shown in  FIGS. 1 and 4 , the fixed housing  16  includes a base end  20  and a standpipe  22  extends upwardly from the base end  20  into the interior of the fixed housing. In this embodiment, the standpipe  22  forms an inlet for fuel to be introduced into the fuel filter assembly  10 . The base  20  also includes a drain hole(s)  24  that is in fluid communication with the fuel tank or other fuel storage location through which air and/or fuel mixed with air is returned to the fuel tank after being vented from the fuel filter. 
     The cover  18  also includes attachment structure  26  defined on the interior thereof that detachably engages with corresponding structure formed at the upper end of the filter element  12  so that when the cover  18  is removed, the filter element  12  is removed with the cover  18 . The filter element  12  can then be removed from the cover for replacement. Attachment structures between a removable cover and a filter element for removing the filter element when the cover is removed are known in the art. 
     Turning now to the filter element  12 , the filter element is designed to filter the incoming fuel entering through the standpipe  22  prior to the fuel flowing to the stage 2 filter  200 . In the illustrated embodiment, the filter element is designed for inside-out flow with the fuel entering through the standpipe  22 , flowing generally radially outward through the filter element which filters the fuel, and then flowing to and through the stage 2 filter element before exiting out through a fuel outlet. 
     With reference to  FIGS. 1-3 , the filter element  12  includes a ring of filtration media  30 , a first or upper end cap  32 , a second or lower end cap  34 , and a center tube  76 . The filtration media  30  has a first or upper end  40  and a second or lower end  42  and circumscribes a central cavity  44 . In the illustrated embodiment, the filtration media  30  is pleated and is generally cylindrical in construction, although other forms and shapes of filtration media can be used. 
     The first end cap  32  is sealingly attached to the first end  40  of the filtration media using any suitable attachment method, for example using an adhesive or embedding the end  40  into the end cap  32  which can be made of plastic or metal. The first end cap  32  is a closed end cap in that fuel is not intended to flow through the end cap  32 . However, as described further below, the end cap  32  includes an air vent passageway  46  and a media air vent  48  which permit venting of air through the end cap  32 . 
     As best seen in  FIGS. 2 and 3 , the end cap  32  includes a plate section  50  that is attached to the first end  40  of the filtration media  30 . The plate section  50  surrounds a skirt  52  that includes a portion  54  extending downwardly into the central cavity  44  and a portion  56  that extends upwardly. A plate  58  extends across the skirt portion  56  to close the skirt  52 . A plurality of resilient fingers  60  extend upwardly from the plate  58  for engagement with the attachment structure  26  on the cover  18  to connect the filter element  12  to the cover  18 . 
     As shown in  FIG. 2 , the air vent passageway  46  is formed in and extends through the plate  58 . This provides fluid communication between the upper end of the interior of the fuel filter assembly  10  and the central cavity  44  so that air from the upper end of the fuel filter can vent into the central cavity  44 . 
     In addition, the media air vent  48  is formed in the plate section  50  so that it is located radially outward from the air vent passageway  46 . As will be discussed further below, the media air vent  48  is disposed on the unfiltered side of the filtration media  30  between two of the pleats. 
     The second end cap  34  is sealingly attached to the second end  42  of the filtration media using any suitable attachment method, for example using an adhesive or embedding the end  42  into the end cap  34  which can be made of plastic or metal. 
     With reference to  FIGS. 2-4 , the second end cap  34  includes a plate section  62  that is attached to the second end  42  of the filtration media  30 . The plate section  62  surrounds a skirt  64  that includes a portion  66  extending downwardly and a portion  68  that extends upwardly. A circumferential wall  70  extends radially inwardly from the skirt  64 , and a second skirt portion  72  extends upwardly from the inner edge of the circumferential wall  70  spaced from and substantially parallel to the skirt portion  68 . As best seen in  FIG. 4 , a plurality of vent openings  74  are formed in and extend through the wall  70  to place the space between the skirt portions  68 ,  72  in fluid communication with the opposite side of the end cap  34 . 
     Returning to  FIGS. 2 and 3 , a center tube  76  is disposed within the central cavity  44 . The center tube  76  has a first end  78  sealingly connected to the first end cap  32  and a second end  80  sealingly connected to the second end cap  34 . In particular, the first end  78  is attached to the skirt portion  54  of the end cap  32  and the second end  80  is attached to the skirt portion  68  (see  FIG. 4 ). The attachment between the end  78  and the skirt portion  54 , and between the end  80  and the skirt portion  68 , can be accomplished in any suitable manner so long as fluid leakage between the surfaces is prevented, for example a friction fit, using adhesive, welding or combinations thereof. 
     The center tube  76  further includes a fuel passageway  82  and one or more air vent passageways  84 . The passageways  82 ,  84  are defined by a wall  86  within the center tube  76  that defines an opening  87  that extends from one side of the center tube to the other for fuel to be filtered to enter into the central cavity  44  of the filter media  30 . At the base of the wall  86  a cylindrical tube  88  is formed through which the standpipe  22  can extend as shown in  FIG. 4 . 
     As best seen in  FIG. 4 , a first cylindrical gasket  90  is disposed between the tube  88  and the skirt portion  72  to seal between the tube  88  and the skirt portion  72 . The gasket  90  also includes a cylindrical portion  92  that projects radially inward beyond the tube  88  for sealing with the outer surface of the standpipe  22 . The base of the gasket  90  is supported by a small rib  94  that projects radially inwardly from the skirt portion  72 . 
     A second cylindrical gasket  96  is attached to the inner surface of the skirt portion  66  for sealing between the second end cap  34  and the base end  20  of the fixed housing  16  when the filter element is installed. 
     The first and second gaskets  90 ,  96  can be secured in any suitable manner, for example using snap features, using an adhesive, or being overmolded onto the respective skirt portions. 
     Returning to  FIGS. 2 and 3 , the filter element  12  can also include a coalescing element  98  surrounding the filtration media  30  and an outer support wrap  100 . The coalescing element  98  is designed to coalesce water from the fuel. The outer coalescing element  98  has a first end connected to the plate section  50  of the first end cap  32  and a second end connected to the plate section  62  of the second end cap  34 . However, use of the coalescing element is optional. The support wrap  100  helps to support the filtration media  30  and, if present, the coalescing element  98 . 
     As indicated above, the media air vent  48  is disposed on the unfiltered side of the filtration media  30  between two of the pleats. With reference to  FIGS. 5-8 , to facilitate proper positioning of the media air vent  48 , a pleat separation element  102  is formed on the outer surface of the center tube  76  adjacent to the first end  78  thereof. When the center tube  76  is assembled into the filter element, the pleat separation element  102  is also adjacent to the media air vent  48  on the first end cap  32  as best seen in  FIG. 8 . 
     As best seen in  FIG. 6 , the pleat separation element  102  is a wedge-shaped element that projects from the outer surface of the center tube. As the center tube  76  is being installed into the filtration media  30 , the pleat separation element  102  fits between two adjacent pleats and separates those two pleats to create a larger space between the two pleats so that the media air vent  48  can more easily be positioned between the two pleats on the unfiltered or dirty side thereof. 
     In addition, alignment elements  104   a ,  104   b  are formed at the first end  78  of the center tube  76  and corresponding alignment elements  106  are formed on the skirt portion  54 . The alignment elements  104   a ,  104   b ,  106  help to ensure proper orientation of the center tube  76 , to help properly position the pleat separation element  102  relative to the media air vent  48 . In the illustrated embodiment, the alignment elements  104   a ,  104   b  comprise radially outward protruding channels formed on diametrically opposite sides of the center tube  76 , and the alignment elements  106  comprise correspondingly shaped protrusions formed on the skirt portion  54  that fit into the channels. As shown in  FIG. 7 , the alignment elements  104   a ,  104   b  are of different size with the alignment element  104   a  being larger than the alignment element  104   b . The alignment elements  106  would also have corresponding different sizes. Therefore, the center tube  76  can only be attached to the skirt portion  54  in the correct orientation. 
     Operation of the fuel filter assembly  10  will now be described with reference to  FIG. 1 . Unwanted air can enter the receptacle  14  as a result of a new filter element  12  being installed and/or as a result of air entrained in fuel entering through the standpipe  22 . During operation, fuel to be filtered enters via the standpipe  22 , into the fuel passageway  82 , and through opening  87  into the central cavity of the filtration media. The fuel then flows radially outward through the filtration media which filters the fuel. If the coalescing element is present, the fuel flows through the coalescing element, and then passes through the stage 2 filter element  208 . Coalesced water drops sink to the lower most portion of the module where it can be drained through a suitable drain. 
     Air inside the housing  14  is shown by the diagrammatic bubbles in  FIG. 1 . Air between the outer side of the filtration element and the inside of the filter housing and air at the upper end of the filter housing can vent through the air vent passageway  46  to the interior of the center tube  76 . Any air that enters through the standpipe and becomes trapped on the dirty side of the filtration media within the central cavity  44  can vent to the upper end of filter housing through the media air vent  48  and then vent through the air vent  46  into the interior of the center tube. Once in the center tube, the air flows down to the base of the filter element and through the vent opening(s)  74  and from there through the drain hole  24  back to the fuel tank. 
     With reference to  FIGS. 9-12 , the stage 2 fuel filter assembly  200  will now be described. The fuel filter assembly  200  is somewhat similar in construction to the fuel filter assembly  10 , with one of the biggest differences being that the fuel filter element of the filter assembly  200  does not include a media air vent and has a different flow direction. 
     With reference to  FIG. 9 , the fuel filter assembly  200  includes a receptacle  202  having a fixed housing  204  and a removable receptacle cover  206  that is removably attached to the fixed housing, for example using threads. In use, the cover  206  is attached to the fixed housing  204  so that the two define an interior volume sufficient to receive the fuel filter element  208 . The interior of the receptacle  202  is in fluid communication with the receptacle of the stage 1 filter so that fuel that has been filtered by the stage 1 filter flows into the receptacle  202  for filtration by the fuel filter element  208 . The cover  206  is sealed with the fixed housing  204  to prevent fuel leaks from the interior thereof. The cover  206  can be removed from the fixed housing to access the interior volume for removal of the filter element. 
     As shown in  FIGS. 9 and 12 , the fixed housing  204  includes a base end and a standpipe  210  extends upwardly from the base end into the interior of the fixed housing. In this embodiment, the standpipe  210  forms an outlet for fuel that has been filtered by the fuel filter element  208 . The base also includes a drain hole(s)  212  that is in fluid communication with the fuel tank or other fuel storage location through which air and/or fuel mixed with air is returned to the fuel tank after being vented from the fuel filter. Fuel can also drain through the drain hole(s)  212  back to the fuel tank when the filter element  208  is lifted upward so that the fuel filter assembly  200  can auto-drain during filter element changes. 
     Similar to the filter assembly  10 , the cover  206  also includes attachment structure defined on the interior thereof that detachably engages with corresponding structure formed at the upper end of the filter element  208  so that when the cover  206  is removed, the filter element  208  is removed with the cover. The filter element can then be removed from the cover for replacement. Attachment structures between a removable cover and a filter element for removing the filter element when the cover is removed are known in the art. 
     Turning now to the filter element  208 , the filter element is designed to filter the fuel already filtered by the stage 1 filter element prior to the fuel exiting the fuel module through the standpipe  210 . Thus, in the illustrated embodiment, the filter element  208  is designed for outside-in flow with the fuel flowing generally radially inwardly through the filter element which filters the fuel, enters the standpipe  210  through suitable openings, and then flowing out through the standpipe  210 . 
     With reference to  FIGS. 9-11 , the filter element  208  includes a ring of filtration media  214 , a first or upper end cap  216 , a second or lower end cap  218 , and a center tube  220 . The filtration media  214  has a first or upper end  222  and a second or lower end  224  and circumscribes a central cavity  226 . In the illustrated embodiment, the filtration media  214  is pleated and is generally cylindrical in construction, although other forms and shapes of filtration media can be used. 
     The first end cap  216  is sealingly attached to the first end  222  of the filtration media using any suitable attachment method, for example using an adhesive or embedding the end  222  into the end cap  216  which can be made of plastic or metal. The first end cap  216  is a closed end cap in that fuel is not intended to flow through the end cap. However, as described further below, the end cap  216  includes an air vent passageway  226 , similar to the air vent passageway  46  of the filter element  12 , which permits venting of air through the end cap. 
     As best seen in  FIGS. 10 and 11 , the end cap  216  includes a plate section  230  that is attached to the first end  222  of the filtration media  214 . The plate section  230  surrounds a skirt portion  232  that extends downwardly into the central cavity  226 . A plate  234  extends across the skirt portion  232  from the inner end of the plate section  230  to close the skirt portion. As with the filter element  12 , a plurality of resilient fingers extend upwardly from the end cap  216  for engagement with the attachment structure on the cover  206  to connect the filter element to the cover. 
     As shown in  FIG. 10 , the air vent passageway  226  is formed in and extends through the plate  234 . This provides fluid communication between the upper end of the interior of the fuel filter assembly  200  and the central cavity  226  so that air from the upper end of the fuel filter can vent into the central cavity  226 . 
     The second end cap  218  is sealingly attached to the second end  224  of the filtration media using any suitable attachment method, for example using an adhesive or embedding the end  224  into the end cap  218  which can be made of plastic or metal. 
     With reference to  FIGS. 10-12 , the second end cap  218  includes a plate section  240  that is attached to the second end  224  of the filtration media  214 . The plate section  240  surrounds a skirt portion  242  extending downwardly. A circumferential wall  244  interconnects the plate section  240  and the skirt portion  242 , and a skirt portion  246  extends upwardly from the inner edge of the circumferential wall  244 . The skirt portion  246  has a sufficient radial thickness in which a plurality of axially extending vent openings  248  are formed that extend through the skirt portion to place the upper side of the skirt portion  246  in fluid communication with the opposite side of the end cap  218 . 
     Returning to  FIGS. 10 and 11 , the center tube  220  is disposed within the central cavity  226 . The center tube  220  has a first end  250  sealingly connected to the first end cap  216  and a second end  252  sealingly connected to the second end cap  218 . In particular, the first end  250  is attached to the skirt portion  232  of the end cap  216  and the second end  252  is attached to the skirt portion  246  (see  FIG. 10 ). The attachment between the end  250  and the skirt portion  232 , and between the end  252  and the skirt portion  246 , can be accomplished in any suitable manner so long as fluid leakage between the surfaces is prevented, for example a friction fit, using adhesive, welding or combinations thereof. 
     The center tube  220  further includes a fuel outlet passageway  254  and one or more air vent passageways  256 . The passageways  254 ,  256  are defined by a wall  258  within the center tube  220  that defines an opening  260  that extends from one side of the center tube to the other for fuel that has been filtered to enter into the standpipe  210 . At the base of the wall  258  a cylindrical tube  262  is formed through which the standpipe  210  can extend as shown in  FIGS. 9 and 12 . 
     As best seen in  FIG. 10 , a first cylindrical gasket  264  is disposed between the tube  262  and the skirt portion  246  to seal between the tube and the skirt portion. The gasket  264  also includes a cylindrical portion  266  that projects radially inward beyond the tube  262  for sealing with the outer surface of the standpipe  210 . 
     A second cylindrical gasket  268  is attached to the inner surface of the skirt portion  242  for sealing between the second end cap  218  and the base end of the fixed housing  204  when the filter element is installed. 
     The first and second gaskets  264 ,  268  can be secured in any suitable manner, for example using snap features, using an adhesive, or being overmolded onto the respective skirt portions. 
     Returning to  FIGS. 10 and 11 , the filter element  208  can also include a hydrophobic screen  270  surrounding the filtration media  214 . The screen  270  is designed to remove water from the fuel. The screen  270  has a first end connected to the plate section  230  of the first end cap  216  and a second end connected to the plate section  240  of the second end cap  218 . However, use of the hydrophobic screen  270  is optional. 
     Operation of the fuel filter  200  will now be described with reference to  FIGS. 9 and 12 . During operation, fuel from the stage 1 filter enters into the receptacle  202 , flows radially inwardly through the filtration media which filters the fuel. After being filtered, the fuel flows into the opening  260  in the center tube  220  and into a suitable opening(s) in the standpipe  210 , and then out through the standpipe. 
     Air inside the receptacle  202  is shown by the diagrammatic bubbles in  FIG. 9 . Air between the outer side of the filtration element and the inside of the receptacle and air at the upper end of the filter housing can vent through the air vent passageway  226  to the interior of the center tube  220 . Once in the center tube, the air flows down to the base of the filter element and through the vent opening(s)  248  and from there through the drain hole(s)  212  back to the fuel tank. 
     In addition, as illustrated in  FIG. 12 , upon removal of the cover  206 , the filter element  208  also gets lifted up. When the filter element is lifted up, the filter element is unseated from base of the fixed housing  204 , thereby exposing the drain hole(s)  212 . Any fuel remaining in the housing  204  can drain through the drain hole(s)  212  and back to the fuel tank. 
     With reference to  FIGS. 13-18 , another embodiment of a stage 1 fuel filter element  300  is illustrated that is configured for inside-out fuel flow. The fuel filter element  300  includes a center tube  302  that is generally cage-like in construction, but which includes an air vent passageway  304  that extends from a first solid end section  306  to a second solid end section  308 . The end section  306  seals with a skirt portion  310  formed on an upper end cap  312 , while the end section  308  seals with a skirt portion  314  formed on a lower end cap  316 . The upper end cap  312  is formed with an air vent passageway  318  which allows vent air to enter into the space  320  defined by the skirt portion  310 , the solid end section  306 , the end cap  312 , and a plate  322  that closes off the upper end of the center tube  302 . The air can then flow into the passageway  304  and down towards the base of the filter element  300 . 
     In addition, the solid end section  306  and the skirt portion  310  are configured to allow air to vent from the dirty side of the filtration media and through the solid end section  306  and the skirt portion  310  into the space  320  as shown by the arrows in  FIGS. 13 and 17 . With reference to  FIGS. 15 and 16 , the solid end section  306  of the center tube  302  includes a pair of opposing slots  324  formed therethrough. The skirt portion  310  includes a pair of opposing small grooves  326  (only one groove is visible in  FIG. 16 ) that extend through the skirt portion and that when properly assembled are positioned adjacent to the slots  324 . The skirt portion  310  also includes a pair of keys  328  that fit into the slots  324  for properly orienting the center tube  302 . 
     As shown in  FIG. 17 , air that is introduced into the fuel filter module via fuel entering the standpipe  330  collects on the dirty side of the filtration media. The air is able to vent through the slots  324  and then through the grooves  326  into the space  320  where the air can then enter the air vent passageway  304  for venting from the filter module. 
     With reference to  FIGS. 13-14  and  18 , the base of the filter element  300  will now be described. A gasket  332  is installed on an inside of the center tube  302 . A first plurality of tabs  334  project radially inwardly from the upper end of the skirt portion  314 , while a second plurality of tabs  336  project radially inwardly from a lower end of the skirt portion. The lower end of the gasket  332  can be supported by or spaced from the tabs  334 . A second gasket  338  is disposed between the tabs  334  and the tabs  336  for sealing with the base of the fuel filter module. 
     As shown in  FIGS. 13 and 18 , fuel to be filtered enters via the standpipe  330 . The fuel then flows radially outwardly through the filtration media which filters the fuel. After being filtered, the fuel then flows to the stage 2 filter. Optionally, a coalescing element  340  can be provided around the filtration media for coalescing water in the fuel. 
     Air within the filter housing can vent from the module via the air vent passageway  318  into the space  320  and through the passageway  304 . Likewise, air on the dirty side of the filtration media can vent through the slots  324 , through the channels  326 , into the space  320  and through the passageway  304 . The air in the passageway  304  flows to the base of the filter element where it exits the passageway  304 , flows through gaps between the tabs  334  and into a drain  342  (see  FIG. 13 ) in the base of the module which can be fluidly connected to the fuel tank. 
       FIG. 19  illustrates an embodiment that is similar to  FIG. 18 , but instead of the first set of tabs  334 , a continuous flange  350  is provided with a plurality of holes  352  formed in the flange  350  to allow air to vent through the flange  350  and into the drain  342 . 
     With reference to  FIGS. 20-21 , another embodiment of a stage 2 fuel filter element  400  is illustrated that is configured for outside-in fuel flow. The fuel filter element  400  is similar in construction to the fuel filter element  300  including the center tube  302 , vent air passageway  304 , the air vent passageway  318  in the upper end cap, and the like. Since the fuel filter element  400  is similar in construction to the fuel filter element  300 , the fuel filter element  400  need not be described in detail. However, the fuel filter element  400  does not include the slots and grooves to allow air to vent from the dirty side of the filtration media and through the solid end section  306  and the skirt portion  310  into the space  320 . 
     As shown in  FIG. 20 , fuel to be filtered enters through an inlet. The fuel then flows radially inwardly through the filtration media which filters the fuel. After being filtered, the fuel then flows into one or more openings in a standpipe  402  and out of the module. 
     Air within the module can vent from the module via the air vent passageway  318  into the space  320  and through the passageway  304 . The air in the passageway  304  flows to the base of the filter element where it exits the passageway  304 , flow through gaps between the tabs  334  and into a drain  342  in the base of the housing which can be fluidly connected to the fuel tank. 
     Although the upper end cap has been described as having a single air vent passageway, such as the passageway  46 , more than one air vent passageway can be provided in any of the described embodiments. Likewise, although a single media air vent has been described, more than one media air vent can be provided in any of the described embodiments. 
     The invention may be embodied in other forms without departing from the spirit or novel characteristics thereof. The embodiments disclosed in this application are to be considered in all respects as illustrative and not limitative. The scope of the invention is indicated by the appended claims rather than by the foregoing description; and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.