Abstract:
A self-cleaning filter for a washing apparatus. Water entering a filter assembly travels along a spiral pathway that facilitates the separation of heavy solid debris from the water. A filter element prevents both light and heavy solid debris from entering a conduit leading to spray nozzles, thereby preventing clogging of the nozzles. In a filter cleaning operation, solid debris is removed from the filter assembly.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to fluid filtration, and more particularly to a self-cleaning filter for water filtration. 
     BACKGROUND OF THE INVENTION 
     Washers are frequently used to clean articles used in the care of laboratory animals, such as animal cages (e.g., wire cages and plastic boxes), racks, debris pans, watering devices, bottles, and feeder bowls. These articles are often heavily soiled with solid debris (including, but not limited to, residues and dirt) from bedding, foodstuffs and animal wastes. One type of washer widely used for cleaning such articles are tunnel washers. Tunnel washers are typically divided into a plurality of processing chambers, wherein pre-washing, washing, rinsing and drying operations are respectively performed. During the pre-washing, washing and rinsing operations various fluids, including, but not limited to, water and water vapor, are introduced and removed from the respective chambers. During drying operations, heated air is circulated through a drying chamber to dry the article. 
     The process for removing dirt and debris begins in the pre-washing chamber, where spray jets or nozzles are used to spray hot water onto the article. Water sprayed into the pre-washing chamber is collected in a sump, and removed from the tunnel washer through a drain. 
     In order to conserve water and improve efficiency, it is advantageous to re-use at least some of the water collected in the sump by recirculating the used water back into the pre-washing chamber through the washer nozzles. Since the articles are typically heavily soiled when passing through the pre-washing chamber, the water collected in the sump may contain solid debris large enough to clog the washer nozzles. Therefore, before the water collected by the sump can be re-used the water must pass through a filter to remove solid debris that could cause the washer nozzles to become clogged. In order to maintain effective operation of this filter, periodic filter cleaning is necessary. 
     Existing filters have numerous drawbacks. In this regard, existing filters require frequent cleaning operations (e.g., backflushing) in order to maintain effective operation of the filter. Other problems with existing filters are the cost and complexity of devices (e.g., motors and/or blades) needed to carry out filter cleaning operations. The present invention addresses these and other drawbacks of existing filters. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, there is provided a filter assembly comprising: (a) a filter element including: a perforated wall member defining a chamber having an open end and a closed end; and (b) a plunger moveable between a first position and a second position, said plunger including: a scraper element operable to remove solid debris from said chamber, said scraper element fixed at a first end of the plunger extending into said chamber, and a stopper element fixed at a second end of the plunger distal from the first end of the plunger. 
     In accordance with another aspect of the present invention, there is provided a filter assembly comprising: a filter element including a filter wall having a plurality of perforations formed therein, said filter wall defining an inner region having an open end and a closed end; an outer wall surrounding the filter wall, said outer wall and said filter wall defining a cavity surrounding said inner region; a housing surrounding the outer wall, said housing and said outer wall defining an outer chamber; and a plunger movable between a first position and a second position to remove solid debris from said inner region and said plurality of perforations. 
     In accordance with still another aspect of the present invention, there is provided a filter assembly comprising: a cylindrical conduit wall; a filter element generally coaxial with the conduit wall, and including a cylindrical filter wall having a plurality of perforations formed therein, said cylindrical filter wall defining a filter chamber having an open end in fluid communication with a return conduit and a closed end; and a housing surrounding said filter wall, wherein said housing and said filter wall define a first annular region of the filter assembly. 
     An advantage of the present invention is the provision of a filter assembly having a self-cleaning filter element. 
     Another advantage of the present invention is the provision of a filter assembly having a filter element that prevents clogging of spray nozzles. 
     Still another advantage of the present invention is the provision of a filter assembly that can effectively and efficiently filter water containing a significant quantity of solid debris. 
     Still another advantage of the present invention is the provision of a filter assembly that minimizes maintenance requirements for a filter element. 
     Yet another advantage of the present invention is the provision of a filter assembly that is less expensive to manufacture than existing filter assemblies. 
     These and other advantages will become apparent from the following description of a preferred embodiment taken together with the accompanying drawings and the appended claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may take physical form in certain parts and arrangement of parts, a preferred embodiment of which will be described in detail in the specification and illustrated in the accompanying drawings which form a part hereof, and wherein: 
         FIG. 1  is a schematic, side elevational view of a pre-washing section of a tunnel washer, including a filter assembly according to a first embodiment of the present invention; 
         FIG. 2  is a cross-sectional view of the filter assembly of  FIG. 1 , during a filtration operation; 
         FIG. 3  is a cross-sectional view of the filter assembly taken, along lines  3 - 3  of  FIG. 2 ; 
         FIG. 4  is a cross-sectional view of the filter assembly, taken along lines  4 - 4  of  FIG. 2 ; 
         FIG. 5  is a cross-sectional view of the filter assembly shown in  FIG. 2  during a filter cleaning operation; 
         FIG. 6  is a cross-sectional view of a filter assembly according to a second embodiment of the present invention; 
         FIG. 7  is a cross-sectional view of the filter assembly, taken along lines  7 - 7  of  FIG. 6 ; 
         FIG. 8  is an enlarged cross-section view of a portion of the filter assembly shown in  FIG. 6 , wherein a filter element is joined to a return conduit; 
         FIG. 9  is a cross-sectional view of the filter assembly, taken along lines  9 - 9  of  FIG. 6 ; and 
         FIG. 10  is a cross-sectional view of a filter assembly according to the second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings wherein the showings are for the purposes of illustrating a preferred embodiment of the invention only and not for the purposes of limiting same,  FIG. 1  shows a schematic, side elevational view of a pre-washing section of a tunnel washer  10 . A housing  20  defines an inner chamber that is divided into a plurality of processing chambers, namely, a pre-washing chamber  12 , a washing chamber (not shown), a rinsing chamber (not shown) and a drying chamber (not shown). For the purpose of illustrating the present invention, only pre-washing chamber  12  will be shown and described. 
     A conveyer  30  is located within housing  20  to convey articles  4  through tunnel washer  10 . Conveyer  30  is a conventional conveyer device generally comprised of a conveyer belt  32  and rollers  34  that are driven by a motor  36 . Conveyer belt  32  extends through the plurality of processing chambers. 
     In the illustrated embodiment, articles  4  to be processed by tunnel washer  10  are loaded onto conveyer belt  32  at loading end  22  of tunnel washer  10 . An opening  24  formed in housing  20  is dimensioned to allow articles  4  to enter pre-washing chamber  12 . After processing by tunnel washer  10  is completed, articles  4  are removed from conveyer belt  32  at an unloading end of tunnel washer  10  (not shown). 
     With reference to pre-washing chamber  12 , a sump  40 , located below conveyer belt  32 , collects liquid from chamber  12 . A heating element  26  heats the water collected in sump  40 . A recirculation conduit  50  is in fluid communication with sump  40  and a return conduit  60  to recycle liquid collected by sump  40  back into pre-washing chamber  12 . Return conduit  60  includes a lower outlet portion  62   a  and an upper outlet portion  62   b . Lower outlet portion  62   a  is located in a lower region of chamber  12 , while upper outlet portion  62   b  is located in an upper region of chamber  12 . Lower outlet portion  62   a  and upper outlet portion  62   b  include a plurality of spray jets or nozzles  64  to spray liquid into chamber  12 . 
     A pump  44 , powered by motor  46 , is provided in recirculation conduit  50  to pump liquid from sump  40  through recirculation conduit  50 . 
     An exit conduit  52  fluidly connects recirculation conduit  50  with a drain conduit  54 . Drain conduit  54  is in fluid communication with a drain. A first drain valve  56  is disposed in exit conduit  52 . First drain valve  56  is movable between an open position and a closed position, to control the flow of fluid through exit conduit  52  into drain conduit  54 . 
     A filter assembly  70 , according to the present invention, is disposed between recirculation conduit  50  and return conduit  60 . Filter assembly  70  is in fluid communication with recirculation conduit  50 , return conduit  60  and drain conduit  54 , Filter assembly  70  provides filtration of the water before it is returned to pre-washing chamber  12 , as will be described in detail below. A second drain valve  58  is disposed between filter assembly  70  and drain conduit  54 . Second drain valve  58  is moveable between an open position and a closed position to control fluid flow from filter assembly  70  into drain conduit  54 . 
     A clean water conduit  18  is in fluid communication with pre-washing chamber  12  to supply clean water to chamber  12  from a source of clean water. A water inlet valve  16  is disposed within clean water conduit  18  to control the flow of clean water into pre-washing chamber  12 . 
     A controller  14  provides control signals for operation of conveyer motor  36 , pump motor  46 , first drain valve  56 , second drain valve  58 , and inlet valve  16 . Controller  14  preferably takes the form of a programmable microcontroller or microcomputer. 
     In accordance with the illustrated embodiment shown in  FIG. 2 , filter assembly  70  is generally comprised a tubular housing  90 , a lower section  80  of return conduit  60 , a filter element  120 , and a piston or plunger  150 . 
     Housing  90  is comprised of a plurality of tubular housing sections  90   a ,  90   b  and  90   c . Housing section  90   a  includes a side entry port  99  located at the upper end thereof, as best seen in  FIG. 3 . Side entry port  99  is in fluid communication with recirculation conduit  50 . Housing section  90   b  includes a funnel portion  94  to direct the flow of solid debris and water toward the center of housing  90 . Housing section  90   c  includes an enlarged portion  96  and a funnel portion  98 . Annular flanges  92  are formed at the upper and lower ends of housing section  90   a  and housing section  90   b . Annular flanges  92  are also formed at upper end of housing section  90   c . In addition, an annular flange  82  surrounds the outer surface of lower section  80  of return conduit  60 . 
     Conventional split ring clamps  110  are used to sequentially join lower section  80  of return conduit  60 , and housing sections  90   a ,  90   b  and  90   c . As best seen in  FIG. 3 , split ring clamps  110  are comprised of first and second semi-circular sections  110   a ,  110   b . First and second semi-circular sections  110   a ,  110   b  are pivotally connected to each other by pivot means  112  at a first end of sections  110   a ,  110   b . First and second semi-circular sections  110   a ,  110   b  are connected to each other by fastening means  114  at a second end of sections  110   a ,  110   b.    
     A first split ring clamp  110  joins annular flange  82  of lower section  80  to annular flange  92  at upper end of housing section  90   a . A second split ring clamp  110  joins annular flange  92  at lower end of housing section  90   a  to annular flange  92  at upper end of housing section  90   b . A third split ring clamp  110  joins annular flange  92  at lower end of housing section  90   b  to annular flange  92  at upper end of housing section  90   c.    
     Housing  90  defines a plurality of regions of filter assembly  70 , including an upper region  102 , a lower region  104  and a bypass region  106 . Housing  90  and lower section  80  of return conduit  60  are spaced to define an outer annular region or chamber  100 . 
     In the illustrated embodiment, filter element  120  is formed as a portion of lower section  80  of return conduit  60 . Filter element  120  is basically comprised of a cylindrical inner wall  124  formed inside cylindrical wall  84  of lower section  80 . Cylindrical inner wall  124  and wall  84  are spaced to define an annular region or cavity  140  inside lower section  80  of return conduit  60 . Cylindrical inner wall  124  also defines an inner region or chamber  132  inside lower section  80  of return conduit  60 . Inner chamber  132  has a closed end  126  and an open end  128 . Open end  128  of inner chamber  132  is in fluid communication with upper region  102  of filter assembly  70 . Perforations are formed in inner wall  124  to allow fluid to pass between inner chamber  132  and annular cavity  140 . 
     Plunger  150  is basically comprised of a rod  152 , a scraper element  160  and a stopper element  170 . Threaded sections  154  extend from upper and lower ends of rod  152 . 
     In the illustrated embodiment, scraper element  160  is disk shaped having an annular outer edge surface  162 . The diameter of scraper element  160  is substantially the same as the inner diameter of inner chamber  132 , but allowing a small clearance therebetween to allow scraper element  160  to be moveable within inner chamber  132 , as will be described below. Scraper element  160  also includes a hole formed generally in the center thereof to mount scraper element  160  onto threaded section  154  at the upper end of rod  152 . A nut  156  secures scraper element  160  to the upper end of rod  152 . 
     According to the illustrated embodiment, stopper element  170  generally takes the form of a disk having a plurality of recesses or notches  174  formed therein, as best seen in  FIG. 4 . The diameter of stopper element  170  is substantially the same as the inner diameter of housing section  90   c  defining lower region  104 , but allowing a small clearance therebetween to allow stopper element  170  to be moveable within lower region  104 , as will be described below. Stopper element  170  also includes a hole formed generally in the center thereof to mount stopper element  170  onto threaded section  154  at the lower end of rod  152 . A nut  156  secures stopper element  170  to the lower end of rod  152 . 
     Plunger  150  is moveable between an upper position ( FIG. 2 ) and a lower position ( FIG. 5 ). As plunger  150  moves between the upper and lower positions, scraper element  160  moves through inner chamber  132  to remove any solid debris blocking or lodged within perforations  130 , as will be described in detail below. 
     When plunger  150  is in the upper position ( FIG. 2 ), scraper element  160  is located at the upper end of inner chamber  132 , and stopper element  170  is located at the upper end of lower region  104 . When stopper element  170  is located in lower region  104 , stopper element  170  traps most solid debris, thus preventing solid debris from moving downward past stopper element  170 . At the same time, stopper element  170  allows water to flow downward past stopper element  170 . In this regard, water flows through the openings formed by notches  174  of stopper element  170 . As indicated above, funnel portion  94  of housing section  90   c  directs the flow of water and solid debris toward the center of housing  90 . 
     When plunger  150  is in the lower position ( FIG. 5 ), scraper element  160  is located at the lower end of inner chamber  132 , and stopper element  170  is located in bypass region  106 . Both water and solid debris can flow past stopper element  170  when stopper element  170  is located in bypass region  106 . In this regard, the diameter of enlarged portion  96  of housing section  90   c  is larger than the diameter of stopper element  170 , thereby providing an annular gap  97  dimensioned to allow both water and solid debris to travel downward past stopper element  170 . Funnel portion  98  of housing section  90   c  directs the flow of both water and solid debris toward the center of housing  90 . 
     For the purpose of describing an embodiment of the present invention, sump  40 , pump  44 , recirculation conduit  50 , filter assembly  70  and return conduit  60  are collectively referred to herein as a “circulation system” for circulating fluid (i.e., water) through pre-washing chamber  12 . 
     Operation of filter assembly  70  will now be described in detail with particular reference to  FIGS. 2-5 . As indicated above, articles  4  are ordinarily heavily soiled when passing through pre-washing chamber  12 . Accordingly, the dirty water collected in sump  40  will usually contain a significant amount of solid debris. Therefore, before the water can be recycled back into prewashing chamber  12 , the water collected by sump  40  must first be subject to filtration to remove solid debris that could clog nozzles  64 , as will be described in detail below. 
     Before water is initially circulated through filter assembly  70 , plunger  150  will be located at the lower position shown in  FIG. 5 , due to gravity. To “prime” the circulation system with a volume of water sufficient to effectively pre-wash articles  4 , controller  14  transmits a control signal to move inlet valve  16  from a closed position to an open position. Consequently, clean water from the clean water source enters pre-washing chamber  12  through clean water conduit  18 . The clean water entering pre-washing chamber  12  collects in sump  40 . Controller  14  also transmits control signals to move both drain valves  56  and  58  to the closed position and activates motor  46  of pump  44 . As a result, water collected in sump  40  is pumped through recirculation conduit  50  to filter element  120 . Since valve  58  is in a closed position, water will initially fill bypass chamber  106  below stopper element  170 . As the space below stopper element  170  fills with water, pressure will increase below stopper element  170 , and cause plunger  150  to rise upward to the upper position ( FIG. 2 ). As water continues to accumulate in filter assembly  70 , lower region  104  and upper region  102  fill with water. The water level inside filter assembly  70  continues rising as additional water fills sump  40  and is pumped into filter assembly  70 . Eventually, the water inside filter assembly  70  reaches a level wherein water fills inner chamber  132  and passes through perforations  130  to annular cavity  140 . Water entering annular cavity  140  travels through return conduit  60  to lower and upper outlet portions  62   a ,  62   b  ( FIG. 1 ). Water pressure inside return conduit  60  forces water out through nozzles  64 , thereby spraying water into pre-washing chamber  12 . The water sprayed into pre-washing chamber  12  is collected in sump  40  and again recirculated back into pre-washing chamber  12  by circulating through recirculation conduit  50 , filter assembly  70 , and return conduit  60 . 
     After the circulation system has been primed with a sufficient volume of water from the clean water source, controller  14  transmits a control signal to move inlet valve  16  from the open position to the closed position. It should be appreciated that a float level (not shown) may be used to ascertain whether the volume of water in the circulation system has reached a sufficient volume for effective pre-washing. 
     After the circulation system has been primed with water, tunnel washer  10  can be operated to pre-wash articles  4  traveling through pre-washing chamber  12 . To commence a pre-washing operation, motor  36  is activated by controller  14 , thereby causing rollers  34  to drive conveyer belt  32 . As a result, articles  4  loaded onto conveyer belt  32  will travel through pre-washing chamber  12  as water is sprayed from nozzles  64 . Dirty water is collected in sump  40  and is pumped by pump  44  through recirculation conduit  50  into filter assembly  70 . Filter assembly  70  functions to remove solid debris from the dirty water before recycling the water back into pre-washing chamber  12  through return conduit  60 . Therefore, filter assembly  70  prevents solid debris from clogging nozzles  64 . 
     Water from recirculation conduit  50  enters annular region  100  through side entry port  99  formed in the side of housing section  90   a , as best seen in  FIG. 3 . The side entry into the upper end of annular region  100  causes the water to initiate a rotational flow, whereby the water spirals around outer wall  84  of lower section  80  in a downward direction (see  FIG. 2 ). As the water continues the downward spiral the water moves into upper region  102 . Heavier solid debris, falls to the lower end of upper region  102 . Stopper element  170  prevents the solid debris from falling into lower region  104 , as shown in  FIG. 2 . 
     Lower pressure in return conduit  60  cause the water to flow into inner chamber  132 . The water carries lighter solid debris into inner chamber  132 . As the water continues to flow in the direction of lower pressure in return conduit  60 , the water passes through perforations  130  of filter element  120  as it travels into annular cavity  140 . Perforations  130  are dimensioned to block the passage of solid debris that is large enough to clog nozzles  64 . Water entering annular cavity  140  continues traveling through return conduit  60  to lower and upper outlet portions  62   a ,  62   b . Accordingly, the recycled water is released into pre-washing chamber  12  through nozzles  64 . 
     Most of the lighter solid debris that is blocked by filter element  120  will eventually settle downward into lower end of upper region  102 . Stopper element  170  traps most of the lighter solid debris, thus preventing the lighter solid debris from moving downward past stopper element  170 . 
     Some solid debris may block or become lodged in perforations  130  of filter element  120 , or become trapped (e.g., float) within inner chamber  132 . The flow of water through perforations  130  will decrease as more solid debris blocks or becomes lodged in perforations  130  and/or becomes trapped within inner chamber  132 . Consequently, it becomes necessary to periodically perform a filter cleaning operation to remove solid debris from perforations  130  and inner chamber  132 , and thus maintain filter efficiency and adequate water flow through filter element  120 . 
     A filter cleaning operation may be initiated in response to a water pressure or a water flow rate that is below a predetermined level. In this regard, a pressure sensor (not shown) or a flow sensor (not shown) may provide data signals to controller  14  indicative of pressure or flow rate at a location along the circulation system (e.g., at return conduit  60  or pump  44 ). If controller  14  determines that the pressure or flow rate is below a predetermined level, a filter cleaning operation may be initiated. Alternatively, a filter cleaning operation may be initiated by controller  14  after a predetermined period of time has elapsed, or in response to a signal manually generated by an operator. 
     When a filter cleaning operation is initiated, conveyer motor  36  may be deactivated by controller  14 , thereby causing conveyer belt  32  to stop moving. Furthermore, controller  14  transmits control signals to move valve  58  from a closed position to an open position. Water located below stopper element  170  in lower region  104  and bypass region  106  will immediately flow into the drain through drain conduit  54 . Controller  14  may also transmits a control signal to move valve  56  from a closed position to an open position. Accordingly, exit conduit  52  is used to provide an additional pathway for water in recirculation conduit  50  to flow into drain conduit  54 . 
     If pump  44  remains activated during the filter cleaning operation, then the water pressure inside filter assembly  70  will cause plunger  150  to move from the upper position ( FIG. 2 ) to the lower position ( FIG. 5 ). If controller  14  transmits a control signal to deactivate pump  44  during the filter cleaning operation, then the weight of the water inside filter assembly  70  will cause plunger  150  to move from the upper position ( FIG. 2 ) to the lower position ( FIG. 5 ). 
     As scraper element  160  moves downward through inner chamber  132 , scraper element  160  will remove from inner chamber  132  solid debris blocking or lodged in perforations  130 , as well as any solid debris that has become trapped in inner chamber  132 . 
     Stopper element  170  moves downward, and eventually comes to rest in bypass region  106  ( FIG. 5 ). As indicated above, when stopper element  170  is located in bypass region  106  both water and solid debris can flow around stopper element  170  through annular gap  97 . Therefore, solid debris will flow into the drain through drain conduit  54 . Valve  58  remains in the open position to allow some or all of the water in the circulation system to flow into the drain. 
     After the filter cleaning operation is completed, controller  14  transmits a control signal to move valves  56  and  58  to the closed position. Inlet valve  16  is moved from the closed position to the open position by controller  14 , in order to replace some or all of the drained water with clean water from the clean water source. If motor  46  has been deactivated, controller  14  also transmits a control signal to activate motor  46  of pump  44 . As a result, water collected in sump  40  is pumped through recirculation conduit  50 , and fills filter assembly  70  in a manner similar to the water priming operation described above. As filter assembly  70  fills with water, increased water pressure causes plunger  150  to rise upward to the upper position ( FIG. 2 ). As water fills inner chamber  132 , the water will pass through perforations  130  to annular cavity  140 . Water entering annular cavity  140  travels through return conduit  60  to lower and upper outlet portions  62   a ,  62   b  ( FIG. 1 ). Water pressure inside return conduit  60  forces water out through nozzles  64 , thereby spraying water into pre-washing chamber  12 . This water is again collected in sump  40  and recirculated through the circulation system. 
     Once the water circulating in the circulation system has been replenished to a volume sufficient for a pre-washing operation, controller  14  transmits a control signal to close inlet valve  16 , thereby preventing additional clean water from entering pre-washing chamber  12  from the clean water source. The water circulating in the circulation system is then used in a pre-washing operation, as discussed in detail above. 
     A second embodiment of the filter assembly will now be described with reference to  FIGS. 6-10 . Referring now to  FIG. 6 , there is shown a cross-sectional view of a filter assembly  270 , according to the second embodiment of the present invention. Similar to filter assembly  70 , filter assembly  270  is disposed between recirculation conduit  50  and return conduit  60 . Accordingly, filter assembly  270  is in fluid communication with recirculation conduit  50 , return conduit  60  and drain conduit  54 . 
     Filter assembly  270  is generally comprised a tubular housing  290 , a lower section  280  of return conduit  60 , and a filter element  320 . In the illustrated embodiment, housing  290  is comprised of a plurality of housing sections  290   a ,  290   b  and  290   c . Housing section  290   a  includes a side entry port  299  located at the upper end thereof, as best seen in  FIG. 7 . Side entry port  299  is in fluid communication with recirculation conduit  50 . Housing section  290   c  includes a funnel portion  298  to direct flow toward the center of housing  90 . Annular flanges  292  are formed at the upper and lower ends of housing section  290   a  and housing section  290   b , and are formed at upper end of housing section  290   c . An annular flange  282  also surrounds the outer surface of lower section  280  of return conduit  60 . 
     Conventional split ring clamps  110  are used to sequentially join lower section  280  of return conduit  60 , and housing sections  290   a ,  290   b  and  290   c . A first split ring clamp  110  joins annular flange  282  of lower section  280  to annular flange  292  at upper end of housing section  290   a . A second split ring clamp  110  joins annular flange  292  at lower end of housing section  290   a  to annular flange  292  at upper end of housing section  290   b . A third split ring clamp  110  joins annular flange  292  at lower end of housing section  290   b  to annular flange  292  at upper end of housing section  290   c.    
     Housing  290  and lower section  280  of return conduit  60  define an upper annular region  300 , while housing  290  and filter element  320  define an adjacent lower annular region  302 . Housing  290  also defines a collecting region  304 , wherein filtered solid debris is collected. 
     In the illustrated embodiment, filter element  320  includes a generally cylindrical wall  324  that extends downward from lower section  280  of return conduit  60 , as best seen in  FIGS. 6 ,  8  and  10 . Cylindrical wall  324  is generally coaxial with lower section  280  of return conduit  60 . The outer surface of cylindrical wall  324  is fixed to the inner surface of lower section  280  of return conduit  60  (e.g., by spot welding). Cylindrical wall  324  of filter element  320  defines a cylindrical chamber  332  having a closed end  326  and an open end  328 . Open end  328  of cylindrical chamber  332  is in fluid communication with lower section  280  of return conduit  60 . Perforations  330  are formed in cylindrical wall  324  to allow fluid to pass between lower annular region  302  and cylindrical chamber  332 . 
     Operation of filter assembly  270  will now be described in detail. Controller  14  transmits a control signal to move drain valve  58  to a closed position. Thereafter, the system can be primed with clean water in the same manner as described above in connection with the first embodiment of the present invention. 
     Water from conduit  50  enters upper annular region  300  through side entry port  299  formed in the side of housing section  90   a , as best seen in  FIG. 7 . The side entry into the upper annular region  300  causes the water to initiate a rotational flow, whereby the water flows along a downward spiral path inside filter assembly  270 , as best seen in  FIG. 6 . 
     As the water continues along the downward spiral path, the water moves into lower annular region  302 . Heavier solid debris, falls into collecting region  304 , and collects at the bottom thereof. Drain valve  58  prevents solid debris from passing into drain conduit. 
     As the water continues to flow in the direction of lower pressure in return conduit  60 , the water passes through perforations  330  of filter element  320  as it travels into cylindrical chamber  332  (see  FIGS. 8 and 9 ). Perforations  330  are dimensioned to block the passage of solid debris that is large enough to clog nozzles  64 . Water entering cylindrical chamber  332  continues traveling through return conduit  60  to lower and upper outlet portions  62   a ,  62   b . Accordingly, the recirculated water is released into pre-washing chamber  12  through nozzles  64 . Most of the lighter solid debris that is blocked by filter element  320  will eventually settle downward into collecting region  304 . 
     It is believed that the spiraling flow of the water within upper annular region  300  and lower annular region  302  will draw solid debris away from perforations  330 , thereby preventing solid debris from blocking or becoming lodged in perforations  330 . 
     Solid debris that collects in collecting region  304  of filter assembly  270  is periodically removed therefrom in a filter cleaning operation. In this regard, controller  14  transmits a control signal to move drain valve  58  to an open position. Accordingly, solid debris and water flow through drain conduit  54  into the drain (see  FIG. 10 ). Clean water may be pumped through filter assembly  270  while drain valve  58  remains open in order to flush out any additional solid debris remaining in filter assembly  270 . After the filter cleaning operation is completed, controller  14  transmits a control signal to move drain valve from an open position to a closed position. Some or all of the water removed from filter assembly  270  can then be replenished from the clean water source, such that there is a sufficient volume of water circulating in the circulation system for a pre-washing operation. 
     Other modifications and alterations will occur to others upon their reading and understanding of the specification. It is intended that all such modifications and alterations be included insofar as they come within the scope of the invention as claimed or the equivalents thereof.