Abstract:
A dishwasher includes a pump assembly which functions to chop all fluid entrained soil prior to directing fluid to upper and lower wash arms. A flow conduit leading to the upper wash arm is provided with a sampling port which directs a percentage of the fluid flow into a filter chamber having one or more fine mesh filter screens that open into the dishwasher tub basin. The filter chamber is exposed to a collection chamber that leads to a flapper valve and then to a drain port. A sealing chamber joins the filter chamber with the collection chamber. A sealing member is positioned in the sealing chamber to selectively seal the filter chamber after a portion of the fluid is drained. Once sealed, a drain pump expels the fluid from the washing tub. After the tub is empty, the remainder of the fluid is drained from the filter chamber.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application represents a continuation-in-part of U.S. patent application Ser. No. 10/186,739 entitled “DISHWASHER PUMP AND FILTRATION SYSTEM” filed Jul. 2, 2002, now U.S. Pat. No. 7,146,992 well as a continuation-in-part of U.S. patent application Ser. No. 10/186,714 entitled “METHOD OF OPERATING A DISHWASHER PUMP AND FILTRATION SYSTEM” filed Jul. 2, 2002, now U.S. Pat. No. 6,811,617. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention pertains to the art of dishwashers and, more particularly, to a pump and drain system employed in a dishwasher. 
     2. Discussion of the Prior Art 
     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. 
     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. 
     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 
     The present invention is directed to a pump and filtration system in 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 past a radial strainer, through a generally U-shaped inlet trap and then to an impeller of the recirculation pump through a chopper blade and apertured plate arrangement. In this manner, any large particles are prevented from passing through the strainer, while the remainder of the fluid entrained particles are forced through the chopper blade and plate arrangement prior to reaching the impeller of the recirculation pump. 
     The impeller directs the recirculating fluid radially outwardly, then the fluid is forced to flow through an involute manifold. At the manifold, the recirculating fluid is directed radially inwardly and then up to respective upper and lower wash arms. A flow conduit leading to the upper wash arm is provided with a sampling port which directs a percentage of the fluid flow into a filter chamber. The upper wall or top of the filter chamber is generally defined by one or more fine mesh filter screens that open into the dishwasher tub basin. At one annular position about the filter chamber is provided a collection chamber that leads to a flapper valve and then to a drain port. The drain port is connected to an inlet of the drain pump. With this arrangement, a percentage of the recirculating fluid flow is directed through the sampling port wherein any particles therein will settle in the collection chamber. Fluid in the filter chamber is permitted to flow upwardly through the fine mesh filter screen(s). Periodically, at timed intervals, drainage operations are performed to purge the collection chamber. 
     In one preferred form of the invention, an overflow tube, which is in fluid communication with the filter chamber, extends upwardly along the rear wall of the tub basin. When the fine mesh filter becomes clogged, fluid will be forced to flow up the overflow tube. A separate filter is provided within a housing atop the tube in order to prevent soiled fluid from the filter chamber reaching the tub basin through the overflow tube. In this manner, the recirculated fluid can continue to be filtered, even while the fine mesh filter is clogged, until a timed drainage operation is performed. 
     In further accordance with one preferred embodiment of the present invention, a filter guard is secured to the housing of the recirculation pump, with the filter guard extending over portions of the fine mesh filter. More specifically, the filter guard is mounted directly above the fine filter and has an outer wall which is angled to protect or shield the fine filter from damage, such as from utensils or the like falling thereon within the tub basin, as well as visually obscuring the fine filter. The filter guard preferably has a curved underside for directing downward sprays from the lower wash arm onto the fine filter in order to backwash the fine filter for cleaning purposes. In addition, the filter guard includes wash out areas for flushing out any trapped food particles. 
     In accordance with another preferred embodiment of the present invention, a sealing chamber is positioned between the filter chamber and the collection chamber. A flapper valve, provided for diverting the flow of washing fluid between the tub and the filter chamber, is positioned between the sealing chamber and the collection chamber. More specifically, the flapper valve includes an upper portion that extends into the sealing chamber, and leg members that extend into the collection chamber. Arranged within the sealing chamber is a check ball that, upon activation of the drain pump, is drawn against the upper portion of the flapper valve. Once the check ball seats against the upper portion of the flapper valve, the filter chamber is closed off from the collection chamber. However, prior to sealing, a portion of the washing fluid and soil particles entrapped in the filter chamber is drawn into the collection chamber as the check ball travels downward. 
     Once sealed, the drain pump creates a suction force that deflects the leg members of the flapper valve inward, thereby opening a passage between the washing chamber and the drain. In this manner, the drain pump directs the washing fluid from the washing chamber into the drain hose. Once the washing chamber is empty, the drain pump begins to ingest air which causes the leg members of the flapper valve to reseat against the collection chamber. At this point, the check ball rises in the sealing chamber, allowing whatever washing fluid and soil particles that remain in the filter chamber to pass to the drain. 
     Additional objects, features and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments when taken in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         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; 
         FIG. 2  is another perspective view of the dishwasher of  FIG. 1  with the door open; 
         FIG. 3  is a perspective view of an overall pump and filtration system incorporated in the dishwasher of the invention; 
         FIG. 4  is an isometric, cross-sectional view through both a tub basin and the overall pump and filtration system of the dishwasher of  FIG. 1 ; 
         FIG. 5  is a perspective, cross-sectional view through the tub basin and the pump/filtration system; 
         FIG. 6  is an elevational, cross-sectional view through the tub basin and the pump/filtration system; 
         FIG. 7  is another elevational, cross-sectional view through the tub basin and the pump/filtration system; 
         FIG. 8  is a perspective view of a flapper valve incorporated in the pump and filtration system of the invention; 
         FIG. 9  is an enlarged, perspective view of the recirculation pump, along with the lower wash arm, shown in the overall system of  FIG. 3 ; 
         FIG. 10  is an upper perspective view of a filter guard shown mounted atop the recirculation pump in  FIG. 9 ; 
         FIG. 11  is a lower perspective view of the filter guard of  FIG. 9 ; 
         FIG. 12  is a perspective view of a modified water conduit and overflow tube arrangement for the dishwasher of  FIG. 1 ; 
         FIG. 13  is a block diagram of a control unit for the dishwasher; and 
         FIG. 14  is a perspective, cross-sectional view through the tub basin and the pump/filtration system illustrating a sealing chamber and check ball arranged in accordance with a second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With initial reference to  FIGS. 1-3 , a dishwasher constructed in accordance with the present invention as generally indicated at  2 . As shown, dishwasher  2  includes a tub  5  which is preferably injection molded of plastic or formed of stainless steel 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 chamber  14  during a 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 for dispensing at predetermined portions of the washing operation. 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. 
     Disposed within tub  5  and, more specifically, mounted within a central opening  27  (see  FIGS. 4-7 ) formed in bottom wall  8  of tub  5 , is a pump assembly  30 . In the preferred embodiment and as illustrated in these figures, pump assembly  30  includes a main housing  33 , an annular, radial outermost strainer  36  and a filter guard  39 . A detailed description of the exact structure and operation of pump assembly  30  will be described more fully below. Extending about a substantial portion of pump assembly  30 , at a position raised above bottom wall  8 , is a heating element  44 . In a manner known in the art, heating element  44  preferably takes the form of a sheath, electric resistance-type heating element. 
     In general, pump assembly  30  is adapted to direct washing fluid to at least a lower wash arm  47  and a conduit  51 . As depicted, conduit  51  includes a substantially horizontal, lower section  53  extending away from main housing  33  of pump assembly  30 , a vertical section  54  which generally extends along rear wall  11 , and a generally horizontally extending upper section  55  which rotatably supports an upper wash arm  59 . Vertical section  54  has attached thereto a wash fluid diverter  66  which defines upper and lower ports  68  and  69 . 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 conduit  51  from exiting either of 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. The overall wash fluid diverter  66  is actually designed to cooperate with a vertically adjustable upper rack (not shown) which would carry an associated underside wash arm and respective piping that would become aligned with and project into a respective port  68 ,  69  in order to deflect flapper element  72  so as to provide an additional wash arm used to further 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. 
     Pump assembly  30  has associated therewith a drain port  76  to which is attached a drain pump  79 . Drain pump  79  is secured beneath bottom wall  8  of tub  5  through the use of a suspension bracket  82 . Drain pump  79  has associated therewith a drain hose  85  including at least one corrugated or otherwise 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. 
     Also projecting from main housing  33  of pump assembly  30  is an overflow tube  98 . More specifically, overflow tube  98  includes a first end  99  leading from main housing  33  in a manner which will be detailed more fully below, as well as a second end  100  which leads into an overflow housing  104 . In accordance with the preferred embodiment shown in these drawings, overflow tube  98  is preferably integrated into conduit  51  during manufacturing, such as through a blow molding or extrusion operation. In any event, second end  100  of overflow tube  98  leads out of the overall structure defining conduit  51  to direct fluid from within overflow tube  98  into overflow housing  104 . Overflow housing  104  incorporates a coarse filter  106 . In one preferred embodiment, filter  106  has openings in the order of 20 mils. Although a removable cover could be provided to access filter  106  for replacement/cleaning purposes, filter  106  is preferably molded into housing  104  such that the entire housing/filter unit would be replaced if necessary. However, as will be detailed further below, a backwashing arrangement for filter  106  is preferably employed for cleansing purposes. In any event, further details on the construction and operation of this overflow arrangement will be provided below in describing the overall operation of pump assembly  30 . 
     At this point, reference will now be made to  FIGS. 4-7  in describing further details of pump assembly  30 , as well as other components of dishwasher  2 . As best shown in  FIG. 4 , side walls  9  and  10  lead into bottom wall  8  through a pair of spaced plateau portions  121  and  122 . Rollers for a lower rack (not shown) are adapted to be supported upon plateau portions  121  and  122  for movement of the rack into and out of tub  5 . In any event, bottom wall  8  includes a lower base portion  126  which slopes inwardly towards a trough  129 . Trough  129  defines an inlet trap which is generally U-shaped in cross-section as clearly shown in each of  FIGS. 4-7 . Radially inwardly of trough  129 , bottom wall  8  includes an inner radial plateau portion  132  that leads to a downwardly extending portion  135  and finally a substantially horizontally extending innermost portion  137 . Innermost portion  137  defines central opening  27  within which pump assembly  30  extends as clearly shown in these figures. 
     Pump assembly  30  includes a lower housing plate  145  that includes a central recess section  148  and an outer edge  152 . Spaced slightly inwardly from outer edge  152 , lower housing plate  145  is provided with a lower rib  155 . As shown, lower rib  155  extends into a notch (not labeled) defined in a seal  160 . More specifically, seal  160  is sandwiched between downwardly extending portion  135  and lower rib  155 , while also projecting along outer edge  152 . In this manner, fluid that flows through trough  129  and along inner-radial plateau portion  132  is prevented from reaching innermost portion  137 , but rather is forced to flow above lower housing plate  145 . 
     Pump assembly  30  has associated therewith a motor  165 . In general, motor  165  is of the type known in the art and includes a housing  168  and an associated driveshaft  170  which is rotatably supported by housing  168  through upper and lower bearing units  172  and  173 . Since the general construction and operation of motor  165  is known in the art, it will not be detailed further herein. However, it should be noted that driveshaft  170  is secured for concurrent rotation with a lower drive sleeve  174 , which is spaced from an upper sleeve  175 . Although not shown in detail, lower drive sleeve  174  is preferably formed of two parts which securely sandwiches a chopper blade  178  therebetween. In this manner, chopper blade  178 , which extends substantially parallel to but spaced vertically above lower housing plate  145 , rotates in unison with driveshaft  170  during operation of motor  165 . Arranged above chopper blade  178  is a fixed, apertured plate  182 . As clearly shown in at least  FIGS. 4 and 5 , plate  182  actually includes a plurality of spaced holes  184  which are sized to permit passage of only predetermined sized particles entrained within washing fluid as will be detailed more fully below. 
     At this point, it should be noted that apertured plate  182  is actually secured to an annular rib  186  which projects downward from an intermediate housing plate  189 . Actually, intermediate housing plate  189  has arranged radially outward of annular rib  186  a plurality of annularly spaced bosses, one of which is indicated at  193  in  FIG. 7 , for securing fixed apertured plate  182  in a desired position. Intermediate housing plate  189  also includes a series of upstanding, radially spaced ribs  195 - 197  which project in a direction opposite to annular rib  186 , as well as an additional rib  198  which extends downward from intermediate housing plate  189 . For reasons which will be discussed more fully below, rib  198  actually defines a flow plate which projects into trough  129 . Ribs  196  and  197  extend upwardly substantially parallel to one another and define, in accordance with the present invention, a filter chamber  202 . A cover  204 , which includes a plurality of enlarged openings  206 , spans across ribs  196  and  197 . As best illustrated in  FIGS. 4 and 5 , each of enlarged openings  206  has associated therewith a fine mesh screen  207 , preferably having openings in the order of 75 microns or 3 mils, for filtering purposes. Filter chamber  202  is open, at one side of pump assembly  30 , to a collection chamber  212 . This arrangement is best shown in  FIGS. 4 and 5 , with these figures also indicating the manner in which cover  204  is secured to intermediate housing plate  189  as well as bottom wall  8 . 
     More specifically, cover  204  is provided with various annularly spaced holes, one of which is indicated at  214  aligned with a respective upstanding sleeve  215  projecting up from intermediate housing plate  189 , as well as a respective mounting boss  216  formed integral with bottom wall  8  or integral with lower housing plate  145  (stainless steel tub models). Upon aligning these components in this manner, mechanical fasteners (not shown) are placed through a respective hole  214  and sleeve  215  and secured within respective bosses  216 . In any event, at this point, it is merely important to note that filter chamber  202  extends about a top portion of pump assembly  30  and is in fluid communication with collection chamber  212  which, as will be discussed more fully below, is in fluid communication with drain port  76  and drain pump  79 . 
     With further reference to each of  FIGS. 4-6 , intermediate housing plate  189  locates a pump component indicated at  218 . Rotating with pump component  218  is another pump component or impeller  220 . As shown, impeller  220  is also spaced from upper sleeve  175 . In any event, impeller  220  is drivingly connected to driveshaft  170  so as to rotate in unison with driveshaft  170  and chopper blade  178  during operation of motor  165 . Although further details will be provided below, at this point, it should be noted that components  218  and  220  collectively define a recirculating pump incorporated in the overall pump assembly  30 . 
     In accordance with the most preferred embodiment of the invention, arranged above impeller  220  is a fixed involute manifold  226 . Involute manifold  226  is shown to include a first involute member  228  and a second involute member  232  which are intermeshed in a manner defining a radially spiraling chamber. Second involute member  232  is preferably formed as part of a pump housing cap  235  having an outermost radial portion  239  provided with at least one annular recess  242  into which projects rib  195  of intermediate housing plate  189 . A second annular recess  243  is defined radially outwardly of annular recess  242  as clearly shown in these figures. In any event, it is merely important to note that pump housing cap  235  is fixed to intermediate housing plate  189  with at least the positioning of rib  195  in annular recess  242  creating a seal between these members. In the most preferred form of the invention shown, pump housing cap  235  actually includes an outermost radial portion, i.e., a lower region  239  that defines annular recesses  242  and  243 , an intermediate region  248  defining second involute member  232 , and an upper region  250  provided with a central opening  253 . A shaft  257  which is secured to first involute member  228  extends through both opening  253  and a sleeve  260  formed integral with lower wash arm  47  in order to rotatably support lower wash arm  47 . As also illustrated in these figures, upper region  250  also opens into lower section  53  of conduit  51 . As best shown in  FIG. 7 , prior to vertical section  54 , conduit  51  is formed with a sampling port  267  which opens into a cylinder member  268  formed as part of cover  204 . In turn, cylinder member  268  leads into filter chamber  202 . 
     The manner in which fluid and entrained particles flows through pump 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, motor  165  is activated in order to concurrently rotate chopper blade  178  and impeller  220 . In this manner, the washing fluid with entrained particles will be drawn into trough  129  between fins  200  of strainer  36 . Given the distances between the respective fins  200  of strainer  36 , any large food pieces, utensils or the like will be caught by strainer  36  in the bottom of tub  5  instead of entering pump assembly  30  where they may cause damage. The combination of strainer fins  200  and rib or flow plate  198  establishes the flow and the size of entrained soil particles which can enter pump assembly  30 . Therefore, this washing fluid, which will initially be substantially clean but which will certainly pick-up additional soil during at least initial stages of a washing operation, will flow past strainer fins  200 , down into trough  129 , beneath flow plate  198 , up an opposing portion of trough  129  to an intake chamber  269  defined between lower housing plate  145  and intermediate housing plate  189 . 
     As the washing fluid is being drawn in by at least the operation of impeller  220 , the washing fluid will attempt to flow through apertured plate  182 . At this point, the rotating chopper blade  178  will function to mince any entrained particles within the washing fluid, with the particles having to be chopped sufficiently in order to enable passage through apertured plate  182 . Therefore, flowing through apertured plate  182  will be a liquid having, at most, small soil particles entrained therein. When this fluid supply is directed between pump component  218  and impeller  220 , the fluid is directed radially outwardly into a pumping chamber  270 . The fluid is then forced to reverse direction and to flow through involute manifold  226 . 
     Therefore, at involute manifold  226 , the fluid is directed radially inwardly and then upwardly, with a portion of the fluid flowing through to and causing rotation of lower wash arm  47  and a substantial portion of the fluid being directed into conduit  51 . The portion of fluid flowing into lower wash arm  47  will be sprayed into tub  5  through nozzles, such as that indicated at  271 , provided on lower wash arm  47  in order to direct the fluid upwardly against kitchenware supported upon a lower rack, as well as a portion of the fluid downwardly as will be discussed more fully below. 
     With respect to the fluid flowing through conduit  51 , a small percentage of this fluid will enter sampling port  267  so as to be directed through cylinder member  268  and into filter chamber  202 . The remaining portion of the fluid in horizontal section  53  of conduit  51  will continue to flow through vertical section  54  and upper horizontal section  55  in order to reach upper wash arm  59  which is used to provide a downward flow of washing fluid onto the kitchenware. As indicated above, a portion of the fluid flowing through conduit  51  can also be diverted through a respective port  68 ,  69  through the use of wash fluid diverter  66 . 
     The portion of the fluid that flows into filter chamber  202  will actually be forced to flow around filter chamber  202  which is open to collection chamber  212  and drain port  76 . However, when drain pump  79  is not activated, this fluid and the entrained particles therein can only initially fill up collection chamber  212  and filter chamber  202 . Once chambers  202  and  212  are filled, the fluid will be caused to flow out of pump housing  33  and back into tub  5  through the various enlarged openings  206  provided with fine mesh screen  207 . Of course, given the presence of fine mesh screen  207 , the fluid re-entering tub  5  from filter chamber  202  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  207  will be forced to remain within filter chamber  202  and will actually find their way into collection chamber  212  due to the current flow created by incoming fluid into filter chamber  202  through sampling port  267  and gravity. In any event, this cleansed washing fluid will be mixed with the remaining fluid in tub  5  and, in fact, re-mixed with the re-circulated fluid flowing out of at least lower wash arm  47  and upper wash arm  59 . 
     With this arrangement, continued recirculation of washing fluid will assure that all of the soil particles are finely chopped by blade  78  as all the washing fluid entering intake chamber  269  can only pass to pumping chamber  270  through chopper blade  178  and fixed apertured plate  182 . Furthermore, by continuing to provide a flow into sampling port  267  and further finely filtering particles entrained in this fluid by means of fine mesh screen  207 , the percentage of soil in the recirculated washing fluid actually becomes quite small. Of course, soil will be accumulating within collection chamber  212 , along with a certain percentage in filter chamber  202 . Furthermore, since the fluid is attempting to exit pump assembly  30  through fine mesh screen  207 , the underside of fine mesh screen  207  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, one of which is indicated at  273  in  FIG. 6 , in order to direct a spray of washing fluid onto fine mesh screen  207 . Therefore, this directed flow will tend to wash particles off of fine mesh screen  207  and back into filter chamber  202  and, eventually, to collection chamber  212 . 
     Regardless of this arrangement, fine mesh screen  207  can become significantly clogged so as to undesirably reduce the flow of cleansed washing fluid therethrough. Obviously, such a clogged arrangement results in an increase in pressure within filter chamber  202 . Granted, a substantial increase in pressure could cause washing fluid to flow into drain hose  85  upon exceeding a drain loop head. However, in accordance with the invention, this increased pressure forces washing fluid to flow from within filter chamber  202  into overflow tube  98 , which is in direct fluid communication with filter chamber  202  as perhaps best shown in  FIGS. 4 and 5 . Therefore, washing fluid from filter chamber  202  is forced up overflow tube  98  towards overflow housing  104 . At this time, coarse filter  106  will function to at least limit the return of soil back into tub  5  until fine mesh screen  207  is cleansed as discussed further below. 
     In accordance with the most preferred embodiment of the 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 of 6.5-8 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 25 minutes. Thereafter, a 30 minute dry cycle is entered. 
     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 10 minutes, a main rinse of 25 minutes, and 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. However, it is possible for a user to select a normal wash mode when the amount of soil on the kitchenware justifies a dirty mode. To this end, dishwasher  2  includes a turbidity sensor  275  shown mounted beneath tub  5  while projecting into washing chamber  14 , preferably in trough  129 . Of course, the use of turbidity sensors to sense soil levels in dishwashers is widely known in the art. In accordance with the present invention, if a normal wash cycle is selected but turbidity sensor  275  indicates high soil levels, the pre-programmed dirty wash cycle operational sequence will be followed. Furthermore, turbidity sensor  275  incorporates a thermistor (not separately labeled) which is used in cycling of heater element  44 . At this point, it should be noted that the location of turbidity sensor  275  within trough  129  is considered to be an advantageous feature of the invention as turbidity sensor  275  is more sensitive to turbulences developed by existing soil. Trough  129  actually functions as an air/water separator for pump assembly  30  such that the location of turbidity sensor  275  is also considered to enhance the accuracy of soil level signals. 
     In any case, during full or partial drainage operations, soil will be removed from at least collection chamber  212  when a combination of soil and washing fluid will be directed, through the operation of drain pump  79 , into drain hose  85 . During this time, it is preferred to continue the operation of pump assembly  30  in order that nozzles  273  can continue to enhance the cleaning of fine mesh screen  207 . In addition, following the last drain operation in a given dishwashing cycle, a spritzing step is performed wherein a small amount of water is introduced to fill up trough  129  in order to assure that turbidity sensor  275  is covered so that a film will not develop thereon. 
     Washing fluid will continue to be pumped into drain hose  85  while fine mesh screen  207  is being purged of food soil, at which time the washing fluid in overflow tube  98  will drop back down to a normal level. Given the inclusion of filter  106  in overflow housing  104 , only filtered washing fluid can enter tub  5  through overflow tube  98 . In the most preferred embodiment, filter  106  actually incorporates a coarse mesh screen versus the fine mesh screen  207 . Again, it should be realized that fine mesh screen  207  can become overwhelmed with food soil, particularly during pre-washes. However, coarse filter  106  performs a similar filtering function when the washing fluid with entrained soil is forced up overflow tube  98 . When a washing or rinsing operation is being performed by dishwasher  2 , it is preferred that a certain spray percentage be directed at filter  106 , such as through the angling of a number of nozzles on upper wash arm  59  or on an intermediate, rack supported wash arm (not shown). Therefore, any soil that collects in filter  106  is washed back down overflow tube  98 . When pump  30  remains activated during a drain operation, this flow of soil to drain is advantageously enhanced. During other cycles, the washing fluid sprayed on filter  106  will eventually cause collected soil to fall back to filter chamber  202  through overflow tube  98  due to gravity. There the soil would be separated from the washing fluid by fine mesh filter  207 . 
     During drain operations, certainly soil retained in collection chamber  212 , along with some of washing fluid within pump assembly  30 , will be expelled. However, not all the drainage must flow through intake and pumping chambers  267  and  270  in accordance with the invention. That is, it is desirable to have some direct fluid communication between tub  5  and drain pump  79 . In accordance with the present invention, this communication is performed through the incorporation of a flapper valve  276  which is arranged in collection chamber  212  as shown in  FIGS. 4-6  and  8 . In accordance with the most preferred embodiment, flapper valve  276  includes an upper rim portion  277  and a plurality of downwardly directed flaps or legs  278 . Although three legs  278  are shown, other configurations, such as two or four legs, could be employed with each of legs  278  constituting a wall section of collection chamber  212 , while being arranged in trough  129 . With this arrangement, when drain pump  79  is activated, the suction created in collection chamber  212  will deflect legs  278  closer together thereby permitting washing fluid from within tub  5  to directly enter collection chamber  212  and, subsequently, drain hose  85 . 
     More specifically, the inclusion of flapper valve  276  provides a preferential drain for collection chamber  212  and filter chamber  202  before the sump defined by tub  5 . That is, when a drain operation is performed, the initial flow of washing fluid and soil from filter and collection chambers  202  and  212  will prevent legs  278  from deflecting inward, i.e., the flow past legs  278  tends to keep legs  278  closed against sides of collection chamber  212 . Once this soil entrained fluid is drained, legs  278  will deflect inward to allow further draining of the washing fluid from tub  5 . Therefore, when legs  278  deflect inward, slots are created to allow flow to drain port  76 . During normal washing and rinsing operations, flapper valve  276  also advantageously prevents collected soil from returning to tub  5  about legs  278  when fine mesh screen  207  becomes clogged as an increase in pressure within filter chamber  202  will actually result in an outward biasing of legs  278 . To this end, flapper valve  276  can substantially enhance the effectiveness of potential, partial purging operations which really only require draining to occur until the point when legs  278  will deflect inward. 
       FIGS. 9-11  will now be referenced to describe the preferred construction and function of filter guard  39 . Although filter guard  39  is illustrated in each of  FIGS. 1-3 , this structure has been removed from  FIGS. 4-7  to clearly depict other structure associated with pump assembly  30 . In any event, as shown, filter guard  39  is mounted upon main housing  33  below lower wash arm  47 . Filter guard  39  includes an outer wall  279  which slopes from an inner radial portion towards an outer radial portion. As depicted, filter guard  39  actually extends substantially over strainer fins  200  but, more importantly, extends entirely over fine mesh screen  207 . In essence, without the presence of filter guard  39 , utensils and other objects could inadvertently fall within tub  5  and damage fine mesh screen  207 . Therefore, filter guard  39  is provided to shield fine mesh screen  207 , while outer wall  279  is angled to accommodate run-off of any washing fluid. 
     As clearly shown in these figures, the outer wall  279  of filter guard  39  is provided with various wash-out regions  280 , with these wash-out regions also having associated therewith mounting holes  281  in bosses  282  for securing filter guard  39  to main housing  33 . Further, along an underside of filter guard  39  at wash-out regions  280  are a plurality of ribs  283 . In addition, between adjacent bosses  282  are provided spacer ribs  285 . Indentations or recesses  289  and  290  are provided around the periphery of filter guard  39 , with recesses  289  and  290  being essentially located at mounting locations for heating element  44  as clearly illustrated in  FIG. 1 . 
     In a manner commensurate with outer wall  279 , filter guard  39  has an underside  292  which curves in order to enhance the directing of wash arm spray for the backwashing of fine mesh screen  207 . That is, as previously indicated, lower wash arm  47  includes at least one set of nozzles  273  for use in directing a spray to backwash and cleanse fine mesh screen  207 . Filter guard  39  is spaced sufficiently from pump housing cap  235  and nozzles  273  are suitably angled to accommodate this spray upon fine mesh screen  207 . However, the curvature of underside  292  further enhances this backwashing function. Wash-out regions  280  are provided for flushing out trapped food particles in connection with the overall filter guard  39 . 
     At this point, it should be noted that, although overflow tube  98  is shown to be integrated into conduit  51 , it is possible to provide a separate overflow tube  98   a  (see  FIG. 12 ). Tube  98   a  is shown to extend adjacent to conduit  51 , but actually could be directed to another portion within tub  5  distinct from conduit  51 . That is, where conduit  51  extends generally along a central portion of rear wall  11 , it is possible to direct overflow tube  98   a  to a comer or side of tub  5 . Such an arrangement could enhance the accessibility to filter  106  if changing thereof is warranted. 
     Obviously, dishwasher  2  needs to perform various operations in connection with a washing operation wherein heater  44 , drain pump  79  and pump motor  165  are controlled.  FIG. 13  schematically illustrates the control system used to regulate dishwasher  2  in the manner set forth above through a controller or CPU  295  based on operator inputs made at a control panel as generically represented at  296  and signals from turbidity sensor  275 , which also includes the thermistor as discussed above, provided in tub  5  outside of pump assembly  30 . Regardless, it should be readily apparent that the present invention provides multiple stage filtrations through the use of strainer  36 , sampling port  267  and fine mesh screen  207 . In addition, employing the filter guard advantageously protects the fine mesh filter while enhancing the backwashing thereof. To this end, it is important to note that the filter guard is fixed, as opposed to rotating with the lower wash arm, thereby reducing the weight of the rotatable wash arm assembly and simplifying the balancing. 
     In accordance with another embodiment of the present invention, as illustrated in  FIG. 14  wherein like reference numerals refer to corresponding parts, dishwasher pump  30  includes a sealing chamber  310  arranged between filter chamber  202  and collection chamber  212 . More specifically, sealing chamber  310  defines a passage (not labeled) having an opening formed in an annular flange  311  that extends between and interconnects filter chamber  202  with collection chamber  212 . Sealing chamber  310  includes an inlet portion  312  open to an exit port (not separately labeled) of filter chamber  202 , and an outlet portion  313  open to an inlet port (not separately labeled) of collection chamber  212 . Arranged within sealing chamber  310  is a sealing member, shown in the form of a check ball  316 , for selectively sealing the passage between sealing chamber  202  and collection chamber  212  during a portion of a drain operation. Preferably, check ball  316  is buoyant, such that under normal conditions, check ball  316  will float atop washing fluid residing in sealing chamber  310 . 
     At an initial phase of the drain operation, drain pump  79  is activated. The activation of drain pump  79  creates a suction force in drain port  76 . As the suction force builds, check ball  316  is drawn downward toward the inlet port of collection chamber  212 . At the same time, soil laden washing fluid in sealing chamber  310  and collection chamber  212  is expelled through drain hose  85 . Check ball  316  continues to be drawn downward until seating against annular flange  311 . At this point, the suction force seats check ball  316  against annular flange  311 , effectively stopping the flow of washing fluid from filter chamber  202 . Once the passage is sealed, the suction force causes legs  278  of flapper valve  276  to deflect inward allowing washing fluid in tub  5  to directly enter collection chamber  212  and, subsequently, drain hose  85 . 
     Once the washing fluid is drained from tub  5 , drain pump  79  begins to ingest air, causing drain pump  79  to hesitate and resulting in a decrease of the suction force. Consequently, check ball  316  is able to overcome the suction force and unseat from annular flange  311 , thereby opening the passage to filter chamber  202 . At this point, the remainder of the soil laden washing fluid from filter chamber  202  is expelled through drain port  76  and, ultimately, drain hose  85 . Since legs  278  are caused to deflect inward under the force of drain pump  79 , even if legs  278  become reversed biased during installation or there exists an insufficient pressure head in tub  5  to deflect legs  278 , the drain operation will still be effectively performed, with all the washing fluid being directed to drain hose  85 . 
     Although described with reference to a preferred embodiment of the invention, it should be readily understood that various changes and/or modifications can be made to the invention without departing from the spirit thereof. For instance, although the sealing member is disclosed as a check ball, various other forms of pressure operated valves could be employed. In any event, it should be understood that the invention is only intended to be limited by the scope of the following claims.