Abstract:
The present disclosure provides apparatuses for filtering hot adhesives. In certain embodiments, the present disclosure provides a filter plate that is used in conjunction with a heater and a valve assembly. In other embodiments, the present disclosure provides a filter screen that is located in a recess of the valve assembly housing, in addition to or in lieu of the use of a separate filter plate. Both embodiments utilize one or more ribs, which aid the flow of adhesive, facilitate the transfer of heat from the heater to the valve assembly, and optionally, physically support the filter screen.

Description:
FIELD OF INVENTION 
       [0001]    The present invention generally relates to apparatuses for filtering hot adhesives, in particular, hot thermoplastic adhesives. 
       BACKGROUND OF INVENTION 
       [0002]    Apparatuses for delivering hot thermoplastic adhesives, sometimes referred to as “hot melt adhesives”, are known in the art. As shown in  FIGS. 1 and 2 , such apparatuses generally include a heater  12  to continue heating an adhesive and a valve assembly  14  directly attached to the heater  12 . The heater  12  generally includes a housing  54  and a heater exit aperture  52  located in the housing for delivering the adhesive from the heater housing  54  to the valve assembly  14 . The heater  12  may further include a clamp  49  for attaching the heater  12  to machinery. The heater  12  is connected to an external power source via a power cable  48 . The valve assembly  14  generally includes a valve assembly housing  15 , a valve assembly adhesive entrance aperture  24  for allowing the adhesive to enter the valve assembly housing  15 , a valve assembly adhesive exit aperture or nozzle  20  for allowing the adhesive to exit the valve assembly housing  15 , and a valve  17  having an open position in which the valve  17  permits the adhesive to exit the valve assembly housing  15  via the valve assembly adhesive exit aperture  20  and a closed position in which the valve  17  prevents the adhesive from exiting the valve assembly housing  15  via the valve assembly adhesive exit aperture  20 . Adhesives may be heated externally then conveyed into the heater housing  54 , where the heater  12  continues heating the adhesives. The adhesives then exit the housing  54  of the heater  12  through the heater adhesive exit aperture  52 , enter the housing  15  of the valve assembly  14  through the valve assembly adhesive entrance aperture  24 , and exit the valve assembly housing  15  through the valve assembly adhesive exit aperture  20 . After the exiting the valve assembly adhesive exit aperture  20 , the adhesive is ultimately applied to the target surface a number of different ways, including bead dispensing, non-contact spraying, and contact coating. 
         [0003]    In some prior art adhesive systems, the valve  17  is opened and closed via electricity, as shown in  FIG. 2 . In other prior art adhesive systems, the valve  17  is opened via pressurized air, in which case the heater  12  delivers pressurized air to the valve assembly  14 . In particular, air exits the housing  54  of the heater  12  through one or more heater to valve assembly air apertures  51 , enters the valve assembly housing  15  through one or more valve assembly air apertures  23 , and may exit the valve assembly housing  15  through a valve assembly air vent aperture  22 , as shown in  FIG. 1 . In one such design, the system includes two heater to valve assembly air apertures  51  and two valve assembly air apertures  23 , as shown in  FIG. 1 , in which case the valve  17  is both opened and closed via pressurized air. An opened air line may be used to open the valve  17  and a closed air line may be used to close the valve  17 . The opened and closed air lines may be two way air lines with air pressure moving the valve stem or piston to the open position and the closed air line venting the air from the closed side of the piston, and the closed air line may be pressurized moving the valve stem or piston to the closed position with the opened air line venting the air from the opened side of the piston. In another design (not shown), the valve assembly  12  includes only one heater to valve assembly air aperture  51  and only one valve assembly air aperture  23 , in which case the valve  17  may be opened via pressurized air and closed via a spring. A set screw  22 A may be available to set the valve stem or piston travel length. 
         [0004]    A problem with the systems described above is that particulate matter in the adhesives can clog the valve assembly adhesive exit aperture or nozzle  20  and/or valve  17  over time, leading to the inoperability of the valve assembly adhesive exit aperture or nozzle  20  and/or valve  17 . This problem is significant, given that many valves, such as those produced by Nordson Corp., are located in hard to reach places in the valve assembly housing  15 . Ultimately, many users decide to replace the entire valve assembly at a cost of approximately $100 to $1,000. 
         [0005]    As illustrated in  FIGS. 1 and 2 , and described in, for example, U.S. Pat. Nos. 6,799,702 and 6,315,168, an internal filter  68  disposed within the valve assembly housing  15  has been previously described. However, by disposing the filter  68  within the valve assembly housing  15 , the filter  68  cannot be replaced without disassembling the valve assembly housing  15 . 
         [0006]    U.S. Patent Publication No. 2008/0217360 discloses a filter screen that is located in a recess in the housing of the valve assembly so that an adhesive is delivered from the heater adhesive exit aperture  52  through the filter screen and into the valve assembly adhesive entrance aperture  24 . However, a potential problem with the system of U.S. Patent Publication No. 2008/0217360 is that contaminants stop the flow of adhesive when the limited area of the valve assembly adhesive entrance aperture  24  becomes covered and clogged as the adhesive flows from the heater adhesive exit aperture  52  through the small filter screen and into the small valve assembly adhesive entrance aperture  24 , which could occur in a short period of time. 
         [0007]    Therefore, there is a continuing need for new and better apparatuses for filtering hot adhesives. 
       SUMMARY 
       [0008]    The present disclosure provides apparatuses for filtering hot adhesives. In some embodiments, the present disclosure provides a filter plate for filtering an adhesive that includes: a) a proximal surface configured to face a heater; b) a distal surface configured to face a valve assembly; c) a filter plate adhesive recess located in the proximal surface; d) a filter plate adhesive exit aperture located in the recess and extending through the distal surface; and e) one or more ribs located in the recess, the ribs each having a rib base attached to a wall of the filter plate forming the recess and a rib apex extending proximally from the base. In use, a filter screen is located in the recess and the filter plate is positioned between a heater, which includes a heater housing and an adhesive exit aperture located in the housing allowing for flow of an adhesive, and a valve assembly, which includes a valve assembly housing, a valve assembly adhesive entrance aperture for allowing the adhesive to enter the valve assembly housing, a valve assembly adhesive exit aperture for allowing the adhesive to exit the valve assembly housing, and a valve having an open position in which the valve permits the adhesive to exit the valve assembly housing via the valve assembly adhesive exit aperture and a closed position in which the valve prevents the adhesive from exiting the valve assembly housing via the valve assembly adhesive exit aperture. Optionally, the filter screen is proximally disposed relative to the ribs and contacts the apexes of the ribs. The filter plate has a filter plate thickness extending from the proximal surface to the distal surface and optionally the filter plate thickness is from about 3 millimeters to about 7 millimeters. Optionally, two or more filter plates with filter screens having different sized apertures are disposed between the valve assembly and the heater for staged filtration. Optionally, the ribs or ribs assembly may be removable or a press fit configuration. 
         [0009]    In certain embodiments, the filter plate, heater and valve assembly are used in a method for filtering an adhesive that includes: 
         [0010]    a) providing the filter plate, valve assembly and heater; 
         [0011]    b) heating the adhesive in the heater housing; 
         [0012]    c) opening the valve; and 
         [0013]    d) delivering the adhesive from the heater adhesive exit aperture, through the filter screen, through the filter plate adhesive exit aperture, through the valve assembly adhesive entrance aperture, into the valve assembly housing and out of the valve assembly adhesive exit aperture. Optionally, the temperature of the adhesive drops not more than about 10° F. as the adhesive flows from the heater adhesive exit aperture to the valve assembly adhesive exit aperture. 
         [0014]    In an alternative embodiment, in addition to or in lieu of a separate filter plate, the ribs and filter screen are located in a recess of the valve assembly housing. 
         [0015]    Without being bound by any particular theory, it is believed that, whether the ribs are provided in the recess of the valve assembly housing and/or in the recess of the filter plate, the ribs aid and direct the flow of adhesive, facilitate the transfer of heat from the heater to the valve assembly, and optionally, physically support the filter screen. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    These and other features, aspects, and advantages of the invention will become better understood with regard to the following description, appended claims, and accompanying drawings where: 
           [0017]      FIG. 1  is a side view of a prior art heater and an air-operated valve assembly. 
           [0018]      FIG. 2  is a side view of a prior art heater and an electric valve assembly. 
           [0019]      FIG. 3  is a side view showing the assembly of an adhesive filtration system of one embodiment of the present invention, wherein a sectional view of the proximal filter plate is provided. 
           [0020]      FIG. 4  is a side view showing an assembled adhesive filtration system of one embodiment of the present invention. 
           [0021]      FIG. 5  is a proximal, perspective view of a filter plate of one embodiment of the present invention. 
           [0022]      FIG. 6  is a distal view of the filter plate shown in  FIG. 5 . 
           [0023]      FIG. 7  is a proximal, perspective view of a filter plate and valve assembly of one embodiment of the present invention. 
           [0024]      FIG. 8  is a distal, perspective view of a filter plate and heater of one embodiment of the present invention. 
           [0025]      FIG. 9  is a proximal view of a filter plate of one embodiment of the present invention. 
           [0026]      FIG. 10  is a sectional view of the filter plate of  FIG. 9 , taken along line  10 - 10  of  FIG. 9 . 
           [0027]      FIG. 11  is a distal view of a filter plate of one embodiment of the present invention. 
           [0028]      FIG. 12  is a proximal view of the filter plate of  FIG. 11 . 
           [0029]      FIG. 13  is a sectional view of the filter plate of  FIG. 12 , taken along line  13 - 13  of  FIG. 12 . 
           [0030]      FIG. 14  is a proximal view of a filter plate of one embodiment of the present invention. 
           [0031]      FIG. 15  is a sectional view of the filter plate of  FIG. 14 , taken along line  15 - 15  of  FIG. 14 . 
           [0032]      FIG. 16  is a proximal view of a filter plate of one embodiment of the present invention. 
           [0033]      FIG. 17  is a sectional view of the filter plate of  FIG. 16 , taken along line  17 - 17  of  FIG. 16 . 
           [0034]      FIG. 18  is a proximal view of a filter plate of one embodiment of the present invention. 
           [0035]      FIG. 19  is a sectional view of the filter plate of  FIG. 18 , taken along line  19 - 19  of  FIG. 18 . 
           [0036]      FIG. 20  is a proximal view of a filter plate of one embodiment of the present invention. 
           [0037]      FIG. 21  is a distal view of a filter plate of one embodiment of the present invention. 
           [0038]      FIG. 22  is a side view of the filter plate of  FIG. 21 . 
           [0039]      FIG. 23  is a proximal view of the filter plate of  FIG. 21 . 
           [0040]      FIG. 24  is a sectional view of the filter plate of  FIG. 23 , taken along line  24 - 24  of  FIG. 23 . 
           [0041]      FIG. 25  is a sectional view of the filter plate of  FIG. 23 , taken along line  25 - 25  of  FIG. 23 . 
           [0042]      FIG. 26  illustrates a proximal view of a filter screen and an O-ring of one embodiment of the present invention. 
           [0043]      FIG. 27  illustrates a proximal view of a filter screen and an O-ring of one embodiment of the present invention. 
           [0044]      FIG. 28  illustrates a proximal view of a filter screen and an O-ring of one embodiment of the present invention. 
           [0045]      FIG. 29  illustrates a proximal, perspective view of a filter screen and an O-ring of one embodiment of the present invention. 
           [0046]      FIG. 30  illustrates a side, cross-sectional view of a filter plate of one embodiment of the present invention. 
           [0047]      FIG. 31  illustrates an exploded proximal, perspective view of a filter plate of one embodiment of the present invention; arrows illustrate the flow of an adhesive through a grid created by the ribs. 
           [0048]      FIG. 32  illustrates an exploded proximal, perspective view of a filter plate of one embodiment of the present invention. 
           [0049]      FIG. 33  illustrates a proximal, perspective view of a valve assembly of one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0050]    Referring now to the drawings,  FIGS. 3-32  illustrate components of an adhesive filtration system generally designated by the numeral  11 . In the drawings, not all reference numbers are included in each drawing for the sake of clarity. In addition, positional terms such as “horizontal,” “vertical,” “upper,” “lower,” “side,” “top,” “bottom,” etc. refer to the apparatus when in the orientation shown in the drawing. The skilled artisan will recognize that the apparatus can assume different orientations when in use. 
         [0051]    Referring further to  FIGS. 3-32 , the system  11  includes a heater  12 , a valve assembly  14  and a filter plate  10 . The heater  12  includes a housing  54 , a thermoplastic adhesive disposed within the heater housing  54 , a heating element  70  to heat the heater  12 , and a power supply coupled to the heating element  70  for powering the heating element  70 . Preferably, the heating element  70  is configured to heat the adhesive to a temperature of at least 250° F., e.g., a temperature of from about 250° F. to about 450° F. The power supply is located outside the housing  54  and the heating element  70  is coupled to the external power supply via a cable  48 , as shown in  FIGS. 3 and 4 . The heater  12  further includes a heater exit adhesive exit aperture  52  for dispensing an adhesive. Optionally, the heater  12  further includes two or more threaded fastener apertures  16  for securing the filter plate  10  between the valve assembly  14  and the heater  12  via a fastener  19 . Optionally, the heater  12  includes a clamp  49  for securing the heater  12  to machinery. Optionally, if the heater  12  is used in conjunction with a valve assembly  14  that is operated by air, the heater  12  includes an external air aperture  50  and one or more heater to valve assembly air apertures  51 . Heaters  12 , also referred to as heated manifolds or blocks,  12  are well-known to those of ordinary skill and are commercially available from companies such as Illinois Tool Works (ITW), Glenview, Ill. 
         [0052]    The system further includes a valve assembly  14 . The valve assembly  14  includes a valve assembly housing  15 , a valve assembly adhesive entrance aperture  24  for allowing the adhesive to enter the valve assembly housing  15 , a valve assembly adhesive exit aperture or nozzle  20  for allowing the adhesive to exit the valve assembly housing  15  and a valve  17 . The valve  17  has an open position in which the valve  17  permits the adhesive to exit the valve assembly housing  15  via the valve assembly adhesive exit aperture  20  and a closed position in which the valve  17  prevents the adhesive from exiting the valve assembly housing  15  via the valve assembly adhesive exit aperture  20 . Optionally, the valve assembly  14  includes a valve assembly air vent aperture  22 . Optionally, the valve assembly  14  includes a valve stem or piston and a set screw  22 A is used to set the valve stem or piston travel length. In certain embodiments, the valve  17  is moved from the open to the closed position via electricity. For valves  17  that are operated by electricity, the electric valve assembly  14  may be directly connected to the power supply or the electric valve assembly  14  may be coupled to the heater  12 , which, in turn, is directly connected to the power supply. In other embodiments, the valve  17  is opened via pressurized air. In one such embodiment, the valve  17  is opened via air and closed via a spring, in which case the valve assembly  14  typically includes one valve assembly air aperture  23 . In another embodiment, the valve  17  is both opened and closed via air. An opened air line may be used to open the valve  17  and a closed air line may be used to close the valve  17 . The opened and closed air lines may be two way with air pressure moving the valve stem or piston to the open position and the closed air line venting the air from the closed side of the piston, and the closed air line may be pressurized moving the valve stem or piston to the closed position with the opened air line venting the air from the opened side of the piston. It will be understood that the operation of the valve assembly  14  described above is merely exemplary and the systems  11  of the present disclosure may be used with any valve assembly  14  that is suitable for use in conjunction with heated thermoplastic adhesives. Optionally, the valve assembly housing  15  has a large cut-out  78 , as shown in  FIG. 7 . Valve assemblies used with heated thermoplastic adhesives and methods of opening valves  17  via, for example, pistons and solenoids, are described in, for example, U.S. Pat. Nos. 6,315,168, 5,672,269 and 6,799,702, the contents of each of which are incorporated by reference herein in their entirety. Optionally, the valve assembly  14  further includes an interior filter  68  disposed in the housing  15  as described in, for example, U.S. Pat. Nos. 6,315,168 and 6,799,702. Preferably, the valve assembly  14  is configured to transport thermoplastic adhesives having a temperature of at least 250° F. Optionally, the valve assembly air aperture  23  and the valve assembly adhesive entrance aperture  24  are located in recesses  33  and  25  in the valve assembly housing  14 , as exemplified in  FIGS. 7 , and O-rings  31  and  21  are positioned in the recesses  33  and  25 , when the system  11  is in use. Optionally, the valve assembly  14  further includes two or more fastener apertures  18  for securing the valve assembly  14  and the filter plate  10  with the heater  12 . Optionally, the adhesive exit aperture  20  is disposed at about a 90 degree angle with respect to the adhesive entrance aperture  24 , as illustrated in  FIGS. 3 ,  4  and  7 . 
         [0053]    The system  11  further includes one or more filter plates  10  positioned between the heater  12  and the valve assembly  14 . The filter plate  10  has a proximal surface  44  configured to face the heater housing  54  and a distal surface  46  configured to face the valve assembly housing  15 . The filter plate proximal surface  44  includes an adhesive recess  34 . A filter plate adhesive exit aperture  38  is located in a wall  56  of the filter plate  10  forming the adhesive recess  34  (e.g., the distal-most wall of the adhesive recess  34 , as best seen in  FIG. 32 ) and extends through the distal surface  46 . The filter plate  10  further includes one or more filter plate ribs  36 . Alternatively, the ribs  36  may be removable. Each rib includes a rib base  58 , which may be attached to a wall  56  of the filter plate  10  forming the adhesive recess  34  (e.g., the distal-most wall of the adhesive recess  34 , as best seen in  FIG. 32 ) and a rib apex  60 , which extends proximally from the rib base  58 . Preferably, the apexes  60  of the ribs are flat, as illustrated in  FIGS. 5 ,  7 ,  31  and  32 ). Alternatively, the apexes  60  may be rounded. The filter plate  10  further includes a filter screen  40  located in the recess  34 . The filter screen  40  may be, for example, a wire screen. Preferably, the filter screen  40  is comprised of aluminum, stainless steel and/or a metal alloy. Illustrative designs of the filter screen  40  are shown in  FIGS. 26-28 . It will be appreciated that the patterns shown in  FIGS. 26-28  are merely exemplary and other patterns may be utilized in conjunction with the present disclosure. 
         [0054]    Preferably, the filter screen  40  is disposed proximally relative to the ribs  36  and the apexes  60  of the ribs  36  contact and support the filter screen  40 . Preferably, the filter screen  40  is removable so the filter screen  40  can be cleaned or replaced with a different filter screen  40 , depending on the needs of the person operating the system  11 . Optionally, the filter plate  10  further includes two or more fastener apertures  26  for securing the filter plate  10  between the valve assembly  14  and the heater  12 . Further, if the valve  17  is opened by air, preferably, the filter plate  10  includes one or more air apertures  28  so that air may be delivered from the heater to valve assembly air aperture(s)  51  through the filter plate air aperture(s)  28  and into the valve assembly air aperture(s)  23 . Optionally, the filter plate  10  further includes a filter plate air aperture recess  29  located in the proximal surface  44  and an O-ring  30  is placed in the filter plate air aperture recess  29  so that the filter plate  10  creates a seal when the proximal surface  44  is placed against either the heater housing  54  or the distal surface  56  of another filter plate  10 . Optionally, the filter screen  40  is secured to the filter plate  10  by an O-ring  42 . In such embodiments, the O-ring  42  may be integral with the filter screen  40  or may rest on a border  41  surrounding the filter screen  40  when the filter screen  40  is placed in the adhesive recess  34 . Preferably, the O-ring  42  completely covers the border  41  so the adhesive is guided through the filter screen  40 . The O-ring  42  preferably forms four purposes: 1) attaching and sealing the filter screen  40  to the adhesive recess  34 ; 2) facilitating the flow of the adhesive through the filter screen  40 ; 3) providing as large a reservoir as possible where debris may accumulate without hindering the flow of the adhesive; and 4) sealing the adhesive exit aperture  52  of the heater  12  or additional stackable filter plates. Preferably, the O-ring  42  rests on the filter screen  40 , which rests on a ledge  35  of the filter plate, and the ledge  35  is heated by the adhesive and heat is transferred through the filter plate  10 . The ribs  36  preferably perform three purposes: 1) physically supporting the filter screen  40 ; 2) creating a grid  37  that helps direct the flow of the adhesive into the adhesive exit aperture  38  (as best seen in  FIGS. 31 ); and 3) increasing the surface area of the filter plate  10  that the adhesive contacts so as to minimize heat loss as the adhesive moves from the heater adhesive exit aperture  52  and into the valve assembly adhesive entrance aperture  24 . 
         [0055]    Optionally, as illustrated in  FIGS. 7 and 8 , the filter plate  10  has a large cut-out  80 . Optionally, as exemplified in  FIG. 20 , the filter plate  10  is configured to be used in conjunction with different valve assemblies  14  and heaters  12 , in which case the filter plate  10  has several different adhesive apertures  38 , fastener apertures  26 , and air apertures  28  so that the same filter plate  10  may be used with different valve assemblies  14  and heaters  12 . 
         [0056]    An exemplary method of operation of the system  11  will now be described. A system  11  including a heater  12 , a valve assembly  14  and one or more filter plates  10  is assembled, as described above. The adhesive temperature is maintained in the heater  12 . The valve  17  is opened. The adhesive is delivered from the heater adhesive exit aperture  52 , through the filter screen  40 , through the filter plate adhesive exit aperture  38 , through the valve assembly adhesive entrance aperture  24 , into the valve assembly housing  15  and out of the valve assembly adhesive exit aperture  20 . Preferably, if the valve  17  is opened by air, the method further includes delivering air from the heater to valve assembly air aperture  51 , through the filter plate air aperture  28  and into the valve assembly air aperture  23  so as to open the valve  17 . The skilled artisan will appreciate that the above method may be performed in any suitable order. For example, the valve  17  may be opened before, simultaneous with or after the adhesive is delivered from the heater adhesive exit aperture  52 . Preferably, the filter plate  10  is configured to withstand temperatures between 250° F. and 450° F. 
         [0057]    Preferably, the system  11  is configured so as to minimize the loss of heat as the adhesive moves from the heater adhesive exit aperture  52  and into the valve assembly adhesive entrance aperture  24  so the adhesive maintains temperature. Preferably, the temperature of the adhesive drops no more than about 5° F. as the adhesive moves from the heater adhesive exit aperture  52  and ultimately out of the valve assembly adhesive exit aperture  20 . For example, as shown in  FIG. 6 , the filter plate  10  has a thickness  66  that extends from the proximal surface  44  to the distal surface  46  and it is believed that a filter plate thickness  66  of from about 3 millimeters to about 7 millimeters (e.g., about 5 millimeters) will minimize heat loss. For example, it has been observed that having a filter plate thickness  66  of about 5 millimeters results in a temperature drop of less than 5° F. to the valve assembly adhesive exit aperture  20  if one filter plate  10  is used and a temperature drop of less than 8-10° F. if two filter plates  10  are used. The heater  12  temperature may be adjusted to compensate for this drop. Further, it is believed that assembling the system  11  such that the proximal surface  44  of the filter plate  10  contacts the valve assembly  14  or another filter plate  10  and the distal surface  46  contacts the heater  12  or another filter plate  10  will minimize heat loss. 
         [0058]    Preferably, the components of the filter plate  10  are configured so as to facilitate the movement of the adhesive. For example, the adhesive exit aperture  38  may be located near the center of the wall  56  (as illustrated in  FIGS. 5 ,  9 ,  10 ,  16 ,  17 ,  20 , and  31 - 32 ) or near an edge of the wall  56  (as illustrated in  FIGS. 7 ,  12 - 15  and  18 - 19 , and  23 - 24 ). Further, the longitudinal axes  64  of the ribs  36  may be perpendicular to the longitudinal axis  62  of the valve assembly  14  (as illustrated in  FIGS. 3 ,  5 ,  9 ,  10 ,  16 ,  17  and  30 - 32 ). Alternatively, the longitudinal axes  64  of the ribs  36  may be parallel to the longitudinal axis  62  of the valve assembly  14  (as illustrated in  FIGS. 7 ,  12 - 15 ,  18 - 19 ,  23 - 25  and  30 ). Preferably, the valve assembly  14 , filter plate  10 , and filter screen  40  are comprised of aluminum, stainless steel and/or a metal alloy. 
         [0059]    In designing the configuration of the ribs  36 , it will be appreciated that a sufficient number of ribs  36  should be provided in order to maximize the surface area of the plate  10  that is exposed to the heated adhesive. However, it also will be appreciated that ribs  36  should not be placed so close together that the ribs  36  hinder the flow of the adhesive. 
         [0060]    Preferably, if the system  11  includes two or more filter plates  10 , the filter plates  10  have filter screens  40  with different sized apertures and the filter plate  10  with a filter screen  40  having larger apertures is located next to the heater  12  and the filter plate  10  with a filter screen  40  having smaller apertures (as compared to the other filter screen  40 ) is located next to the valve assembly  12  (and distal to the other filter plate  10 ) so that the adhesive flows through the filter screen  40  having larger apertures first. 
       The Alternative Embodiment of FIG.  33   
       [0061]    Instead of, or in addition to, having ribs and a filter screen located on a filter plate, as described above, the ribs and filter screen may be located in a recess in the housing of a valve assembly, as shown in  FIG. 33 . In this alternative embodiment, components having the same function and structure as components described above will be designated with the same numeral with an apostrophe after the numeral to indicate that the component corresponds to the embodiment of  FIG. 33 . 
         [0062]    In the alternative embodiment, the system includes a heater having the same components and structure described with the prior embodiments and, optionally, a filter plate having the same components and structure described with the prior embodiments. The system further includes a valve assembly  14 ′. The valve assembly  14 ′ has the same components and structure described with the prior embodiments (including but not limited to the housing  15 ′, the valve assembly air apertures  23 ′, the air recesses  33 ′, the air aperture O-rings  31 ′, the fastener apertures  18 ′, the valve  17 ′, the internal filter  68 ′, the air vent aperture  22 ′, the adhesive exit aperture or nozzle  20 ′ and the longitudinal axis  62 ′) except that the ribs  36 ′ and filter screen  40 ′ are located in the adhesive recess  25 ′ of the valve assembly housing  15 ′. More particularly, the housing  15 ′ includes a proximal surface  72 ′ (which faces the heater and optionally a distal surface of a filter plate if a filter plate is also used), an opposite distal surface  74 ′, and the adhesive recess  25 ′ is located in the proximal surface  72 ′. The ribs  36 ′, each have a base  58 ′ attached to a wall  76 ′ of the housing  15 ′ forming the recess  25 ′ (e.g., the distal-most wall of the recess  25 ′) and an apex  60 ′ extending proximally from the base  58 ′. The valve assembly adhesive entrance aperture  24 ′ is located in a wall of the housing  15 ′ forming the recess  25 ′ (e.g., the distal-most wall of the recess  25 ′). A filter screen  40 ′ is removably attached to the recess  25 ′. Optionally, the filter screen  40 ′ is attached to the recess via an O-ring  42 ′ that rest on the filter screen  40 ′, as described in the prior embodiments. 
         [0063]    The ribs  36 ′ preferably perform three purposes: 1) physically supporting the filter screen  40 ′; 2) creating a grid  37 ′ that helps direct the flow of the adhesive into the valve assembly adhesive entrance aperture  24 ′; and 3) increasing the surface area of the valve assembly housing  15 ′ that the adhesive contacts so as to maintain heat of a larger area of adhesive as it moves from the heater adhesive exit aperture and into the valve assembly adhesive entrance aperture  24 ′. 
         [0064]    Preferably, as with the prior embodiments, the system of  FIG. 33  is configured so as to minimize the loss of heat as the adhesive moves from the heater adhesive exit aperture and into the valve assembly adhesive entrance aperture  24 ′. Preferably, the temperature of the valve assembly  14  does not drop when secured to the heater  12 . For example, a filter plate is used in conjunction with the alternate embodiment, the filter plate preferably has a thickness of from about 3 millimeters to about 7 millimeters (e.g., about 5 millimeters). Further, it is believed that assembling the system such that the proximal surface  72 ′ of the valve assembly  14 ′ contacts the heater or a filter plate will minimize heat loss. 
         [0065]    Preferably, the components of the valve assembly  14 ′ are configured so as to facilitate the movement of the adhesive. For example, the valve assembly adhesive entrance aperture  24 ′ may be located near the center of the wall  76 ′ (as illustrated in  FIG. 33 ) or near an edge of the wall  76 ′. Further, the longitudinal axes  64 ′ of the ribs  36 ′ may be perpendicular to the longitudinal axis  62 ′ of the valve assembly  14 ′ (as illustrated in  FIG. 33 ). Alternatively, the longitudinal axes  64 ′ of the ribs  36 ′ may be parallel to the longitudinal axis  62 ′ of the valve assembly  14 ′. Preferably, the valve assembly  14 ′, filter plate (if used), and filter screen  40 ′ are comprised of aluminum, stainless steel and/or a metal alloy. 
         [0066]    For the purposes of the present disclosure, use of the singular encompasses use of the plural. For example, as previously indicated, the systems may include multiple filter plates and multiple screens, as indicated previously. In addition, other parts may be duplicated, depending on the needs of the operator. Having now described the invention in accordance with the requirements of the patent statutes, those skilled in the art will understand how to make changes and modifications to the disclosed embodiments to meet their specific requirements or conditions. Changes and modifications may be made without departing from the scope and spirit of the invention, as defined and limited solely by the following claims.