Abstract:
A dishwasher includes a pump assembly having a multi-stage filtering arrangement which functions to trap soil particles contained in a washing fluid to reduce the number of fresh water fills required to perform a washing operation. All of the washing fluid is initially directed over a filter plate. A first portion of the washing fluid passes the filter plate into a pumping chamber, while a second, soil laden portion, enters a first filter chamber. The second portion is then directed through a medium filter into the intake chamber. The filtered washing fluid is pumped through a conduit to wash arms that spray the washing fluid onto kitchenware. The conduit includes a sampling port which directs a portion of the washing fluid to a second filtering compartment having a fine mesh screen. At the end of the washing operation, the washing water, along with the soil is expelled from the dishwasher.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention pertains to the art of dishwashers and, more particularly, to a pump and filtration system employed in a dishwasher.  
         [0003]     2. Discussion of the Prior Art  
         [0004]     In a typical dishwasher, washing fluid is pumped from a sump into upper and lower wash arms such that kitchenware retained on vertically spaced racks within a tub of the dishwasher will be sprayed with the washing fluid for cleaning purposes. The washing fluid is heated, filtered and recirculated. Prior to recirculating the washing fluid, the fluid is directed through one or more filters to remove soil from the fluid, with the soil being collected in a chamber. Periodically, the system will be purged in order to drain the collection chamber of the soil.  
         [0005]     In recent years, it has become increasingly common to provide a series of straining or filtering units in connection with an overall dishwasher pumping system such that different sized soil particles are collected at varying locations. For example, a strainer can be employed to retain large soil particles, while a fine filter can be utilized to remove smaller particles. That is, the smaller particles are able to pass through the strainer, which essentially constitutes a first filtering unit, and are caught by the second or fine filter. In connection with the pumping and filtering operation, it is also known to incorporate a mincer or chopper in order to minimize soil particle size, such as just prior to a drainage operation.  
         [0006]     Obviously, the ability of the dishwasher to thoroughly clean the kitchenware will depend on a number of factors, including the actual configuration and flow of fluid through the filtering system, as well as the manner in which pumping and draining operations are performed. Although various dishwasher pump and filtration systems are known in the art, there still exists a need for improvements in this field in order to further enhance the overall cleaning functions performed by dishwashers.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention is directed to a pump and filtration system for a dishwasher. In accordance with a preferred embodiment of the invention, an overall dishwasher pump system includes two separate pumps, one for providing a recirculation flow of washing fluid and the other being utilized during draining or purging operations. Most preferably, all of the washing fluid to be recirculated flows over a filter plate arranged in bottom wall of a washing chamber which allows a first portion of the washing fluid to enter a recirculation pump. A second portion of the washing fluid is directed over the filter plate, carrying soil particles too large to pass through the filter plate, into a first filter chamber.  
         [0008]     In accordance with a preferred form of the invention, the first filter chamber includes a substantially cylindrical filter provided with a medium mesh filtering screen for entrapping soil particles from the washing fluid, while permitting cleansed washing fluid to be directed, radially outward into the washing chamber. With this arrangement, the first and second portions of washing fluid inter-mix in the washing chamber and are thereafter directed to a pumping chamber portion of a pump housing. The recirculation pump directs the washing fluid to upper and lower wash arms for spraying onto kitchenware being washed in the dishwasher. More specifically, a portion of the washing fluid is passed through a conduit leading from the pump housing to the lower wash arm. This conduit includes a sampling port for directing a portion of the washing fluid into a second or fine filter chamber. The second filter chamber includes a top wall or cover having a plurality of openings provided with a fine mesh filtering screen for entrapping soil particles while, at the same time, permitting cleansed washing fluid to be directed back into the washing chamber. With this arrangement the washing fluid undergoes a three stage filtering process which enables the dishwasher to perform a washing operation to minimize the need for multiple fills of fresh clean water.  
         [0009]     In further accordance with the most preferred embodiment, the first filter chamber includes a passage that directs the soil trapped by the medium mesh filtering screen to a soil collection chamber. Likewise, the second filter chamber includes a fine particle soil collection compartment provided with a spring biased valve that, during a drain operation, opens into the soil collection chamber. Actually, the soil collection chamber is a first portion of an overall drain chamber including a soil collection portion, a chopping portion and a drain pump.  
         [0010]     At selected times during the washing operation, a drain operation is indicated. At such times, a drain pump is activated to withdraw washing fluid from the dishwasher to a drain. When the drain pump is activated, pump pressure opens the spring biased valve, thereby causing the soil collected in the fine particle soil collection compartment to drop into the soil collection chamber. The soil from the fine soil collection compartment mixes with the soil in the soil collection chamber and is then passed through a chopper plate that minces the soil into even finer particles. These finer particles, in combination with the washing fluid, are then directed to the drain. With this arrangement, soil accumulated during the dishwashing operation is expelled from the dishwasher in such a manner as to prevent a clog from forming in the drain.  
         [0011]     Additional objects, features and advantages of the present invention will become more readily apparent from the following detailed description of a preferred embodiment when taken in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is an upper right perspective view of a dishwasher constructed in accordance with the present invention, with a door of the dishwasher being open;  
         [0013]      FIG. 2  is a perspective view of an overall pump and filtration system incorporated in the dishwasher of the invention;  
         [0014]      FIG. 3  is an enlarged, partial perspective view of the pump and filtration system as viewed through the open door;  
         [0015]      FIG. 4  is a partial, cross-sectional view of the pump and filtration system;  
         [0016]      FIG. 5  is an enlarged partial, cross-sectional view illustrating a portion of the pump and filtration system of  FIG. 4 ;  
         [0017]      FIG. 6  is an upper perspective view of a pump housing constructed in accordance with the present invention;  
         [0018]      FIG. 7  is a lower perspective view of the pump housing of  FIG. 6 ;  
         [0019]      FIG. 8  is a lower perspective view of a flow plate employed with the present invention; and  
         [0020]      FIG. 9  is a perspective view of a pump housing integrated into a bottom portion of a dishwasher constructed in accordance with a second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]     With initial reference to  FIG. 1 , a dishwasher constructed in accordance with the present invention is generally indicated at  2 . As shown, dishwasher  2  includes a tub  5  which is preferably injection molded of plastic so as to include integral bottom, side, rear and top walls  8 - 12  respectively. Within the confines of walls  8 - 12 , tub  5  defines a washing chamber  14  within which soiled kitchenware is adapted to be placed upon shiftable upper and lower racks (not shown), with the kitchenware being cleaned during a washing operation in a manner widely known in the art. Tub  5  has attached thereto a frontal frame  16  which pivotally supports a door  20  used to seal washing chamber  14  during the washing operation. In connection with the washing operation, door  20  is preferably provided with a detergent tray assembly  23  within which a consumer can place liquid or particulate washing detergent that is dispensed at predetermined portions of a wash cycle. Of course, dispensing detergent in this fashion is known in the art such that this arrangement is only being described for the sake of completeness.  
         [0022]     Arranged within tub  5  and, more specifically, mounted within a central opening  27  formed in bottom wall  8 , is a pump and filtration assembly  30 . In the preferred embodiment shown in  FIGS. 1-3 , pump and filtration assembly  30  includes a filter housing  33 , an annular outer radial outermost strainer  36 , and an annular inner radial or course strainer  39 . A detailed description of the exact structure and operation of pump and filtration assembly  30  will be described more fully below. For the sake of completeness, extending about a frontal portion of pump and filtration assembly  30 , at a position raised above bottom wall  8 , is a heating element  44 . Heating element  44  preferably takes the form of a sheathed, electric resistance-type heating element of a type commonly found in household dishwashers.  
         [0023]     In general, pump and filtration assembly  30  is adapted to direct washing fluid to at least a lower wash arm  47  and a supply conduit  51 . As depicted, supply conduit  51  includes a substantially horizontal lower section  53  extending away from filter housing  33  of pump and filtration assembly  30 , a vertical section  54  which generally extends along rear wall  11 , and a generally horizontally extending upper section  55  ( FIG. 2 ) which rotatably supports an upper wash arm  59 . Vertical section  54  has attached thereto a wash fluid diverter or manifold  66  which defines upper and lower ports  68  and  69 .  
         [0024]     Although not considered part of the present invention, each of upper and lower ports  68  and  69  has associated therewith a valve, such as a flapper element indicated at  72 , for preventing any water flowing through supply conduit  51  from exiting either port  68  or  69  unless structure is inserted into a respective port  68 ,  69  so as to deflect a respective flapper element  72 . In general, wash fluid diverter  66  can actually be formed with a varying number of ports ranging from 1 to 3 or more. Wash fluid diverter  66  illustrated in  FIG. 2  is actually designed to cooperate with a vertically adjustable upper rack (not shown) which carries an associated underside wash arm and respective piping that becomes aligned with and projects into a respective port  68 ,  69  in order to deflect flapper element  72 . In this manner, an additional wash arm is provided to spray washing fluid upon kitchenware, thereby supplementing lower wash arm  47  and upper wash arm  59  during a washing operation within dishwasher  2 . In general, vertically adjustable racks, as well as multi-port wash fluid diverters are known in the art such that this structure will not be described further here.  
         [0025]     Pump and filtration assembly  30  has associated therewith a drain pump  79  (see  FIGS. 3 and 4 ) supported in part beneath bottom wall  8  of tub  5  through a suspension bracket  82 . Drain pump  79  has associated therewith a drain hose  85  (see  FIG. 1 ) including at least one corrugated or otherwise flexible curved portion  89  that extends about an arcuate hanger  92  provided on an outside surface of side wall  10 . Drain hose  85  is also preferably secured to tub  5  through various clips, such as that indicated at  95 . In any event, in this manner, an upper loop is maintained in drain hose  85  to assure proper drainage in a manner known in the art.  
         [0026]     Particular reference will now be made to  FIGS. 4-8  in describing further details of pump and filtration assembly  30 , as well as other components of dishwasher  2 . As best shown in  FIG. 4 , bottom wall  8  extends to a support flange  121 . Support flange  121  is provided to support an outer peripheral edge portion (not separately labeled) of outermost strainer  36 . Support flange  121  leads to a central trough  129  that slopes downward toward pump and filtration assembly  30 .  
         [0027]     In accordance with a preferred embodiment of the present invention, pump and filtration assembly  30  includes a housing  140  having a central recessed section  142  and an outer edge  144  that is adapted to engage with flange  121  through a plurality of L-shaped projections  145   a - d  (see  FIGS. 5 and 6 ). As best seen in  FIG. 6 , housing  140  includes a downward sloping upper portion  147  that leads to a lower portion or bottom plate  148 . Preferably, formed within lower portion  148  is a washing fluid collection reservoir or pumping chamber  154 . In accordance with the most preferred form of the invention, pumping chamber  154  includes a recirculation portion  157  and a discharge/drain portion  158 . More specifically, recirculation portion  157  is divided into an inlet passage  159  and an outlet or recirculation passage  160 . Preferably, inlet passage  159  and recirculation passage  160  are arranged substantially parallel to one another and extend from outer edge  144  radially inward toward a central portion (not separately labeled) of housing  140 . In general, recirculation portion  157  and drain portion  158  extend radially inward from outer edge  144  towards the central portion of housing  140  and interconnect through a passage  164 . In accordance with the invention, a flapper valve  165  (not shown in  FIG. 6  for clarity, but depicted in  FIG. 4 ) is arranged at passage  164  to prevent washing fluid from passing from drain portion  158  to recirculation portion  157  prior to the activation of drain pump  79 .  
         [0028]     In accordance with a preferred embodiment of the present invention, housing  140  is formed from a single or one-piece injection molded plastic unit (see  FIGS. 6 and 7 ) which facilitates both the manufacturing and the mounting of housing  140  to bottom wall  8  of dishwasher  2 . However, in accordance with another embodiment illustrated in  FIG. 9 , a corresponding housing  140 ′ is actually integrally formed, such as by injection molding, with bottom wall  8  of tub  5 .  
         [0029]     Referring back to  FIGS. 5 and 6 , drain portion  158  terminates in a drain pump mount/receiver  166 . As best shown in  FIG. 5 , drain pump mount  166  includes an outer lip portion  168  adapted to receive a mounting plate  170  of drain pump  79 . Outer lip portion  168  leads to a first upright wall portion  172  which actually serves as an end stop or sealing portion for mounting plate  170 . Extending from first upright wall portion  172  is an intermediate wall portion  174  that defines an impeller chamber  176  having arranged therein an impeller  177  of drain pump  79 . Impeller  177  is driven by a pump motor (not separately labeled) to draw washing fluid in from pump and filtration assembly  30  to be directed to drain hose  85 . In any event, intermediate wall portion  174  leads to a second upright wall section  178  that separates a collection chamber  182  from impeller chamber  176 . In addition, second upright wall section  178  serves as a mounting surface for a chopper plate  188  having a plurality of apertures  189 . Actually, a chopper  190 , driven by impeller  177 , rotates adjacent chopper plate  188 , dicing and chopping food particles trapped within collection chamber  182  prior to their release to drain hose  85 . Further illustrated in  FIG. 5 , a conduit  194  extends from an upper portion of impeller chamber  176 . With this arrangement, impeller  177  directs a portion of the drain flow upward which, as will be detailed more fully below, operates a mechanism for draining collected fine particles.  
         [0030]     In further accordance with the preferred form of the present invention, inlet passage  159  and recirculation passage  160  of recirculation portion  157  collectively terminate in a recirculation pump mount  204  (particularly see  FIGS. 4 and 6 ). As shown, recirculation pump mount  204  is arranged substantially opposite drain pump mount  166 . Recirculation pump mount  204  is adapted to receive a recirculation pump  206 . Toward that end, recirculation pump mount  204  includes an outer rim portion  208  adapted to support recirculation pump  206  which, in turn, includes a housing  207  that includes a combination inlet/outlet conduit  210 . In accordance with the most preferred form of the invention, inlet/outlet inlet/outlet conduit  210  is secured within recirculation pump mount  204  through a gasket  212 . Gasket  212  establishes a seal and is provided to minimize the effects of vibration and noise in dishwasher  2 . Preferably, gasket  212  is formed from a resilient, elastomeric material that absorbs the various vibrations created by the operation of recirculation pump  206 . As best seen in  FIGS. 4 and 6 , inlet/outlet conduit  210  includes a central inlet portion  216  and an outer sleeve or outlet portion  220 . In accordance with the most preferred embodiment, outlet portion  220  is positioned radially about inlet portion  216 . With this arrangement, washing fluid is drawn through an inlet section  223  of pump mount  204  and guided into inlet portion  216  of recirculation pump  206 . The washing fluid is then drawn passed an impeller  221  that redirects the washing fluid outward through a plurality of directional vanes  224  to outlet portion  220 . In the most preferred form of the invention, inlet  216  and outlet  220  are arranged concentrically such that fluid flow reverses direction approximately 180° within inlet/outlet conduit  210  while still flowing coaxially. The washing fluid then travels into a recirculation portion  225  of recirculation pump mount  204 , which leads to recirculation passage  160  of housing  140 .  
         [0031]     In further accordance with the present invention, arranged within lower portion  148  of housing  140  is a flow or suction plate  240 . Referring to  FIG. 8 , flow plate  240  includes a base portion  245  having a first opening  247  adapted to be positioned above collection chamber  182  (see  FIG. 4 ) and a second opening  248  adapted to be positioned above recirculation passage  160  ( FIG. 6 ). Arranged about base portion  245  are a plurality of apertures  250 - 253  which are positioned to correspond with an associated plurality of mounting bosses  255 - 258  (see  FIG. 6 ) that project from lower portion  148  of housing  140 . With this arrangement, flow plate  240  is removably secured to housing  140  through a plurality of mechanical fasteners (not shown) that extend through apertures  250 - 253  and engage into mounting bosses  255 - 258 . Flow plate  240  is also provided with a plurality of raised wall portions, indicated generally at  262 . Raised wall portions  262  nest with corresponding structure, indicated generally at  263  in  FIG. 6 , to define an inlet section  264  and a recirculation section  265 . Actually, inlet section  264  and recirculation section  265  respectively correspond to inlet and recirculation passages  159  and  160  of housing  140 . In addition, flow plate  240  is provided with a supply conduit  270  that extends from a first end  273 , which is open to recirculation section  265 , to a second end  274  adapted to interconnect with lower section  53  of supply conduit  51  (see  FIG. 2 ). With this particular arrangement, a portion of the washing fluid being redirected or recirculated from recirculation pump  206  is directed upwardly through opening  273  in supply conduit  270  toward upper wash arm  59  and wash fluid diverter  66 , while a separate portion of washing fluid is directed from second opening  248  into lower wash arm  47 .  
         [0032]     Referring back to  FIGS. 4 and 5 , arranged above flow plate  240  is a first filter chamber  288 . As shown, first filter chamber  288  includes a base portion  290  having an opening  291  positioned above both first opening  247  of flow plate  240  and collection chamber  182 . Base portion  290  extends to an upstanding wall portion  292  which, in accordance with the most preferred form of the present invention, includes a filter screen  293 . Actually, first filter chamber  288  is fluidly connected to radial, coarse strainer  39  such that water and soil particles traveling over radial outermost strainer  36  enter through strainer  39  and are directed to first filter chamber  288 . As will be detailed more fully below, soil and other entrapped particles are carried from filter chamber  228  to soil collection chamber  182 , while the washing fluid is directed radially outwardly through filter  293  back to tub  5 .  
         [0033]     Arranged above first filter chamber  288  is a second or fine filter chamber  296 . Second or fine filter chamber  296  includes a base portion  298  that extends to a side wall  299  and a cover  300 . Preferably, cover  300  is provided with a plurality of enlarged openings  301 . As best illustrated in  FIGS. 4 and 5 , each of enlarged openings  301  has associated therewith a fine mesh screen  302 , preferably having openings in the order of 75 microns to 3 mils, for filtering purposes. Cover  300  is also supports structure that rotatably positions lower wash arm  47  above filter housing  33  as will be discussed more fully below.  
         [0034]     In further accordance with the most preferred form of the invention, second or fine filter chamber  296  is provided with a fine particle collection chamber  308  for collecting fine soil particles entrapped within fine filter chamber  296 . Preferably, fine particle collection chamber  308  is provided with a pivoting cover  310  (see  FIG. 5 ) having a seal or gasket  311 . More preferably, cover  310  is pivotally connected to a pivot arm  313  that interconnects cover  310  with a piston  315 . As shown, piston  315  is provided with a face portion  317  that extends to a plunger  318  about which is a positioned a spring  319 . During a wash cycle, spring  319  maintains cover  310  in a closed position, thereby allowing fine soil particles to accumulate in fine particle collection chamber  308 . However, during a drain operation, impeller  177  of drain pump  79  generates a fluid force through conduit  194  that impinges upon face portion  317  of piston  315 . At this point, piston  315  is forced upward against the biasing force of spring  319  in order to pivot arm  313  and open cover  310 . As fine particle collection chamber  308  is positioned above collection chamber  182 , fine soil particles contained within collection chamber  308  pass from fine filter chamber  296  into collection chamber  182  to be directed to drain hose  85 .  
         [0035]     Referring to  FIG. 4 , extending through central opening  304  in cover  300  is a central hub portion  334  having arranged thereon a plurality of bearings or the like (not shown) for rotatably supporting lower wash arm  47 . Preferably, central hub  334  is in fluid communication with second opening  248  of flow plate  240  through a conduit  337 . With this arrangement, a portion of the washing fluid being directed from recirculation pump  206  travels through conduit  337  into lower wash arm  47  and is thereafter directed upward onto kitchenware within dishwasher  2 . However, prior to entering lower wash arm  47 , conduit  337  is formed with a sampling port  340  which opens into second filter chamber  296 .  
         [0036]     The manner in which fluid and entrapped particles flow through pump and filtration assembly  30  during operation of dishwasher  2  will now be described. In a manner known in the art, tub  5  will be initially, partially filled with water which can be further heated by activation of heating element  44 . During a washing cycle, recirculation pump  206  is operated to concurrently draw in washing fluid from tub  5  and thereafter redirect or recirculate the washing fluid to the various wash arms  47  and  59 , as well as wash fluid diverter  66 . The spraying of the washing fluid will cause food particles to fall from kitchenware placed in dishwasher  2 , while the washing fluid with entrained particles will fall onto bottom wall  8 . Initially, a portion of the washing fluid will pass through outermost strainer  36  into central trough  129 . This portion of the washing fluid will then pass into upper portion  147  of filter housing  140  and thereafter be directed under flow plate  240  into pumping chamber  154 .  
         [0037]     A second portion of the washing fluid, as well as soil particles too large to pass through outermost strainer  36 , is directed into coarse strainer  39 . Coarse strainer  39  leads to first filter chamber  288  such that, as the fluid and particles enter first filter chamber  288 , the washing fluid is directed radially outwardly through annular filter  293  into upper portion  147  of filter housing  140 . Soil particles too large to pass through filter  293  settle to base portion  290  of filter chamber  288  and eventually are collected within soil collection chamber  182  to be eventually chopped and directed to drain hose  85 .  
         [0038]     The washing fluid passing into upper portion  147  of housing  140 , whether originating from filter chamber  288  or from central trough  129 , is guided under flow plate  240  into recirculation portion  157 . The washing fluid is actually drawn in through inlet passage  159  and guided to inlet section  223  of recirculation pump mount  204 . Due to the presence of flapper valve  165  in passage  164 , only fluid contained in recirculation portion  157  is directed into pump  206 . The washing fluid then flows into recirculation pump  206  through combination inlet/outlet inlet/outlet conduit  210 , passed impeller  221  and is redirected through directional vanes  224  to outlet portion  220  and finally into recirculation passage  160 . With this arrangement, a first portion of the washing fluid is diverted to conduit  51  through supply conduit  270 . This first portion of the washing fluid is guided to upper wash arm  59 , as well as wash fluid diverter  66  and eventually back onto bottom wall  8  of tub  5 . A second portion of the washing fluid is guided into second opening  248  in flow plate  240 , through conduit  337  toward lower wash arm  47 . The washing fluid flowing into lower wash arm  47  will be sprayed upward into tub  5  through nozzles (not separately labeled) provided on lower wash arm  47  in order to direct the fluid upwardly against kitchenware supported upon a lower rack (not shown), and downward as will be discussed more fully below.  
         [0039]     With respect to the fluid flowing through conduit  337 , a small percentage of this fluid will enter sampling port  340  so as to be directed into second or fine filtering chamber  296 . The portion of the fluid that flows into filter chamber  296  will actually be forced to flow around filter chamber  296  to fine particle collection chamber  308 . When drain pump  79  is not activated, this fluid and entrained particles can only initially fill up filter chamber  296  and fine particle collection chamber  308 . Once chambers  296  and  308  are filled, the fluid will be caused to flow out of filter housing  33  and back into tub  5  through the various enlarged openings  301  provided with fine mesh screen  302 . Of course, given the presence of fine mesh screen  302 , the fluid re-entering tub  5  from filter chamber  296  will be substantially cleansed of any soil having any substantial particulate size. Any soil particles which are larger than that which can flow through screen  302  will be forced to remain within filter chamber  296  and actually find their way into fine particle collection chamber  308  due to both the current flow created by incoming fluid into filter chamber  296  through sampling port  340  and gravity. The cleansed washing fluid will be mixed with the remaining fluid in tub  5  and, in fact, re-mixed with the recirculated fluid flowing out at least lower wash arm  47  and upper wash arm  59 .  
         [0040]     With this arrangement, continued recirculation of the washing fluid will assure that most, if not all, of the soil particles will be entrapped and eventually directed to collection chamber  182 . Furthermore, by continuing to provide a flow into sampling port  340  and further finely filtering particles entrained in this fluid by means of fine mesh screen  302 , the percentage of soil in the recirculated washing fluid actually becomes quite small. Of course, soil will be accumulating within collection chambers  182  and  308 , along with a certain percentage in filter chambers  288  and  296 . Furthermore, since the fluid is attempting to exit pump and filtration assembly  30  through fine mesh screen  302 , the underside of fine mesh screen  302  itself will actually start to accumulate soil and can become clogged. For this purpose, lower wash arm  47  is provided with one or more lower nozzles (not shown) in order to direct a spray of washing fluid downward onto fine mesh screen  302 . Therefore, this directed flow will tend to wash particles off fine mesh screen  302  and back into filter chamber  296  and, eventually, to fine particle collection chamber  308 .  
         [0041]     In accordance with the most preferred embodiment of the present invention, complete drainage operations are performed on a preprogrammed, timed basis. However, additional drain or purging operations can also be performed. In accordance with the invention, an initial drainage sequence is established depending on the dishwashing operation set by the user. For instance, if the user selects a normal wash mode, a fill operation will be performed wherein a certain amount of water, which will vary with dishwasher models (generally in the order to 6.8-8 quarts), is introduced into tub  5 . Thereafter, a main wash cycle will be entered. In accordance with the most preferred form of the invention, the main wash cycle is set at 34 minutes. The main wash cycle is then followed by a rinse cycle lasting approximately 25 minutes. Thereafter, a 30 minute dry cycle is entered.  
         [0042]     In the alternative, the user can select a dirty wash cycle which would result, for example, in an 8 minute pre-wash, followed by a 28 minute main wash cycle, a pre-rinse of approximately 10 minutes, a main rinse of approximately 25 minutes, and then a 30 minute drying period. With these configurations, the normal and dirty wash cycles would have 2 or 4 fill periods respectively. Correspondingly, there would be 2 or 4 drain operations performed, each being approximately 2 minutes in duration. Therefore, the drainage operations are pre-programmed based on the particular washing cycle selected, i.e., provided at specific lapsed time periods during an overall dishwashing operation.  
         [0043]     In any case, during full or partial drainage operations, soil will be removed from collection chamber  182  and fine particle collection chamber  308  when a combination of soil and washing fluid will be directed, through the operation of drain pump  79 , into drain hose  85 . However, prior to passing into drain hose  85 , the soil and washing fluid is directed passed chopper blade  190  which minces, and finely chops any large soil particles contained within the washing fluid prior to their passing through apertures  189  in chopper plate  188 . Once the soil particles are chopped to a size such that they can pass through apertures  189 , drain pump  79  directs the washing fluid and entrained soil particles to drain hose  85 .  
         [0044]     During the operation of drain pump  79 , flapper valve  165  arranged within passage  164  is forced open by the direction of washing fluid established by drain pump  79 . In this manner, any washing fluid and entrained particles contained within recirculation portion  157  of pumping chamber  154  are directed passed chopper plate  188  to drain hose  85 . In addition, the force generated by impeller  177  of drain pump  79  forces fluid upwardly into conduit  194 , wherein the fluid impinges upon face portion  317  of piston  315 . As discussed above, the force of the washing fluid directed upon piston  315  causes pivot arm  313  to open cover  310 , thereby enabling fine particles collected within fine particle collection chamber  308  to fall, under the force of gravity, into collection chamber  182 . With this particular arrangement, during each drain operation, soil particles contained within each of the filter chambers, as well as the pumping portion of housing  140 , are directed from dishwasher  2  into drain hose  85 .  
         [0045]     Although described with reference to a preferred embodiment of the present invention, it should be readily apparent to one of ordinary skill in the art that various changes and/or modifications can be made to the invention without departing from the spirit thereof. For instance, although fine mesh screen  302  is back washed through the operation of lower wash arm  47 , it may occur that the fine mesh screen becomes clogged to a point that the back washing will no longer alleviate the problem. Toward that end, either a pressure release or overflow system can be provided in connection with second filter chamber  296  in order to alleviate this problem. In any event, the above arrangement provides for an extremely compact multi-stage filtering and pump system enabling a recirculation pump to be simultaneously interconnected to inlet and outlet flow portions in a quick and convenient manner. In any event, it should be understood that the invention is only intended to be limited to the scope of the following claims.