Filter screen with backflush

A filter screen assembly is provided which includes a housing, a filter screen, and two valve or check balls. The housing has two interior walls, each having openings therein which divide an interior space of the housing into top, center, and bottom chambers. A first inlet and a first outlet open into the top chamber and a second inlet and a second outlet open into the bottom chamber. The filter screen is horizontally disposed within the center chamber. One check ball is located in the top chamber and is biased to close the first inlet by a bottom inclined surface of the top chamber. The check ball is forced to substantially close the first outlet when fluid flows in the first inlet. The other check ball is located in the bottom chamber and is biased to close the second inlet by a bottom inclined surface of the bottom chamber. The check ball is forced to substantially close the second outlet when fluid flows in the second inlet. The filter screen thereby filters fluid entering the first inlet and exiting the second outlet and is automatically cleaned or backflushed by fluid entering the second inlet and exiting the first outlet.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally relates to a filter screen assembly, and 
more specifically, a filter screen assembly for a dishwasher that filters 
soil from wash or rinse water and is automatically backflushed by drain 
water. 
2. Description of Related Art 
Domestic or household dishwashers generally consist of an enclosed cabinet 
having a bottom hinged door at the front of the cabinet for closing off an 
otherwise sealed washing chamber or tub. Dishes are placed on upper and 
lower racks which are arranged to slide or roll in and out of the tub when 
the door is open. The dishwashers typically have a rotating lower wash arm 
which rotates and carries a number of spray openings which direct water 
upward as the arm rotates to spray all of the dishes in the tub. 
Additionally, some dishwashers have an upper wash arm located above the 
lower rack and below the upper rack to provide additional washing ability. 
Furthermore, some dishwashers have an upper wash arm beneath the top wall 
of the tub to spray water down on all the dishes in the tub. 
The dishwashers typically operate with alternating wash and rinse cycles in 
which the wash cycle is distinguished only by length of time and the fact 
that detergent has been added to the water. During each cycle, the water 
is drawn from a sump at the bottom of the tub and passes through a pump to 
the wash arms. The water passes over the dishes in the racks and returns 
to the sump. After each wash or rinse cycle is a drain cycle for removing 
the fluid within the sump so that it can receive fresh water. 
A problem with all types of dishwashers is handling soil particles removed 
from the dishes being washed. As the soil particles are washed off the 
dishes, they pass into the water in the sump, are drawn into the pump with 
the water, and are recirculated through the wash arms. Therefore, the soil 
particles can be redeposited on the very dishes from which they were 
removed. Some soil particles are removed by a screen in the sump. Most of 
the soil particles pass through the screen, however, because the screen 
must be relatively coarse so that it does not become clogged. 
In the case of dishwashers having separate drain and recirculation pumps, 
the solution to this problem has been to provide a collector or filter 
screen arranged such that the water passes through the filter screen in 
the recirculating cycles prior to entering the recirculation pump to 
remove the soil particles. The filter screen is automatically cleaned by 
water going to the drain from the drain pump during the drain cycle. 
In the case of dishwashers having a single unidirectional pump, the 
solution to this problem has been to provide the pump with a macerator or 
cutting blade to break up the soil particles as they are recirculated 
until they become sufficiently fine to be less likely to be redeposited on 
the dishes. Alternatively, a filter screen is provided between the pump 
and the upper spray arm so that filtered water will wash or rinse any soil 
particles off the dishes even if such soil particles have been redeposited 
on the dishes by the lower spray arm. The filter screen is automatically 
cleaned by water going to the drain from the pump during the drain cycle. 
SUMMARY OF THE INVENTION 
The present invention provides an improved self-cleaning filter screen 
assembly. The filter screen assembly includes a housing, a filter screen, 
and first and second valve means. The housing has an interior, first and 
second inlets, and first and second outlets. The filter screen is located 
in the housing and divides the interior into first and second interior 
portions. The first inlet and the first outlet open into the first 
interior portion and the second inlet and the second outlet open into the 
second interior portion. The first valve means substantially closes the 
first inlet to generally prevent fluid flow out of the first inlet and is 
operable to substantially close the first outlet when fluid flows in the 
first inlet. The second valve means substantially closes the second inlet 
to generally prevent fluid flow out of the second inlet and is operable to 
substantially close the second outlet when fluid flows in the second 
inlet. The filter screen thereby filters fluid entering the first inlet 
and exiting the second outlet and is automatically cleaned or backflushed 
by fluid entering the second inlet and exiting the first outlet.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 illustrates portions of a dishwasher 10 relevant to an understanding 
of the construction and operation of the present invention. The dishwasher 
10 has a tub 12 with an open front 14 which is normally closed by a door 
(not shown) hinged along the lower side and latched at the top. The tub 12 
is formed by a pair of spaced apart side walls 16, 18, a back wall 20 
which connects the side walls 16, 18, a top wall 22 which closes off an 
upper side of the tub 12, and a bottom wall 24 which closes off a lower 
side of the tub 12. The bottom wall 24 is formed into a sump 26, which is 
generally depressed from a planar surface and sized to accommodate a 
desired volume of wash water without having the water flow through the 
open front 14. The dishwasher 10 is supported on a pair of base legs 28, 
30 which are connected in a suitable manner to the tub 12 and serve to 
space the tub 12 above the floor to provide sufficient space for operating 
mechanisms of the dishwasher 10. 
Below the sump 26 is mounted a pump 32 driven by an integrally mounted 
electric motor 34. The pump 32 is generally of the centrifugal type, and 
has an inlet 36 16 connected to an inlet fitting 38 located toward the 
rear of the lowest portion of the sump 26. The pump 32 has a first spray 
arm port or outlet 40 connected to a main or lower spray arm 42. The lower 
spray arm 42 has suitable openings for directing a spray of water at the 
contents of the tub and for causing the lower spray arm 42 to rotate by a 
reaction force as it sprays. The pump 32 also has a drain port or outlet 
44 and, above that, a second spray arm port or outlet 46. 
Although the pump 32 is not shown or described in detail, it should be 
understood that the pump 32 may be constructed in a known manner. The pump 
32 typically has a diverter valve (not shown) which can be actuated 
between a first position during the wash mode and a second position during 
a drain mode. In the first position, the diverter valve blocks off the 
drain outlet 44 and directs water flow through the first and second spray 
arm outlets 40, 46. In the second position, the diverter valve 
substantially blocks off flow to the first and second spray arm outlets 
40, 46 and directs substantially all of the water flow through the drain 
outlet 44. 
A filter screen assembly 48 according to a preferred embodiment of the 
invention is mounted adjacent one of the base legs 28 and generally facing 
the pump 32. Located on a side of the filter screen assembly 48 facing the 
pump 32 is a first or drain inlet 50 on an upper portion and a second or 
spray arm inlet 52 on a lower portion. A drain hose 54 connects the pump 
drain outlet 44 to the drain inlet 50 of the filter screen assembly 48. A 
suitable hose 56 also connects the pump second spray arm outlet 46 with 
the spray arm inlet 52 of the filter screen assembly 48. Located on an 
opposite side of the filter screen assembly 42 is a first or spray arm 
outlet 60 on the upper portion and a second or drain outlet 58 on the 
lower portion. The drain outlet 58 of the filter screen assembly 48 is 
connected to a high loop tube 62 to prevent back flow, which in turn, at 
its other end, has an outlet 64 to be connected to a household sewer 
drain. A suitable tube 66 connects the spray arm outlet 60 of the filter 
screen assembly 48 to a second or upper spray arm 68. The upper spray arm 
68, like the lower spray arm 42, has suitable openings for directing a 
spray of water at the contents of the tub and for causing the upper spray 
arm 68 to rotate by a reaction force as it sprays. 
Construction and operation of the filter screen assembly 48 can be more 
easily understood with reference to FIGS. 2-4. The filter screen assembly 
48 includes a shell or housing 70, a filter screen 72, and a pair of check 
balls 74, 76. The housing 70 is preferably formed in two halves from a 
suitable plastic material such as polypropylene. The two halves of the 
housing 70 are secured together, with the filter screen 72 and check balls 
74, 76 in place, by a suitable means such as heat sealing or ultrasonic 
welding. 
The housing 70 has two interior walls 78, 80 which divide an interior 
cavity of the housing 70 into three chambers 82, 84, 86. The first or 
upper interior wall 78, along with exterior walls 88 of the housing 70, 
form the first or top chamber 82 in an upper portion of the housing 70. 
The drain inlet 50 and the upper spray arm outlet 60 are located at 
opposite ends of the top chamber 82 and each open into, that is, are in 
fluid communication with, the top chamber 82. The second or center chamber 
84 is formed by the interior walls 78, 80, along with the exterior walls 
88, in a central portion of the housing 70. The second or lower interior 
wall 80 forms, along with the exterior walls 88, the third or bottom 
chamber 86 in an upper portion of the housing 70. The spray arm inlet 52 
and the drain outlet 58 are located at opposite ends of the bottom chamber 
86 and each open into, that is, are in fluid communication with, the 
bottom chamber 86. 
A valve or ball seat 90 is located at each interface between the respective 
inlets 50, 52, outlets 58, 60, and chambers 82, 86. The ball seats 90 are 
adapted to generally seal the interface, that is, substantially block 
fluid communication through the interface, when a respective one of the 
check balls is seated thereon. The check balls 74, 76 are preferably 
formed from a suitable plastic such as polypropylene and are sized for 
engagement with the ball seats 90. 
The filter screen assembly 48 also includes means for biasing the check 
balls 74, 76 to the ball seats 90 associated with the inlets 50, 52. The 
biasing means of the illustrated embodiment includes inclined or sloping 
bottom walls of the top and bottom chambers 82, 86 which support the check 
balls. The check balls 74, 76 are forced by gravity to roll or slide down 
the inclined walls to the ball seats 90 the respective inlets 50, 52, as 
shown in FIG. 2. The bottom walls of the top and bottom chambers 82, 86 
are formed such that check balls 74, 76 are biased to the ball seats 90 
associated with the inlets 50, 52. A flow of water through either of the 
inlets 50, 52, however, overcomes the bias to force the respective check 
ball 74, 76 to the ball seat 90 of the associated outlet 58, 60. 
Formed generally at the center of the housing 70 is an internal groove 92 
adapted for sealingly receiving a frame 94. Molded within the frame 94 is 
a filter screen 96. The filter screen 96 is preferably of a fine mesh 
suitable for filtering soil particles from wash water. Mounted in this 
fashion, the filter screen 96 is generally horizontally disposed and 
divides the center chamber into upper and lower portions 84a, 84b. 
The upper interior wall 78 includes a plurality of openings or apertures 98 
such that the upper chamber 82 opens into, that is, is in fluid 
communication with, the upper portion 84a of the center chamber 84. The 
openings 98 are preferably located near the upper spray arm outlet 60. The 
lower interior wall 80 also includes a plurality of openings or apertures 
100 such that the lower chamber 86 opens into, that is, is in fluid 
communication with, the lower portion 84b of the center chamber 84. The 
openings 100 are preferably located near the drain outlet 58. 
Operation of the filter screen assembly 48 is best seen in FIGS. 2-4. When 
the dishwasher is in an idle mode, the check balls 74, 78 are forced 
against the ball seats 90 associated with the inlets 50, 52, as shown in 
FIG. 2. When the dishwasher is in a wash mode, a flow of water from the 
pump passes through the upper spray arm inlet 52 and enters the bottom 
chamber 86 as shown in FIG. 3. The flow of water upwardly forces the check 
ball 76 in the bottom chamber 86 to the ball seat 90 associated with the 
drain outlet 58. The flow of water is substantially blocked by the check 
ball 76 from passing to the drain outlet 58 and passes through the 
openings 100 of the lower interior wall 80 from the bottom chamber 86 to 
the lower portion 84b of the center chamber 84. In the center chamber 84 
the flow of water passes through the filter screen 96 from the lower 
portion 84b to the upper portion 84a and deposits any carried soil 
particles on the lower side of the filter screen 96. The flow of water 
passes through the openings 98 of the upper interior wall 78 from the 
upper portion 84a of the center chamber 84 to the top chamber 82. The flow 
of water is substantially blocked by the check ball 74 from passing to the 
drain inlet 50 and passes through the upper spray arm outlet 60 from the 
top chamber 82 to the upper spray arm. At the end of the wash mode, the 
flow of water through the upper spray arm inlet 52 substantially stops and 
the check ball 76 in the lower chamber 86 is again biased to the ball seat 
90 associated with the upper spray arm inlet 52 as shown in FIG. 2. 
When the dishwasher is in a drain mode, a flow of water from the pump 
passes through the drain inlet 50 and enters the top chamber 82 as shown 
in FIG. 4. The flow of water upwardly forces the check ball 74 in the top 
chamber 82 to the ball seat 90 associated with the upper spray arm outlet 
60. The flow of water is substantially blocked from passing to the upper 
spray arm outlet 60 and passes through the openings 98 of the upper 
interior wall 78 from the top chamber 82 to the upper portion 84a of the 
center chamber 84. In the center chamber 84 the flow of water passes 
through the filter screen 96 from the upper portion 84a to the lower 
portion 84b and flushes away any accumulated soil particles on the lower 
side of the filter screen 96. The flow of water, with the soil particles, 
passes through the openings 100 of the lower interior wall 80 from the 
lower portion 84b of the center chamber 84 to the bottom chamber 86. The 
flow of water is substantially blocked from passing through the upper 
spray arm inlet 52 and passes through the drain outlet 58 from the bottom 
chamber 86 to the household sewer drain. At the end of the drain mode, the 
flow of water through the drain inlet 50 stops and the check ball 74 in 
the upper chamber 82 is again biased to the ball seat 90 associated with 
the drain inlet 50 as shown in FIG. 2. 
It will therefore be seen that the filter screen assembly 48 functions to 
filter soil particles from water delivered to the upper spray arm 68 
during the wash mode and to automatically back flush any accumulated soil 
particles from the filter screen 96 during the drain mode to avoid any 
build-up and/or clogging of the filter screen 96. Although particular 
embodiments of the invention have been described in detail, such as 
operation in a dishwasher having a unidirection pump, it will be 
understood that the invention is not limited correspondingly in scope, but 
includes all changes and modifications coming within the spirit and terms 
of the claims appended hereto.