Abstract:
A secondary filter cartridge radially nested within and radially supported by a main filter cartridge. The secondary cartridge has a flexible multi-leg crown “with slits” which engage a receptacle of the main filter element for radial support and a central pin projection interior to the crown extending outwards to protect the crown from impact damage. The main filter cartridge bottom end disk has axially extending, spaced apart projections engaged into matching pockets or gaps provided between engaging inward projections on an interior end face of the filter housing, rotationally fixing or locking the filter housing and the main filter cartridge. The main filter cartridge includes an anti-rotation housing engagement member extending through a filter housing wall to the exterior indicating presence of a properly installed filter cartridge and rotatably locking position of the housing and main filter cartridge.

Description:
TECHNICAL FIELD 
     The present invention is related to air filter cartridges and an air filter system for filtering air delivered to internal combustion engines, compressors or other apparatus requiring filtered air. The system includes a main filter cartridge and optionally a secondary filter cartridge radially nested within the main filter cartridge, the main and secondary cartridges cooperatively engaging with each other and with interior features of the filter housing. 
     BACKGROUND OF THE INVENTION 
     Various types of air filter cartridges and air filter systems for filtering particulates and contaminants from air for internal combustion engines and compressors are known in the art. 
     Known are varieties of elongated cylindrical cartridge filter elements having an open central interior and are configured to filter a radially directed airflow. Such filter elements are typically removeably installed into complimentary configured filter housings. 
     Varieties of filter housings having removable covers or detachable housing portions and configured to receive such filter elements are also known in the art. Such devices find application in filtering various liquid and gaseous fluid media. 
     As is generally known in the art, internal combustion engines such as stationary engines, motor vehicles and off road equipment require the air filtration systems to remove particulate and possibly chemical contaminations from the intake air. The air filter system typically includes an openable/serviceable filter housing having air intake and outlet ports as well as a filter element or filter cartridge removeably and replaceably installed with the filter housing. 
     SUMMARY OF THE INVENTION 
     In various aspects of the invention a filter cartridge assembly and system includes a secondary filter cartridge radially nested within and radially supported by a main filter cartridge. The secondary cartridge has a flexible multi-leg crown “with slits” which engages into a receptacle in an outwardly extending dome in the bottom end disk of the main filter element for radial support and includes a central pin projection interior to the crown with a long outwardly extending length than the crown and is structurally more robust than the crown, extending beyond the crown to protect the crown from impact damage (for example if the crown filter cartridge is dropped or mishandled). The main filter cartridge bottom end disk also has a plurality of axially extending, spaced apart elastomeric projections configured to engaged into complimentary configured pockets or gaps provided between other inward projections provided on an interior end face of the filter housing, thereby rotationally fixing or locking the filter housing and the main filter cartridge. The main filter cartridge includes an anti-rotation housing engagement member or pin which extends through an end wall of the filter housing to the exterior of the housing indicating presence of a properly installed filter cartridge. 
     In one aspect of the invention, the filter cartridge assembly includes a substantially rigid support tube having airflow apertures therethrough. A filter media is arranged on, surrounding and secured onto the outside surface of the support tube. An annular end cap is secured to a first axial end of the support tube and/or to the filter media. The support tube includes an axially outwardly projecting elastomeric annular sealing collar surrounding the open aperture in the end cap. A closed end cap is secured to an opposing second axial end of the support tube. The closed end cap includes a substantially rigid first end cap layer unitary with the support tube sidewall. An axially outwardly extending dome member is centrally arranged on the closed end cap. An anti-rotation engagement housing member is arranged on an outward facing surface of the dome member. The anti-rotation engagement member has a radially elongated or polygonal radial cross section configured to be received into and rotationally lock to the complimentary anti-rotation opening provided in and extending through an end face of the filter housing to lock locking rotational alignment of the first filter cartridge to the filter housing. A plurality of axially extending elastomeric projections is provided on an outward facing surface of the closed end cap encircling the dome member with circumferential gaps between the elastomeric projections. The elastomeric projections each have pre-defined keying characteristics including: A pre-defined arc length, wherein different ones of the axially extending elastomeric projections can have different lengths. A pre-defined projection length measured axially relative to the outward facing surface, wherein different ones of the axially extending elastomeric projections can have different projection lengths. A pre-defined axially extending elastomeric projection width, wherein different ones of the axially extending elastomeric projections can have different projection widths. A pre-defined gap spacing between adjacent elastomeric projections, wherein different pairs of the projections can have different gap spacings. A pre-defined number of the axially extending elastomeric projections. The pre-defined characteristics of the elastomeric projections and complimentary inward projections on the filter housing end face key a particular intended type of the filter cartridge for use in filter housing while excluding unsuitable or off specification filter cartridges. A continuous annular seal is arranged radially between the plurality of axially extending elastomeric projections and the dome member and projected axially outwardly from the outward facing surface of the second end cap layer, the annular seal configured to radially seal against the outward facing surface of an annular sealing projection provided on an interior of an adjacent housing end face. 
     In another aspect of the invention the filter cartridge assembly includes a secondary filter cartridge axially aligned with and radially nested within the open interior of the main filter cartridge. The second filter cartridge includes a substantially rigid support tube, an end cap extending over a first axial end of the support tube and formed as a unitary one piece component together with the support tube. An axially outwardly extending, substantially rigid and at least partially radially compressible crown is formed in one piece with or permanently secured to an axially outwardly facing surface of the secondary element end cap, The crown includes an axially aligned outwardly extending central projecting pin and a plurality of axially outwardly extending legs arranged radially encircling the projecting pin, the legs forming a tubular extension with axial slits separating the legs. The central projecting pin extends outwardly beyond the plurality of axially extending legs and is operable to absorb impact and protect the crown legs from impact damage. 
     In another aspect of the invention, the filter media of the secondary filter cartridge is a non-woven filter media including nylon, polyester, glass or polypropylene fibers. 
     In another aspect of the invention an elastomeric fixation ring is secured to an axially outwardly facing surface of the secondary element end cap. The elastomeric support ring has an open interior through which the crown axially projects. The elastomeric support ring is bonded to an edge portion of the secondary element filter media securing the secondary element filter media to the secondary element support tube. 
     In another aspect of the invention the secondary element filter media is secured to the secondary element support tube by welding. 
     In another aspect of the invention the secondary element filter media is secured to the secondary element support tube by metal or plastic clamp rings compressably mounting the secondary element filter media onto the secondary element support tube. 
     In another aspect of the invention the filter cartridge assembly includes a filter housing having an inlet connection for receiving unfiltered air. An outlet connection for filter air is arranged in a first end wall of the filter housing. A second opposing end wall of the filter housing includes an anti-rotation opening provided in a central portion of the end wall and extending from an interior of the filter housing to an exterior of the filter housing. A plurality of inwardly extending end wall projections are arranged on an inner surface of the end wall encircling the anti-rotation opening. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying Figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention. 
       Features of the present invention, which are believed to be novel, are set forth in the drawings and more particularly in the appended claims. The invention, together with the further objects and advantages thereof, may be best understood with reference to the following description, taken in conjunction with the accompanying drawings. The drawings show a form of the invention that is presently preferred; however, the invention is not limited to the precise arrangement shown in the drawings. 
         FIG. 1  depicts a sectional side view of an exemplary air filter system including an axially openable/serviceable filter housing and filter cartridge(s) removeably installed within the filter housing, consistent with the present invention; 
         FIGS. 2A-2C  depict perspective views of an exemplary main filter cartridge, consistent with the present invention; 
         FIGS. 3A and 3B  depict perspective views of an exemplary secondary filter cartridge configured to radially nest within and supportively engage with a main filter cartridge, such as the main filter cartridge of  FIGS. 2A-2C , consistent with the present invention; 
         FIG. 4A  depicts an exterior end wall view of a second housing part or housing cap illustrating features of the present inventive disclosure, consistent with the present invention; 
         FIG. 4B  depicts an interior view of the second housing part of  FIG. 4A , taken at the section line  4 B- 4 B of  FIG. 1 , depicting radially locking engagement of a main filter cartridge and filter housing, consistent with the present invention; 
         FIG. 5  depicts an enlarged view of the region identified as “ 5 ” in  FIG. 1 ; and 
         FIG. 6  depicts an enlarged view of the region identified as “ 6 ” in  FIG. 1 . 
     
    
    
     Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention. 
     DETAILED DESCRIPTION 
     Before describing in detail embodiments that are in accordance with the present invention, it should be observed that the embodiments reside primarily in combinations of apparatus components related to cartridge filters and the filter housing designed to receive such cartridge filters. Accordingly, the apparatus components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. 
     In this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element preceded by “comprises . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element. 
       FIG. 1  depicts a sectional side view of an exemplary air filter system  10 . The filter system  10  includes a first housing part  12  and an axially and sealably mating second housing part  14 . In the embodiment of  FIG. 1  the housing parts  12 ,  14  are detachably secured together by releasable mounting means, for example spring clamps or latches  16 . The second housing part  14  may be removed from the first housing part  12  in an axial direction by first releasing spring clamps  16 . 
     As defined herein, the “axial direction” is a direction parallel to the axis “A” as shown on  FIG. 1  corresponding to the central axis of the filter cartridge  26 . 
     In the exemplary embodiment of  FIG. 1  the inlet connection  18  is provided on the radially outer wall of the first housing part  12  and delivers air to be filtered (arrow “B 1 ”) tangentially into and along the inner circumference of the first housing part  12 . A tangential air delivery into the filter housing  12 , 14  is preferred as incoming air is then circumferentially swirled within the filter housing  12 , 14 , the filtration thereby benefiting from the inertial effects of the swirling air to separate particulates from the inlet air by centrifugal force before entering the filter cartridges. When the air inlet connection  18  is arranged tangentially as described above, it is preferred to provide a dust discharge valve  22  on the outer wall of the housing as shown later in  FIGS. 4A and 4B  to discharge accumulated dust from the filter housing. The illustrated dust discharge valve  22  is an elastomeric “duckbill” valve which is held closed by vacuum within the filter housing during operation and opens in response to pressure fluctuations or when the connected engine or compressor ceases operation. 
     An outlet connection  20  is provided on an end face  24  of the first housing part  12  (airflow according to arrow “B 2 ”). Preferably, for efficient utilization of space within the filter housing, the outlet connection  20  is concentrically positioned relative to the circumferential outer wall of the filter housing. 
     Arranged and enclosed within the filter housing  12 , 14  is a main filter cartridge  26  and optionally a secondary filter cartridge  28 . The secondary filter cartridge  28  is advantageously radially nested within the main filter cartridge and supportively engages the end cap  30  of the secondary filter cartridge  28  with the end cap  32  of the main filter cartridge, as described later. 
     The main filter cartridge  26  is depicted as an axially elongated cylindrical filter cartridge which includes a circumferentially closed filter media  34  circumferentially surrounding and supported against and secured to an air permeable support tube  36  (see discussion with  FIG. 1  above). Preferably the filter media  34  is a pleated paper filter media with media folds having ridges and valleys extending axially (direction of axis A) between the upper end cap  38  and the lower end cap  32  of the main filter cartridge  26 . 
     The support tube  36  preferably is made of a sufficiently rigid (stiff) plastic or metallic material such that the support tube  36  is operative to provide structural support to the filter media  34  so as to resist inwardly directed radial forces induced on the filter media  34  due to fluid flow through the filter media  34 . The support tube  36  includes a grille or grate structure surrounding air permeable apertures, such as shown in  FIG. 1 . Support tube  36  may alternately be realized as a solid tube, such as a plastic tube, provided with a plurality of spaced holes or apertures configured to permit air flow through the circumferential wall of the support tube. In other embodiments, airflow permeable wall portions of the support tube may be realized by other means, for example as a wire mesh. 
       FIGS. 2A-2C  depict perspective views of the exemplary main filter cartridge  26 . The main filter cartridge  26  is depicted as a axially elongated cylindrical filter cartridge which includes a circumferentially closed filter media  34  circumferentially surrounding and secured to an air permeable support tube  36  (see discussion with  FIG. 1  above). The main filter cartridge includes an upper end cap  38  and a lower end cap  32 . The main filter cartridge, as depicted in  FIG. 2A , is preferably a one-piece unit which is removeably and replaceably installed into a filter housing  12 ,  14  as a single monolithic replaceable or serviceable component. 
     The lower end cap  32  preferably is a two component end cap having a substantially rigid plastic cap layer  32 A, preferably a unitary one-piece component of the support tube  36 , overlaid by an elastomeric sealing material (example: polyurethane) molded onto or secured onto substantially rigid plastic cap layer  32 A of the support tube  36 . 
     The lower end cap  32  includes an axially outwardly extending dome member  40  having a receptacle  40  opening into the interior of the main filter cartridge  26 , the dome member includes an anti-rotation housing engagement member  42 , preferably formed unitary with the dome member. 
     The housing engagement member  42  may have an oval cross section, or preferably (as shown) the housing engagement member  42  is a “convex rectangular” cross section, where herein we define “convex rectangular” to be a two-dimensional shape having two parallel straight sides and closed at opposing ends by arc portions (not necessarily full semi-circles).  FIGS. 2B and 2C  show the housing engagement member  42  having the herein defined convex rectangular cross section. 
     Within the present invention the anti-rotation housing engagement member  42  may have other cross-sectional shapes, for example triangular or other polygonal shapes, oblong, ellipse, etc. Advantageously, the cross section of the anti-rotation housing engagement member  42  provides a rotationally locked engagement of the main filter cartridge  26  to the filter housing  14  end face. 
     As shown in  FIG. 2B  the substantially rigid plastic cap layer  32 A preferably is provided with a plurality of radially extending ribs with open spaces therebetween. The ribs and open spaces permit the overlaid elastomeric sealing material  32 B (example: polyurethane) to infiltrate into the substantially rigid plastic cap layer  32 A and securely engage to the substantially rigid plastic cap layer  32 A to form a monolithic or unitary lower end cap  32  which is preferably one piece with the support tube  36  and main filter cartridge  26 . 
     Advantageously, as shown on  FIGS. 2A and 2C , the lower end cap  32  of the main filter cartridge  26  includes a plurality of arcuate circular arc shaped projections  44 , the projections  44  extending axially outwardly from the lower end cap  32 . Preferably the projections  44  are formed into or molded onto the elastomeric sealing material  32 B of the lower end cap  32 . The arcuate circular arc shaped projections  44  each have predefined and possibly differing projection arc lengths AL, projection length PL and projection to projection spacing S operative to uniquely and positively “key” a particular service required type of main filter cartridge  26  with a desired/required service specification to the filter housing,  12 ,  14 , as will be explained in further detail below. 
     Although the arc shaped or arcuate projections are discussed herein and curved projections are shown on the drawings, it is to be understood that wherever the term “arcuate” is used, we hereby and herein define “arcuate” projections to include projections having any radius, including an infinite radius (i.e. linear/straight line/uncurved projections). 
     In some filter systems  10 , a secondary filter cartridge  28  or fine filter cartridge is radially nested within the open interior of the main filter cartridge  26  and arranged downstream with respect to flow relative to the main filter cartridge  26 . An exemplary secondary filter cartridge  28  is shown in  FIGS. 3A and 3B . 
     The secondary filter cartridge  28  includes an elongated, preferably cylindrical airflow permeable support tube  46 , preferably mountably engaging with the airflow outlet connection  20  and extending inwardly into the filter housing  12 ,  14  to radially nest within the interior of the main filter cartridge  26  (see  FIG. 1 ). The elongated support tube  46  may be generally cylindrical in shape having air permeable walls formed by a network of spaced ribs having airflow apertures therebetween. The ribs may also include cross members forming a grid like structure as the walls of the elongated support tube  46 . The secondary filter cartridge  28  support tube  46  includes a first axial end configured to detachably mount to the interior of the first housing part  12 , preferably a threaded connection into the interior wall of the outlet connection  20  of the first housing part  12 , although bayonet connections or a press-fit connection is also suitable and within the scope of the present inventive disclosure. 
     The support tube  46  forms a support member for the filter media  48  of the secondary filter cartridge  28 . The filter media  48  is arranged circumferentially on and circumferentially about the cylindrical wall of the support tube  46 . The filter media  48  is configured to close over all openings or apertures provided in the cylindrical wall of the support tube  46  (see  FIG. 1 ) such that air flowing from within the filter housings ( 12 ,  14 ) is required to flow through the secondary filter cartridge  28  before it can reach the outlet connection  20  to exit the filter housing. The support tube  46  is operative to provide structural support to the secondary filter cartridge  28  filter media  48  such that the filter media  48  may resist forces acting upon the filter media  48  such as due to air flowing through the secondary filter cartridge  28 . 
     The secondary filter cartridge  28  is positioned and arranged as an after filter or fine particle filter to the main filter cartridge  26 . The secondary filter cartridge  28  also serves to protect devices downstream of the air outlet connection  20  from receiving unfiltered, dirty or particulate contaminated air even if the main filter cartridge  26  fails or is not present in the filter housing ( 12 , 14 ), such as can occur (for example) when the main filter cartridge  26  is removed for servicing and/or replacement. 
     At the end axial end opposing the axial end  72  at which the secondary filter cartridge  28  detachably mounts to the filter housing  12 ,  14  (preferably by thread  72 ), the secondary filter cartridge  28  includes an end cap  50 . The filter media  48  is secured to the outer surface of the support tube  46  by polyurethane molding of the end cap  50  or alternately by welding of the filter media  48  onto the support tube  46 , welding preferably by ultrasonic welding, or alternately by the use of metal or plastic clamp rings clamping circumferentially onto the other surface of the filter media  48  compressibly securing the filter media  48  to the support tube  46 . The support tube  46  is preferably an injection molded plastic component of preferably PA6 GF30 or PPT20 material, although not limited to these materials. Opposing edges of the filter media sheet  48  may be secured together by a sewn seam  70  to secure the filter media  48  onto the support tube  46 . 
     Advantageously, the end cap  50  of the secondary filter cartridge  28  includes an axially outwardly extending and at least partially radially compressible (or deflectable) flexible crown  52  formed one piece with or permanently mounted to the end cap  50 . Although the crown  52  is somewhat deflectable, it is primarily substantially rigid so as to be operative to radially support the secondary filter cartridge  28  on the end cap of the main filter cartridge  26 . The crown  52  includes a plurality of axially extending legs  54  arranged surrounding a central rib or projecting pin  56 , the central projecting pin  56  formed one piece with or permanently mounted onto the end cap  50 , The central projecting pin may have a cross-shaped cross section as shown in  FIG. 3B , although other cross sections (for example square, circular, etc) are also within the invention. 
     Preferably the plurality of axially extending legs  54  are arranged on the end cap  50  in a circle encircling the projecting pin  56 , although other arrangements such as square, elliptical, etc. encircling the pin are envisioned and fall within the scope of the present inventive disclosure. Preferably the crown  52  is provided with six axially extending legs  54  as shown in  FIG. 3B , although the present invention is not limited to the use of exactly six legs  54  shown in  FIG. 3B . Any number of legs may be used. 
       FIG. 4A  depicts the filter housing end wall  58  viewed from the exterior of the second housing part  14  or housing cap. The end wall  58 , particularly on the interior side, includes a plurality of axially inwardly projecting end wall projections  60  formed in one piece with or secured onto the interior of the house  14  end wall  58 . Although shown for clarity, the end wall projections  60  in  FIG. 4A  are to be understood as arranged on the interior side of the end wall  58 . 
       FIG. 4B  is a section view of the end wall  58  of the second housing part  14  taken along the cutting line  4 B- 4 B of  FIG. 1 . Referring again to previously discussed  FIG. 1 , you will note that the main filter cartridge  26  is installed in the filter housing  14 . For illustration and discussion purposes, the cutting line  4 B- 4 B cuts through the axially extending arcuate projections  44  of the main filter cartridge  26  lower end cap  32 , as shown on and discussed previously with  FIGS. 2A and 2C . 
     In  FIG. 4B  the interposing “keyed” engagement of the arcuate projections  44  of the main filter cartridge  26  into the gaps between the axially inwardly projecting end wall projections  60  of the second housing part  14  is clearly shown. As can be seen in  FIG. 4B , the “keyed” engagement or interferences between the pre-defined spacing, quantity and individual lengths of the end wall projections  60  of the second housing part  14  and the complimentary pre-defined spacing, quantity and individual lengths of the arcuate projections  44  of the main filter cartridge  26  are operative to “key” or specifically select an appropriate filter cartridge suitable and adapted for the intended service for use within the filter housing  12 ,  14 , while advantageously excluding other filter cartridges having unsuitable specifications or unsuitable filtering, material properties for the service or unsuitable chemical properties. Advantageously, potentially damaging errors can be prevented by mechanically excluding through keyed interferences the accidental installation of incompatible or off-spec main filter cartridges into the filter housing  12 ,  14 . Also shown are the axially extending legs  54  of the crown  52  of the secondary filter cartridge  28 , compressed/deflected and received within the axially outwardly extending receptacle cup  40  formed into the end cap  32  of the main filter cartridge  26 . 
       FIG. 5  depicts an enlarged view of the region identified as “ 5 ” in  FIG. 1 , showing the lower end cap  32  of the main filter cartridge  26  with the axially outwardly projecting dome having receptacle cup  40  formed unitary/one-piece with the lower end cap  32  and receiving via interference fit the axially extending legs  54  of the flexible crown  52  of the end cap  50  of the secondary filter cartridge  28 . As can be seen in  FIG. 5 , the crown legs  54  are received against and slightly deflected by abutment against the radial inner surface  76  of the receptacle cup  40 . As discussed earlier, the crown, end cap  50  and the lower end cap  32  are substantially rigid, preferably molded plastic components. Radial engagement of the crown legs  54  into the receptacle cup  40  radially locks the position of the secondary filter cartridge  28  to the main filter cartridge  26 , providing radial support to the secondary filter cartridge at this axial end of the cartridge. Referring to  FIG. 1  it can be seen that the opposing axial end of the secondary filter cartridge is mounted to the first housing part  12  at the outlet connection  20  (preferably by threaded engagement of threads  72  on the secondary filter cartridge  28  and thread  78  on a housing projection concentric with the outlet connection  20 ) and therefore receives radial and axial support from the housing also at the end opposing the secondary filter cartridge end depicted in  FIG. 5 . Therefore with the radial engagement of the crown into the receptacle cup the secondary filter cartridge is fully supported at both ends within the main filter cartridge. 
     As can also be seen in  FIG. 5 , taken with reference to  FIG. 2C , the anti-rotation housing engagement member  42  formed in one piece with the receptacle cup  40  is received into and extends through a similarly/complimentary shaped anti-rotation housing opening  62  arranged in the end wall  58  of the second housing part  14 . In one exemplary embodiment the housing engagement member  42  may have an oval cross section (2 straight sides closed with semi-circular ends), or preferably as shown, the housing engagement member  42  is a “convex rectangular” cross section, “convex rectangular” as defined earlier with  FIGS. 2B and 2C  and more clearly shown in  FIGS. 2B and 2C . Referring also to  FIG. 4A , visible on the outside of the second housing part is the anti-rotation housing engagement member  42  projecting through the anti-rotation housing opening  62  in the end wall of the second housing part. The anti-rotation housing engagement member  42 , in addition to enforcing proper rotational alignment between the filter cartridge and the housing, advantageously also provides a visible indication of a properly installed filter element from the exterior of the filter housing. 
     As discussed earlier, in other embodiments of the invention the anti-rotation housing engagement member  42  may have other cross-sectional shapes, for example triangular or other polygonal shapes, oblong, ellipse, that “key” the rotational position of the main filter cartridge to the housing end cap by a rotationally locked engagement with the filter housing. Additionally, the cross sectional shape of the anti-rotation housing engagement member  42  and the similarly/complimentary shaped anti-rotation housing opening  62  are effective as an additional means to “key” the main filter cartridge to the filter housing (for example, by different cross sectional shapes or sizes), for the advantages as discussed earlier above with  FIG. 4B . 
       FIG. 6  depicts an enlarged view of the region identified as “ 6 ” in  FIG. 1 . In  FIG. 6  one of the arcuate projections  44  of the lower end cap  32  of the main filter cartridge  26  is shown extending axially outwardly into a gap between adjacent end wall projections  60  (see  FIG. 4B ). As discussed earlier with  FIG. 2C , the lower end cap  32  of the main filter cartridge is preferably a two component end cap having a substantially rigid plastic cap layer  32 A, preferably a unitary one-piece component of the support tube  26 , overlaid by an elastomeric sealing material  32 B (example: polyurethane) molded onto or secured onto the substantially rigid plastic cap layer  32 A of the support tube  26 . The elastomeric sealing material  32 B forms the arcuate projections  44  of the lower end cap  32 , which are therefore at least somewhat elastically compressible. In  FIG. 6  the illustrated arcuate projection  44  of the lower end cap  32  is schematically shown in a “relaxed” or “non-compressed” state projected axially outwardly beyond the end wall  58  of the second housing part  14 . In real life however, with the main filter cartridge installed in the filter housing, it is to be understood that the arcuate projection  44  of elastomeric sealing material  32 B is instead compressed against the inside surface of the end wall  58  and remains within and not extending through the end wall of the filter housing  14 . This compression of the arcuate projections  44  provides an axial force to the main filter cartridge  26  urging the main filter cartridge upwardly against the end face  24  of the first housing part, compressing the elastomeric annular sealing collar  64  to seal radially and/or axially with the first housing part  12  about the outlet connection  20 . 
     As can be understood by viewing  FIG. 6  together with  FIG. 2C  and  FIG. 4B , the arcuate projections  44  on the main filter cartridge end cap  32  “key” the filter cartridge to the filter housing and provide support to the main filter cartridge in the filter housing (above axial compression of arcuate projections  44 ), however the arrangement of the arcuate projections  44  and end wall projections  60  are insufficient to provide a seal between the interior of the filter housing and the outside environment (i.e. through then opening  62 ). Advantageously, annular seal  66  is formed on the elastomeric sealing material  32 B of the lower end cap  32  of the main filter cartridge  26 . The annular seal is a continuous annular ring extending axially outwardly from the lower end cap  32  and is configured to engage radially against the annular sealing projection  68  of the end wall  58  of the second housing part  14 . The radial sealing ( 68  engaging  66 ) is operative to seal the interior of the filter housing from the outside environment, thereby preventing flow through the anti-rotation housing opening  62  of the filter housing  14  and admittance of contaminated air through the anti-rotation housing opening  62 . 
     In the foregoing specification, specific embodiments of the present invention have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present invention. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.