Abstract:
A conventional liquid spray gun having a compressed air supply equipped with a liquid, e.g. paint, container for supplying the liquid to be sprayed onto a target surface. The container has a closed bottom, an open top and a cylindrical sidewall. A removable cover is attached over the open top of the container, and the cover has a pair of apertures extending through it, one of which holds a proximal end of a rigid tube whose distal end extends to a point close to the container&#39;s bottom. Slidingly mounted on the rigid tube is a generally circular, movable plunger whose periphery engages the cylindrical sidewall of the container. Pressurized air injected through the second aperture in the cover forces the plunger against the liquid&#39;s surface and causes the liquid to flow through the lumen of the rigid tube to the liquid inlet port of the spray gun.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a non-provisional application claiming the benefit of U.S. Provisional Application Ser. No. 61/000,390, filed Oct. 25, 2007, and which is deemed incorporated by reference herein in its entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]    II. Field of the Invention 
         [0003]    This invention relates generally to liquid supply apparatus for spray guns, and more particularly to an air pressure-assisted liquid supply apparatus attachable to a liquid input port of a spray gun. 
         [0004]    III. Discussion of the Prior Art 
         [0005]    Various liquid supply devices are known in the art for supplying mixtures of component liquids to be sprayed via air-powered spray guns, such as those commercially available from Sata Earbspritzechnik GmbH &amp; Co., Lex-Aire Products, Inc. of North Billerica, Mass., Graco, Inc. of Minneapolis, Minn., and a model available from Wagner Spray Tech Corporation of Minneapolis, Minn. 
         [0006]    U.S. Pat. Nos. 6,752,179, 6,796,514 and 6,953,155 each describe a cup-like assembly for feeding liquid to the inlet port of such spray guns. In each of those patented arrangements, the liquid to be sprayed is contained within a collapsible polymeric bag and the bag is, in turn, disposed in a rigid cup-like housing. An adapter designed to mate with the inlet connection of a particular spray gun is in fluid communication with the contents of the bag. When air under pressure is introduced in the space between the bag and the rigid housing, the bag is compressed forcing the liquid contents thereof out through the adapter and into the inlet port of the spray gun with which the liquid feeding assembly is attached. 
         [0007]    In so-called “gravity-fed units”, the liquid inlet for the spray gun projects upward from the barrel of the gun and the cup assembly with its tubular adapter is inverted when joined to the gun&#39;s inlet. Gravity and/or the Venturi-effect produced by high velocity flow air through a nozzle are used to draw the liquid from the flexible bag and into the air stream ultimately exiting the barrel of the spray gun. Again, as the liquid is extracted from the flexible bag, it collapses. Here, reference is made to the Schwartz U.S. Pat. No. 6,796,514 as an example of a prior art gravity-fed spray gun. 
         [0008]    One problem associated with gravity feed is that the spray pattern tends to be position sensitive. That is to say, when the liquid supply cup is disposed above the gun barrel, an adequate stream of liquid is drawn from the cup and mixed with the air stream to provide a full coverage pattern. However, if the shape of the object being treated, e.g. spray painted, necessitates inverting the gun such that the supply cup is disposed below the gun barrel, the suction force due to the Venturi nozzle may be insufficient to draw an adequate quantity of the liquid, creating an uneven pattern. 
         [0009]    Accordingly, a need exists for an improved pressurized liquid supply device for use with a spray gun. 
       SUMMARY OF THE INVENTION 
       [0010]    In accordance with a first embodiment of the invention there is provided a rigid plastic or metal container having a cylindrical sidewall, a closed bottom and an open top with a removable cover closing the container&#39;s open top. The cover has first and second apertures formed through its thickness dimension. A generally rigid tube extends through the first aperture and extends toward, but short of, the container&#39;s closed bottom. A movable plunger is slidably disposed on the rigid tube and is dimensioned to wipe against the cylindrical sidewall of the container as the plunger is made to move from a first position proximate the removable top to a second position proximate the closed bottom such that the plunger&#39;s descent displaces liquid from the container through a lumen of the rigid tube. Means are provided for attaching the container to an air-operated spray gun such that liquid passing through the lumen of the rigid tube feeds the liquid to the spray gun. A connection is made between the spray gun and the second aperture in the cover allowing pressurized air to enter the container at a location above the movable plunger to thereby force the plunger downward against the surface of the liquid in the container. 
         [0011]    In a further embodiment, a disposable, single-use liner is provided that closely conforms to the bottom and cylindrical sidewall of the rigid container, the use of which facilitates clean-up of the container assembly following job completion or a desired paint color change. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0012]    The foregoing features, objects and advantages of the invention will become apparent to those skilled in the art from the following detailed description of a preferred embodiment, especially when considered in conjunction with the accompanying drawings in which like numerals in the several views refer to corresponding parts. 
           [0013]      FIG. 1   a  is a longitudinal cross-sectional view taken through the center of the cup assembly with the plunger proximate the top of the cup; 
           [0014]      FIG. 1   b  is similar to  FIG. 1   a  but with the plunger proximate the midpoint of its travel; 
           [0015]      FIG. 1   c  is a view like  FIG. 1   a  but with the plunger proximate the bottom of the cup; 
           [0016]      FIG. 2  is an exploded view of the embodiment of  FIG. 1   a;    
           [0017]      FIG. 3  is a side elevation view of a spray gun with which the present invention finds use; and 
           [0018]      FIG. 4  is a front end view of the spray gun. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0019]    Certain terminology will be used in the following description for convenience in reference only and will not be limiting. The words “upwardly”, “downwardly”, “rightwardly” and “leftwardly” will refer to directions in the drawings to which reference is made. The words “inwardly” and “outwardly” will refer to directions toward and away from, respectively, the geometric center of the device and associated parts thereof Said terminology will include the words above specifically mentioned, derivatives thereof and words of similar import. 
         [0020]    Referring first to  FIG. 1   a,  there is illustrated a liquid supply apparatus adapted for attachment to a commercially-available air-operated spray gun, such as shown in  FIGS. 3 and 4 . The liquid in question may be a paint mixture, an adhesive or any one of a number of liquids to be applied as a coating on a substrate. For convenience, throughout the following description, the liquid will be referred to as spray paint that typically includes a pigment mixed with a volatile solvent that is of a viscosity permitting it to be applied as a fine spray when entrained in an air stream controlled by a pistol-like spray gun. 
         [0021]    The liquid supply attachment is indicated generally by numeral  10  and is seen to comprise a cylindrical cup  12  having a closed bottom end  14  and an open upper end  16 . The lower end is shown as including a recessed portion  17  in  FIG. 1   a.  A base member  19  fits onto the bottom of the cup permitting the cup to better stand upright on a flat surface. The cup member  12  may be fabricated from a suitable rigid plastic or a metal, such as aluminum, and it is provided with external threads  18  located proximate its periphery at the upper end  16 . The cup is preferably formed from a transparent plastic allowing the user to view the contents of the cup as a spray paint job progresses. Graduated markings as shown in  FIG. 2  may also be provided to indicate the volume of paint present at any given time. 
         [0022]    After the cup has been filled with paint to be sprayed, the open upper end of the cup member  12  is adapted to be closed by a cover member  20 , which is designed to rest upon the upper edge surface of the cup  12  having an upper surface  24  and a downwardly depending cylindrical flange  26  that is internally threaded so as to mate with the threads  18  of the cup member  12 . An O-ring or a flat gasket type seal  28  is placed between the cover member  20  and the upper edge of the cup member  12  so that when the cover member  20  is screwed down, a seal is created preventing escape of the liquid contents of the cup member  12 . 
         [0023]    With continued reference to  FIG. 1   a,  disposed within the cup member  12  and closely adhering to the cylindrical sidewall  13  and the bottom wall  14  is an optional molded plastic liner  30  represented by a heavy black line in the drawing. The liner may be disposable after a single use which obviates the need for cleaning the interior wall surface of the cup  12  between successive uses. Because the liner  30  need not be collapsed, as in the cited 3M patents, it can be made to have a thicker wall if reuse is desired. As can be further seen in  FIG. 1   a,  the upper rim of the liner  30  is captured between the cover  20  and the upper edge of the cup member  12  and provides a seal that precludes spray paint or the like from finding its way between the inner wall of the cup member  12  and the outer wall of the liner  30 . 
         [0024]    The cover member  20  has a frusto-conical dome shape that includes a central bore  32  into which is fitted a generally rigid or semi-rigid tube  34 . The tube  34  extends toward, but ends just short of, the bottom wall  14  of the cup member  12  so that its lumen is not occluded by the bottom end  14 . An optional basket-shaped screen filter  35 , that fits within the recess  17  formed in the bottom end  14 , is frictionally attached to the lower end of rigid tube  34 . The filter precludes thickened globs of paint from entering the tube  34  and possibly occluding the spray gun&#39;s needle valve. The cover member  20  further includes a second bore  36  extending parallel to the bore  32  in which the tube  34  is made to fit. The bore  36  serves as an air passage through the thickness dimension of the cover  20 , as will be further explained herein below. 
         [0025]    Placed atop the cover member  20  and held in place by threads  38 , in one embodiment, is an adapter member  40  comprising a double lumen tube. The first lumen  42  extends the length of the adapter  40  and is in fluid communication with the lumen of the tube  34  that extends through the center of the dome  20 . The second lumen of the adapter  40  is identified by numeral  46  and extends from an internally threaded opening  48  at the upper end of the adapter  40  to the bottom of the adapter where it is exposed to a chamber  50 . A hose nipple  49  fits into threaded opening  48  whereby a short length of hose (not shown) is used to connect to the nipple  49  and to an air outlet  74  of a spray gun, as at  53  in  FIG. 3 . On some commercially available spray guns, the air outlet fitting is located on the gun&#39;s handle, as at  75  in  FIG. 3 . Alternatively, an air compressor may be coupled to a port  51  leading to the chamber  50 . Adapter  40  could also be designed to directly couple to a customized spray gun and include internal passages for both paint and compressed air. This would eliminate the need for external hose to deliver compressed air from the spray gun to the cup assembly. 
         [0026]    A plunger, indicated generally by numeral  52 , is slidingly mounted with respect to the outer wall of the tube  34  and is seen to include a molded plastic support member  54  to which is attached an elastomeric disk  56 . The outer periphery of the elastomeric disk  56  is designed to be somewhat thinner than the portion thereof that is adhered to the support member  54  and is somewhat arcuately shaped to engage the inner wall of the container  12  or the optional liner  30  if one is used. The peripheral edge of disk  56  may be somewhat rounded as on an automobile windshield wiper so as to be able to move well in either an upward or downward direction. Likewise, the portion  58  of the elastomeric disk  56  is also made thinner and curved so as to engage the outer wall of the tube  34  with a wiping action. The choice of materials for the plunger&#39;s elastomeric disk  56  may depend on its wear properties as well as the composition of the liquid to be sprayed so that there will be chemical compatibility. 
         [0027]    When the nipple  49  of the adapter  40  is coupled by tubing to an air outlet port  74  or  75  of the spray gun  53  and a quick-connect fitting  59  is connected to the liquid inlet connection  55  of the spray gun for which the adapter has been designed, and the trigger  57  of the spray gun is squeezed, air under pressure is made to flow through the lumen  46  in the adapter and the bore  36  in the cover member  20  to develop or maintain a positive pressure on the upper surface of the plunger  52 . This will urge the plunger  52  to slide down along the tube  34  and, in doing so, will force the paint in the cup  12  up through the filter  35  and the lumen of the tube  34 , through the dome of the cover  20  and up through the lumen  42  of the adapter and from there into the spray gun. A one-way check valve can be used in the tubing between nipple  49  and port  74  or  75  on the gun to maintain pressure in the cup for most consistent spraying as the gun is triggered and released, or as the compressed air supply to the gun is removed and reapplied. Note also that port  51  exists to cover member  20  to allow a pressure relief device to be used to limit pressure in the cup assembly. 
         [0028]    Turning next to  FIG. 2 , the exploded view of the embodiment of  FIGS. 1   a - 1   c  enables one to see the individual parts thereof. 
         [0029]      FIG. 2  also shows with greater clarity the manner in which the elastomeric disk  56  is joined to the support member  54  and the way in which the elastomeric disk  56  is arranged to wipe against the tube  34  as the plunger member  52  is made to descend. It should be noted that the space above the inner curved portion of the elastomeric disk where it seals to the outer diameter of the tube  34  is exposed to air pressure above the plunger  52  to thereby provide a pressure-activated seal to the tube  34 . Other seal arrangements in this area can also be made. 
         [0030]    Formed on the upper surface of the disk  56  is a concentric annular protrusion  65  ( FIG. 2 ) designed to engage and grip the peripheral edge of the support member  54 . A similar protrusion  61  engages the support member  54  proximate its center opening. 
         [0031]    Also seen in  FIG. 2  is a seal ring  63  that fits between the adapter  40  and the central stem of the cover  20  to preclude leakage at the joint between the two. 
         [0032]    In an alternative embodiment, the liner  30  in  FIG. 1   a  is absent. That is, the liner  30  is not essential, but the use thereof is a convenience that eliminates the necessity of cleaning the cup member  12  following each use thereof The liner can simply be discarded. 
         [0033]      FIG. 1   a  shows the liquid cup attachment for the spray gun where the plunger assembly  52  is elevated and the cup  12  is filled with paint or other liquid  67  to be dispensed via a spray gun. In  FIG. 1   b,  air pressure exerted on the upper surface of the plunger  52  has forced it down to a midway position in the cup  12 , causing the paint to flow up through the lumen of the tube  34  and to thereby enter the spray gun where it mixes with the air stream to form an aerosol spray.  FIG. 1   c  shows the plunger fully displaced. 
         [0034]    To displace the air present between the upper paint surface  69  and the bottom of the plunger  52  as seen in  FIG. 1   a,  once the cup is coupled to a spray gun  53 , the operator need only invert the gun and cup so the bottom of the cup is pointed upwards and pull the gun&#39;s trigger  57  to move the plunger and force the air from the cup through the same passage as the paint will eventually flow. 
         [0035]    Once the plunger has reached the bottom of its stroke as seen in  FIG. 1   c.  to cause it to again rise, the operator need only disconnect the air tube (not shown) used to connect the compressed air source to the port  49 , unscrew the air cap ring  73  slightly so the nozzle  70  is recessed within the air cap  76  and cover the spray gun&#39;s air outlet orifices in the cap  73  as the trigger is pulled. This causes the compressed air from the inlet of the gun to be diverted down the lumen of the tube  34  which pressurizes the underside of the plunger, causing it to move upward toward the top member. As seen in  FIG. 1   b,  the support member  54  has a tubular stem portion  72  whose height dimension is selected to provide a positive stop, preventing the elastomeric disk  56  from rising above the level of the cup&#39;s rim  16 . As illustrated, the stem portion  72  will engage the cover&#39;s undersurface to prevent further upward rise of the plunger, maintaining the elastomeric disk  56  below the rim  16 . The procedure may also be used with a partially filled container ( FIG. 1   b ) to return the plunger to its topmost position so that the cup can be removed and the remaining contents emptied into a paint storage bucket. 
         [0036]    If the cup is fabricated from a metal, such as aluminum or stainless steel such that the level of the contents remaining in the cup cannot be directly viewed, an indication of remaining liquid can be obtained by providing a graduated “dip-stick” that is attached to and moves with the support member  54  and that passes through a fluid-type diaphragm seal in the cover  20 . 
         [0037]    Those skilled in the art will appreciate that, with the arrangement disclosed in  FIGS. 1(   a ) through  1 ( c ), the spray gun with the container attached can be held in any of a number of orientations with the base of the container pointed upward, downward or to the side during a spraying operation. Moreover, because the plunger forms an effective seal with respect to the container sidewall and the tubular member  34 , the inside of the cover is not exposed to paint which facilitates clean-up following use. 
         [0038]    This invention has been described herein in considerable detail in order to comply with the patent statutes and to provide those skilled in the art with the information needed to apply the novel principles and to construct and use such specialized components as are required. However, it is to be understood that the invention can be carried out by specifically different equipment and devices, and that various modifications, both as to the equipment and operating procedures, can be accomplished without departing from the scope of the invention itself. For example, and without limitation, the cup can be replaced with a larger capacity container, such as a five gallon pressure pot, that would be connected with a length of hose to the hand-held spray gun liquid inlets and where a suitably designed air-pressure actuated plunger is provided that is made to slide down a tubular support in the pressure pot while wiping the interior wall of the pressure pot.