Patent Publication Number: US-6698438-B2

Title: Dishwasher fine filter assembly with helical flow path

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to dishwashers, and, more particularly, to dishwasher system fine filter systems. 
     Known dishwasher systems include a main pump assembly and a drain pump assembly for circulating and draining wash fluid within a wash chamber located in a cabinet housing. The main pump assembly feeds washing fluid to various spray arm assemblies for generating washing sprays or jets on dishwasher items loaded into one or more dishwasher racks disposed in the wash chamber. Fluid sprayed onto the dishwasher items is collected in a sump located in a lower portion of the wash chamber, and water entering the sump is filtered through one or more coarse filters to remove soil and sediment from the washing fluid. At least some dishwasher systems further include a fine filter system in flow communication with the main pump assembly to remove soil and sediment of a smaller size than those filtered by the coarse filters. The main pump assembly draws wash fluid from the sump to recirculate in the wash chamber, and the coarse and fine filters are used to continuously filter the water in the sump during the re-circulation process. 
     At least one known fine filter assembly includes a fine filter having a filter screen disposed over a top of a filter body. Soil and sediment is filtered from wash fluid passing through the filter screen, and soil and sediment is collected in the filter body. It is sometimes difficult to remove soil that accumulates in a filter body toward a fine filter drain. The efficiency of the filter is compromised if soil cannot be quickly and completely removed. 
     BRIEF SUMMARY OF THE INVENTION 
     In an exemplary embodiment, a fine filter assembly for a dishwasher includes a filter body having a soil accumulation trough. The soil accumulation trough defines a substantially helical flow path between a fine filter inlet and an outlet. A natural flow path is therefore provided to efficiently clean fine the filter assembly with downwardly directed fluid jets generated by a lower spray arm assembly. Soil is directed to a fine filter drain tube with relative ease, thereby facilitating use of more efficient use of a drain pump inlet as a soil collection chamber during wash cycles. 
     A fine filter screen is disposed over a top of the filter body to filter soil and sediment from fluid flowing through the fine filter assembly, and soil is accumulated in the soil accumulation trough and naturally directed toward the fine filter outlet on the sloped helical path. The soil accumulating trough includes a first end and a second end located substantially adjacent to one another so that the soil accumulation trough extends substantially 360 radial degrees around a circular outer perimeter of the filter body. Thus, a full length of the filter body is used to direct soil and sediment downwardly to the fine filter outlet. An efficient and easily cleaned filter assembly is therefore provided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view of an exemplary dishwasher system partially broken away; 
     FIG. 2 is a top plan view of a portion of the dishwasher system shown in FIG. 1 along line  2 - 2 ; 
     FIG. 3 is a partial side elevational view of the portion of the dishwasher system shown in FIG. 2; 
     FIG. 4 is a cross sectional schematic view of the portion of the dishwasher system shown in FIG. 3 along line  4 - 4 ; 
     FIG. 5 is a cross sectional schematic view of the portion of the dishwasher system shown in FIG. 2 along line  5 - 5 ; 
     FIG. 6 is a perspective view of a spray arm hub assembly for the dishwasher system shown in FIGS. 1-5; 
     FIG. 7 is a cross sectional view of the spray arm assembly shown in FIG. 6; 
     FIG. 8 is a perspective view of a fine filter assembly for the dishwasher system shown in FIGS. 1-5; 
     FIG. 9 is a perspective view of the fine filter assembly shown in FIG. 8 with parts removed; 
     FIG. 10 is a perspective view of a drain pump assembly shown in FIGS. 3-5; 
     FIG. 11 is a functional schematic of the dishwasher system shown in FIGS. 1-5 in a first mode of operation; 
     FIG. 12 is a functional schematic of the dishwasher system shown in FIGS. 1-5 in a second mode of operation; 
     FIG. 13 is a functional schematic of the dishwasher system shown in FIGS. 1-5 in a third mode of operation; 
     FIG. 14 is a functional schematic of a second embodiment of a dishwasher system shown in FIGS. 1-5 including a fine filter pressure relief; 
     FIG. 15 is a functional schematic of a third embodiment of a dishwasher system; 
     FIG. 16 is a perspective view of a second embodiment of a dishwasher fine filter assembly; 
     FIG. 17 is a cross sectional view of a third embodiment of a dishwasher fine filter assembly; 
     FIG. 18 is a functional schematic of a fourth embodiment of a dishwasher system; and 
     FIG. 19 is a functional schematic of a fifth embodiment of a dishwasher system. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is a side elevational view of an exemplary domestic dishwasher system  100  partially broken away, and in which the present invention may be practiced. It is contemplated, however, that the invention may be practiced in other types of dishwashers and dishwasher systems beyond dishwasher system  100  described and illustrated herein. Accordingly, the following description is for illustrative purposes only, and the invention is in no way limited to use in a particular type of dishwasher system, such as dishwasher system  100 . 
     Dishwasher  100  includes a cabinet  102  having a tub  104  therein and forming a wash chamber  106 . Tub  104  includes a front opening (not shown in FIG. 1) and a door  120  hinged at its bottom  122  for movement between a normally closed vertical position (shown in FIG. 1) wherein wash chamber is sealed shut for washing operation, and a horizontal open position (not shown) for loading and unloading of dishwasher contents. Upper and lower guide rails  124 ,  126  are mounted on tub side walls  128  and accommodate upper and lower roller-equipped racks  130 ,  132 , respectively. Each of upper and lower racks  130 ,  132  is fabricated from known materials into lattice structures including a plurality of elongate members  134 , and each rack  130 ,  132  is adapted for movement between an extended loading position (not shown) in which the rack is substantially positioned outside wash chamber  106 , and a retracted position (shown in FIG. 1) in which the rack is located inside wash chamber  106 . Conventionally, a silverware basket (not shown) is removably attached to lower rack  132  for placement of silverware, utensils, and the like that are too small to be accommodated by upper and lower racks  130 ,  132 . 
     A control input selector  136  is mounted at a convenient location on an outer face  138  of door  120  and is coupled to known control circuitry (not shown) and control mechanisms (not shown) for operating a fluid circulation assembly (not shown in FIG. 1) for circulating water and dishwasher fluid in dishwasher tub  104 . The fluid circulation assembly is located in a machinery compartment  140  located below a bottom sump portion  142  of tub  104 , and its construction and operation is explained in detail below. 
     A lower spray-arm-assembly  144  is rotatably mounted within a lower region  146  of wash chamber  106  and above tub sump portion  142  so as to rotate in relatively close proximity to lower rack  132 . A mid-level spray-arm assembly  148  is located in an upper region of wash chamber  106  and is located in close proximity to upper rack  130  and at a sufficient height above lower rack  132  to accommodate a largest item, such as a dish or platter (not shown), that is expected to be placed in lower rack  132  and washed in dishwasher system  100 . In a further embodiment, an upper spray arm assembly (not shown) is located above upper rack  130  at a sufficient height to accommodate a tallest item expected to be placed in upper rack  130 , such as a glass (not shown) of a selected height. 
     Lower and mid-level spray-arm assemblies  144 ,  148  and the upper spray arm assembly are fed by the fluid circulation assembly, and each spray-arm assembly includes an arrangement of discharge ports or orifices for directing washing liquid onto dishes located in upper and lower racks  130 ,  132 , respectively. The arrangement of the discharge ports in at least lower spray-arm assembly  144  provides a rotational force by virtue of washing fluid flowing through the discharge ports. The resultant rotation of lower spray-arm assembly  144  provides coverage of dishes and other dishwasher contents with a washing spray. In various alternative embodiments, mid-level spray arm  148  and/or the upper spray arm are also rotatably mounted and configured to generate a swirling spray pattern above and below upper rack  130  when the fluid circulation assembly is activated. 
     FIG. 2 is a top plan view of a dishwasher system  100  just above lower spray arm assembly  144 . Tub  104  is generally downwardly sloped beneath lower spray arm assembly  144  toward tub sump portion  142 , and tub sump portion is generally downwardly sloped toward a sump  150  in flow communication with the fluid circulation assembly (not shown in FIG.  2 ). Tub sump portion  142  includes a six-sided outer perimeter  152  having a shape reminiscent of a baseball home plate. Lower spray arm assembly is substantially centered within tub  104  and wash chamber  106 , off-centered with respect to tub sump portion  142 , and positioned above tub  104  and tub sump portion  142  to facilitate free rotation of spray arm  144 . 
     Tub  104  and tub sump portion  142  are downwardly sloped toward sump  150  so that as water sprayed from lower spray arm assembly  144 , mid-level spray arm assembly  148  (shown in FIG. 1) and the upper spray arm assembly (not shown) is collected in tub sump portion  142  and directed toward sump  150  for filtering and re-circulation, as explained below, during a dishwasher system wash cycle. In addition, a conduit  154  extends beneath lower spray arm assembly  144  and is in flow communication with the fluid circulation assembly. Conduit  154  extends to a back wall  156  of wash chamber  106 , and upward along back wall  156  for feeding wash fluid to mid-level spray arm assembly  148  and the upper spray arm assembly. 
     FIG. 3 illustrates fluid circulation assembly  170  extending below wash chamber  106  (shown in FIGS. 1 and 2) in machinery compartment  140  (shown in phantom in FIG.  3 ). Fluid circulation assembly  170  includes a main pump assembly  172  established in flow communication a building plumbing system water supply pipe (not shown) and a drain pump assembly  174  in fluid communication with sump  150  (shown in FIG. 2) and a building plumbing system drain pipe (not shown). 
     FIG. 4 is a cross sectional schematic view of dishwasher system  100 , and more specifically of fluid circulating assembly  170  through drain pump assembly  174 . Tub  104  is downwardly sloped toward tub sump portion  142 , and tub sump portion is downwardly sloped toward sump  150 . As wash fluid is pumped through lower spray arm assembly  144 , and further delivered to mid-level spray arm assembly  148  (shown in FIG. 1) and the upper spray arm assembly (not shown), washing sprays are generated in wash chamber  106 , and wash fluid collects in sump  150 . 
     Sump  150  includes a cover  180  to prevent larger objects from entering sump  150 , such as a piece of silverware or another dishwasher item that is dropped beneath lower rack  132  (shown in FIG.  1 ). A course filter  182  is located adjacent sump  150  to filter wash fluid for sediment and particles of a predetermined size before flowing into sump  150  through a course inlet filter  183 , and a turbidity sensor is coupled to sump  150  and used in accordance with known techniques to sense a level of sediment in sump  150  and to initiate a sump purge cycle when a turbidity level in sump  150  approaches a predetermined threshold. 
     A drain check valve  186  is established in flow communication with sump  150  and opens or closes flow communication between sump  150  and a drain pump inlet  188 . A drain pump  189  is in flow communication with drain pump inlet  188  and includes an electric motor for pumping fluid at inlet  188  to a pump discharge (not shown in FIG. 4) and ultimately to a building plumbing system drain (not shown). When drain pump is energized, a negative pressure is created in drain pump inlet  188  and drain check valve  186  is opened, allowing fluid in sump  150  to flow into fluid pump inlet  188  and be discharged from fluid circulation assembly  170 . 
     As explained further below, a fine filter assembly  190  is located below lower spray arm assembly and above tub sump portion  142 . As wash fluid is pumped into lower spray arm  144  to generate a washing spray in wash chamber  106 , wash fluid is also pumped into fine filter assembly  190  to filter wash fluid sediment and particles of a smaller size than coarse filters  182  and  183 . Sediment and particles incapable of passing through fine filter assembly  190  are collected in fine filter assembly  190  and placed in flow communication with a fine filter drain tube  192  received in a fine filter drain docking member  194 , which is, in turn, in flow communication with drain pump inlet  188 . Thus, when pressure in fine filter assembly  190  exceeds a predetermined threshold, thereby indicating that fine filter assembly is clogged with sediment, drain pump  189  can be activated to drain fine filter assembly. Down jets (not shown) of lower spray arm assembly  144  spray fluid onto fine filter assembly  190  to clean fine filter assembly during purging or draining of fine filter assembly  190 . 
     FIG. 5 is a cross sectional schematic view of dishwasher system  100 , and more specifically of main pump assembly  172 . A main pump  200  includes a main pump cavity  204  and an electric motor for pumping fluid from main pump cavity  204  to a main pump discharge  206 . Main pump cavity is in flow communication with a building plumbing system supply line (not shown) through a water valve (not shown) and is also in flow communication with sump  150  via a re-circulation passage  208  extending between main pump assembly  172  and drain pump assembly  174 . 
     From main pump discharge  206 , fluid is directed partly to conduit  154  for supplying wash fluid to mid-level spray arm assembly  148  (shown in FIG. 1) and to the upper spray arm assembly (not shown), partly to fine filter assembly  190  through a fine filter inlet  210  integral to conduit  154 , and partly to lower spray arm assembly  144 . Lower spray arm assembly includes a spray arm hub  212  that receives a venturi insert  214  for generating a swirling water flow through spray arm hub  212  and imparting rotary motion to a lower spray arm  216 . Fluid is sprayed through a plurality of fluid discharge ports (not shown in FIG. 5) to generate a swirling spray pattern in wash chamber  106 . 
     Wash fluid is collected in tub  104  and tub sump portion  142  and directed toward sump  150 . Fluid is filtered through coarse filter  182  and coarse inlet filter  183  and flows back to main pump cavity  204  via re-circulation passage  208 . From main pump cavity  204 , fluid is re-circulated to lower spray arm assembly  144 , conduit  154  to upper regions of dishwasher chamber  106 , and to fine filter assembly  190  for further filtering. Fluid is again collected in sump  150  and the re-circulating process continues until a purge cycle is initiated to energize drain pump  189  (shown in FIG. 4) and open drain check valve  186  (shown in FIG. 4) to pump fluid out of dishwasher system  100 . In one embodiment, fluid circulation assembly  170  is drained and flushed by operating main pump assembly  172  and drain pump assembly  174  simultaneously, as explained further below. 
     FIG. 6 is a perspective view of an exemplary lower spray arm hub assembly  230  of fluid circulation assembly  170  (shown in FIGS.  3 - 5 ). Hub assembly  230  includes spray arm hub  212  and venturi insert  214  therein. Venturi insert  214  includes a lower end  232  in flow communication with main pump discharge  206  (shown in FIG. 5) and an upper end  234  in flow communication with lower spray arm assembly  144  (shown in FIGS.  2 - 5 ). Hub  212  includes a longitudinally extending hub base  236 , a laterally extending conduit coupling member  238  extending from hub base  232 . Conduit coupling member  238  extends substantially perpendicularly to hub base  232 , includes a fine filter inlet port  240 , and includes a serrated end  242  for sealing engagement with conduit  154  (shown in FIGS. 2-5) that delivers wash fluid to mid-level spray arm assembly  144  (shown in FIG. 1) and/or the upper spray arm assembly (not shown). 
     FIG. 7 is a cross sectional view of spray arm assembly  230  and illustrating fluid paths therethrough. Hub base  236  includes a central bore  244  extending therethrough along a longitudinal axis  246 , and a conduit feed passage  248  in flow communication with central bore  244 . Venturi insert  214  extends through hub base central bore and also includes a central bore  249  extending along hub base longitudinal axis  246 . Venturi insert central bore  249  is shaped to create a negative pressure at a bearing surface (not shown in FIG. 7) of lower spray arm assembly  144  (shown in FIGS. 1-5) and therefore eliminate fluid leaks at the bearing surface. 
     Venturi insert central bore  249 , however, is smaller than hub base central bore  246  so that a fluid bypass channel  250  is created around venturi insert  214  so that wash fluid may be fed to both lower spray arm assembly  144  through venturi insert central bore  248  and to conduit feed passage  248  through bypass channel  250 . Further, conduit feed channel  248  includes fine filter inlet port  240  for feeding fluid to fine filter assembly  190  (shown in FIGS.  4  and  5 ). Consequently, when hub assembly  230  is placed in flow communication with main pump discharge  206  (shown in FIG. 5) and when conduit coupling member  238  is coupled to conduit  154 , wash fluid can be fed to lower spray arm assembly  144 , conduit  154 , and to fine filter assembly  190  through a single passage in tub  104  (shown in FIGS.  1 - 5 ), thereby eliminating potential leaks from a plurality of separate feeds through tub  104  in conventional dishwasher systems. In addition, by feeding fine filter from conduit feed passage  248  rather than directly from main pump discharge  206 , fine filter inlet pressure is lowered, which reduces a frequency of premature draining of sump  150  (shown in FIGS. 2-5) due to pressure conditions in fine filter assembly. 
     Still further, and as best depicted in FIG. 5, venturi insert  214  of hub assembly  230  extends through the single opening in tub  104  to establish flow communication with main pump discharge  206 . As such, lower spray arm  144  is of a relatively compact height in relation to known lower spray arm assemblies, and consequently less space in wash chamber  106  is occupied by lower spray arm assembly  144 . 
     FIG. 8 is a perspective view of an exemplary fine filter assembly  190  including a filter body  260  and a filter screen grid  262  coupled to body  260  for filtering particles in wash fluid of a pre-selected size determined by openings in grid  262 . Body  260  includes a fluid inlet (not shown in FIG. 8) and a drain tube  192 . 
     FIG. 9 is a perspective view of fine filter assembly  190  with filter screen grid  262  (shown in FIG. 8) removed. Body  260  is generally bowl shaped, and includes a soil accumulation trough  264  extending between fluid inlet  266  and a fluid outlet (not shown in FIG. 1) in flow communication with drain tube  192 . Soil accumulating trough includes a first end  268  adjacent fluid inlet  266  and a second end  270  adjacent the fluid outlet, and is generally sloped downwardly from first end  268  to second end  270  along a substantially helical path between first end  268  and second end  270  so that second end  270  is deeper than first end  260 . First end  268  and second  270  are situated relatively close to one another so that soil accumulating trough extends radially for nearly 360° along the helical path between first end  268  and second end  270 . In addition, soil accumulating trough  264  grows wider toward second end  270  and the fluid outlet to accommodate a relatively greater amount of sediment at second end  270  than at first end  268 . 
     It is believed that the shape and slope of soil accumulating trough  264  provides enhanced filtering performance relative to known dishwasher fine filter systems. A natural flow path is provided toward drain tube  192  that facilitates cleaning of fine filter assembly  190 . Soil is directed to drain tube  192  with relative ease, thereby facilitating use of more efficient use of drain pump inlet  188  (shown in FIG. 4) as a soil collection chamber during wash cycles. In addition, because soil accumulating trough  264  extends for nearly 360 radial degrees along its helical path in fine filter body  260 , a full length of filter body  260  is utilized for downward sloped soil accumulation between the wash fluid inlet  266  and the outlet. Consequently, the entire filter is efficiently flushed during a drain cycle. 
     A central bore  272  extends through body  260  and receives hub assembly  230  (shown in FIGS.  6  and  7 ). Fluid inlet  266  is placed in flow communication with fine filter inlet port  240  of hub conduit coupling member  238  (shown in FIGS. 6 and 7) so that wash fluid from main pump discharge  206  (shown in FIG. 5) is fed to fine filter assembly  190  via inlet port  240  and fluid inlet  266 . As explained below, flow through drain tube  192  is prevented in one embodiment by a normally closed valve (not shown in FIG. 9) when main pump assembly  174  is running. Therefore, fine filter assembly is pressurized by fluid flow from main pump assembly  174 , and wash fluid percolates through filter screen grid  262  (shown in FIG. 8) and returns to sump  150  (shown in FIGS. 2-4) for re-circulation in wash chamber  106  (shown in FIGS.  1 - 5 ). Soil and fluid sediment too large to pass through filter screen grid  262  is accumulated in soil accumulation trough  264  and directed toward second end  270  and drain tube  192 . As filter screen  162  clogs with sediment, pressure rises in fine filter assembly  190 . In one embodiment, pressure in fine filter assembly  190  is monitored and used to trigger a purge cycle of fine filter assembly  190  to drain and backwash the fine filter. 
     FIG. 10 is a perspective view of an exemplary drain pump assembly  174  including drain pump inlet  188 , drain pump  189  and a drain pump discharge  280  for coupling to a building plumbing system drain (not shown). Drain pump inlet  188  includes a fine filter drain suction inlet  282  to be placed in flow communication with fine filter drain tube  192  (shown in FIGS. 4,  8  and  9 ), a sump suction inlet  284  to be placed in flow communication with sump  150  (shown in FIGS.  2 - 5 ), and drain check valve  186  for regulating flow from sump  150  into drain pump inlet  188 . 
     FIG. 11 is a functional schematic of dishwasher system  100  as described above in a first mode of operation wherein main pump assembly  172  is running to wash dishwasher contents. Fluid flow is generally indicated by the solid arrows. As seen from FIG. 11, fluid flows from main pump  172  to lower spray arm assembly  144  through hub venturi insert  214  and through a plurality of upwardly directed fluid discharge ports  300  therein, as well as a plurality of downwardly directed fluid discharge ports  302  to create a downward spray on fine filter assembly  190 . Fluid also flows from main pump assembly  172  through hub bypass channels  250 , into conduit  154  and into fine filter assembly  190  through fine filter inlet port  240 . Fluid in conduit  154  is distributed to upper regions of wash chamber  106  and fluid in fine filter assembly  190  either flows through fine filter assembly filter screen  262  or into fine filter drain tube  192  and into drain pump inlet  188 . Fluid flows upwardly into drain line  304  until a pressure from a fluid column in drain line  304  counterbalances operating pressure in fine filter assembly  190 . Hence, as pressure in fine filter assembly increases, so does a height of the fluid column in drain tube  304 , up to a maximum height determined the height of drain line  304 . In an exemplary embodiment, drain line extends  304  upwardly about 32 inches above drain pump inlet  188  to create adequate back pressure in drain line  304  to prevent premature draining of fluid from fluid circulation dishwasher  100 . In alternative embodiments, greater or lesser drain line heights and configurations are employed to achieve similar benefits. 
     Filtered fluid is distributed into wash chamber  106 , collected in sump  150  and filtered again by coarse filters  182 ,  183  (shown in FIGS.  4  and  5 ). Check valve  186  is kept closed by pressure in filter drain tube  190  and a drain line  304 , preventing soil from fine filter assembly  190  from entering sump  150  and further preventing fluid in sump  150  from entering drain pump inlet  188 . Fluid in sump  150  is therefore re-circulated as described above by main pump assembly  172 . 
     FIG. 12 is a functional schematic of dishwasher system  100  in a second mode of operation wherein a drain cycle is initiated and main pump assembly  172  and drain pump  189  are simultaneously operated for a predetermined time period to drain sump  150  and flush fine filter assembly  190 . As noted previously, pressure in fine filter is lowered due to indirect fluid feed from main pump assembly  172  through conduit feed passage  248  and fine filter inlet passage  240 . Because of the lower pressure in fine filter assembly  190 , it is possible to activate drain pump  189  and still open drain check valve  186 , despite the fact that main pump assembly  172  is running. Therefore, when drain pump  189  is energized and check valve  186  is opened, water in sump  150  is partly drained and partly re-circulated. Also, when drain check valve  186  is opened, fine filter assembly  190  receives both an inlet flow from conduit feed passage  248  and fine filter water inlet  240 , and a backflush from lower spray arm downwardly directed fluid discharge ports  302 . Backflushing of fine filter assembly aids in clearing filter screen grid  262  (shown in FIG. 8) and appreciably improves soil removal from fine filter assembly during a drain cycle. At a predetermined time, dependant upon main pump assembly and drain pump assembly characteristics, main pump assembly  172  is de-energized to avoid surging noises due to low water levels in sump  150 . 
     FIG. 13 is a functional schematic of dishwasher system in a third mode of operation wherein a drain cycle continues after main pump assembly  172  is de-energized. Drain pump  189  pumps remaining fluid in fine filter assembly  190 , lower spray arm assembly  144 , conduit  154 , sump  150  and main pump assembly  172  through check valve  186  and into drain line  304 . When fluid has been removed from dishwasher system  100 , drain pump  189  is de-energized, and drain check valve  186  is again closed. In a further embodiment, another check valve (not shown) or another coarse filter (not shown) is used to prevent soiled water from drain line  304  from flowing backward into fine filter assembly  190 . 
     FIG. 14 is a functional schematic of second embodiment of a dishwasher system  308  wherein common components of dishwasher system  100  are indicated with like reference characters. Dishwasher system  308  includes a pressure actuated fine filter check valve  310  for regulating flow through fine filter drain tube  192 . Fine filter check valve  310  is normally closed so that fine filter assembly  190  is pressurized. Wash fluid pumped into fine filter assembly  190  may only exit fine filter assembly through fine filter screen grid  262  (shown in FIG.  8 ). While indirect feeding of fine filter assembly  190  through conduit feed passage  248  and fine filter inlet passage  240 , rather than directly from main pump assembly  172  provides a reduced pressure in fine filter assembly  190 , as filter screen grid  262  clogs with sediment, pressure in fine filter assembly  190  rises. 
     Unlike known fine filter assemblies including a pressure relief port integral to fine filter assembly itself, a pressure relief tube  312  is provided in flow communication with fine filter assembly  190  to prevent pressure in fine filter assembly  190  from exceeding a predetermined level. In one embodiment, pressure relief tube extends adjacent conduit  154  that feeds mid-level spray arm assembly  148  (shown in FIG. 1) and the upper spray arm assembly (not shown) and includes a vertical portion  314  that extends upwardly for a height H that is less than a height of upwardly extending drain line  304 . Vertical portion  314  includes an open top  316  and hence forms a standpipe to regulate fluid pressure in fine filter assembly  190 . As pressure rises in fine filter assembly  190 , fluid flows into pressure relief tube  312  and begins to rise in vertical portion  314 . Pressure in fine filter assembly  190  is therefore balanced by the fluid column in relief tube vertical portion  314 . When pressure in fine filter assembly  190  is sufficient to force fluid the full height H in vertical portion  314 , fluid overflows vertical portion  314  and through open top  316 . 
     Pressure may therefore rise in fine filter assembly  190  up to a maximum pressure, determined by height H of the fluid column in vertical portion, and the maximum pressure is then maintained in fine filter assembly  190 . Pressure relief tube open top  316  is distanced from downwardly directed fluid discharge ports  302  of lower spray arm assembly  144 , thereby avoiding possible pressure effects of operation of lower spray arm assembly  144  that could compromise pressure relief in fine filter assembly  190 . Also, the location of pressure relief tube  312  alongside conduit  154  and near a vertical wall of tub  104  renders pressure relief tube open top  316  less vulnerable to soiled fluid re-entering the wash system. Still further, because height H of pressure relief tube is less than a height of drain line  304 , fluid flows through open top  316  of pressure relief tube  314  rather than continuing to rise in drain line  304  and eventually flowing into a sewer system (not shown). 
     A relatively simple and reliable pressure relief system is therefore provided that is believed to be more effective than known fine filter pressure relief systems including pressure relief openings in a top of the fine filter. 
     In further embodiments, enhanced fine filter pressure regulation is achieved with optimization of main pump assembly  172 , optimization of lower spray arm assembly, optimization of downwardly directed fluid discharge ports  302 , optimization of fine filter assembly  190  geometry and flow paths, flow sensors, and/or drain line  304  water level sensors (not shown). By monitoring conditions in fine filter assembly  190  and/or drain line  304 , drain pump assembly  174  may be activated to open check valves  186  and  310  to drain fine filter assembly  190  and sump  150 . 
     Fine filter drain tube check valve  310  facilitates pressure regulation in fine filter assembly and prevents fluid in drain line  304  from flowing back into fine filter assembly  190  when main pump assembly  172  is de-energized. It is appreciated, however, that the benefits of the above-described fine filter pressure relief system, may be achieved in the absence of filter drain check valve  310 . 
     FIG. 15 is a functional schematic of a third embodiment of a dishwasher system  330  wherein common elements of dishwasher system  100  are indicated with like reference characters. Dishwasher system  330  includes, in addition to drain pump  189 , a separate fine filter drain pump  332  in flow communication with fine filter assembly drain tube  192  through a check valve  334  and also in flow communication with drain line  304 . Drain pump  189  is therefore used solely to drain sump  150  and fine filter drain  332  is used solely to drain fine filter assembly  190 . Drain pumps  189 ,  332  are both fed to drain line  304 . 
     In one embodiment, drain pump  189  is de-energized when a drain cycle is initiated, and fine filter drain  332  is energized to drain sump  150  through fine filter assembly  190 , thereby elongating a flush time of fine filter assembly  190  when main pump assembly  172  is energized. Drain pump  189  is then briefly energized to drain accumulated soil from sump  150 . In further embodiments, drain pumps  189 ,  332  are cycled on and off in varying sequences, either sequentially or simultaneously to drain sump  150  and fine filter assembly  190  to meet performance objectives. 
     In addition, fine filter drain pump  332  facilitates independent draining of fine filter assembly  190  while main pump assembly  172  is running, such as, for example, with feedback controls in response to pressure conditions in fine filter assembly  190 . Thus, for example, fine filter assembly  190  may be drained multiple times, if needed, while main pump assembly  172  continues its wash cycle. Wash cycles may therefore continue without interruption to drain fine filter assembly  190 , and fine filter assembly  190  performance may be improved with more frequent draining and backflushing of filter screen grid  262  (shown in FIG. 8) through activation of fine filter drain pump  332 . 
     FIG. 16 is a perspective view of a second embodiment of a dishwasher fine filter assembly  350  including a filter body  352  and an integral conduit  354  for feeding wash fluid to upper regions of dishwasher chamber  106  (shown in FIG.  1 ). Body  352  includes a soil accumulating trough  356  extending around an outer perimeter  358  of body  352 . Soil accumulating trough  356  includes a shallow end  360  in flow communication with a fine filter inlet (not shown in FIG. 16) integral to conduit  354 , and a deep end  362  in flow communication with a fine filter drain tube  364 . Soil accumulating trough  356  is sloped from shallow end  360  to deep end  262  and extends substantially 360 radial degrees around body outer perimeter  358 , thereby producing a substantially helical flow path in soil accumulating trough  356 . Because soil accumulating trough  264  extends for nearly 360 radial degrees along its helical path in fine filter body  260 , a full length of filter body  352  is utilized for downward sloped soil accumulation between the fluid inlet and outlet. Consequently, the entire filter is efficiently flushed during a drain cycle. A fine filter screen material (not shown in FIG. 16) is placed over soil accumulation trough to filter fluid particles or a pre-selected size from wash fluid passing through fine filer assembly  350  in a substantially similar fashion to that described above with respect to filter assembly  190  (shown in FIGS. 3,  4 ,  8 ,  9  and  11 - 15 ). 
     FIG. 17 is a cross sectional view of a third embodiment of a dishwasher fine filter assembly  370  wherein common elements of fine filter assembly  350  (shown in FIG. 16) are indicated with like reference characters. Soil accumulating trough  356  extends along an outer perimeter  358  of filter body  352 . A fine filter screen  372  is disposed over filter body  352  and soil accumulating trough  356 , and a weir  374  extends upward from filter body  352  along body outer perimeter  358 . Weir  374  forms a barrier around body outer perimeter  358  so that fluid may pool within weir  374  to submerge fine filter screen  372  in use. The pooled fluid is suctioned through filter screen  372  when filter assembly  370  is drained, thereby facilitating cleaning and flushing of filter screen  372 . When weir is properly dimensioned, fine filter assembly  370  may be flushed with a minimal amount of water, and unlike some known fine filter systems, may be located above a fluid line in tub sump portion  142  (shown in FIGS.  2 - 5 ). Fine filter assembly  370  therefore facilitates improved filter screen backflushing and minimizes an amount of fluid needed to prime main pump assembly  172  in use. 
     FIG. 18 is a functional schematic of a fourth embodiment of a dishwasher system  400  wherein common elements of dishwasher system  100  (shown in FIGS. 1-13) are indicated with like reference characters. Main pump assembly  172  feeds lower spray arm assembly  144 , a fine filter body  402  through spray arm bypass passages  404 , and a spray arm conduit  406 . Fluid in fine filter body  402  is therefore pressurized and passed through a fine filter screen  410 , and particles in wash fluid too large to pass through filter screen  410  are accumulated a in helical soil accumulating trough  411  and directed toward a fine filter outlet  412 . Lower spray arm assembly  144  includes downwardly directed fluid discharge ports  302  for discharging soil particles from filter screen  410  and to sweep soil particles toward fine filter outlet  412 . 
     A fine filter drain tube  414  extends from fine filter outlet  412  and is fitted with a pressure actuated, normally closed double diaphragm valve  416 . Valve  416  includes a primary diaphragm  418  and a secondary diaphragm  419 . Primary diaphragm  418  is closed in normal operation when main pump assembly  172  is running to execute a wash cycle. 
     Because fine filter drain tube  414  is fitted with a normally closed valve  418 , water entering fine filter body  402  is pressurized and may only exit through fine filter screen  410 , thereby retaining all particles larger than the screen opening size. Filtration continues until the wash cycle ends and main pump assembly  172  is de-energized, thereby returning pressure in fine filter body to substantially atmospheric pressure, i.e., fine filter body  402  is depressurized. When drain pump  189  is energized, valve  418  is opened and fine filter body  402  is drained through drain tube  414 , together with sump  150 . Once fine filter valve  414  is opened, main pump assembly is re-energized for a predetermined time period, such as, for example, 30 seconds to backflush fine filter screen  410  and body  402 . In an alternative embodiment, main pump assembly  172  is energized substantially the entire time that sump  150  is drained for an elongated fine filter flush time. 
     In the above-described embodiment, sump  150  and fine filter body  402  may only be drained simultaneously, and only after fine filter body  150  has been depressurized, i.e., only after main pump assembly  172  is de-energized. 
     FIG. 19 is a functional schematic of a fifth embodiment of a dishwasher system  420  wherein common components of dishwasher system  400  (shown in FIG. 18) are indicated with like reference characters. Dishwasher system  420  is substantially similar to dishwasher  400  but includes a pressure actuated flapper valve  422  fitted to fine filter drain tube  414 . Flapper valve  422  allows double diaphragm valve  418  to be actuated open even while main pump assembly  172  is running by applying the full suction of drain pump  189  to fine filter drain tube  414  when flapper valve  422  is closed, thereby blocking flow communication between drain pump inlet  189  and sump  150 . Fine filter body  402  can therefore be drained at any time, even when main pump assembly  172  is running. A water valve (not shown) is opened to replace the volume of water drained when draining and flushing fine filter body  402 . Thus, one or more mini-fills of, for example, 0.1 or 0.2 gallons of fresh water may be employed to replace highly concentrated soiled water in fine filter assembly with an equal volume of fresh water in a variety of wash cycles to optimize water temperature, energy consumption, cycle speed, and other performance parameters. 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.