Background.

This invention relates to a screen assembly for use in dishwashing machines.

Widely used known dishwashers generally have a closabie wash chamber in which dishes to be washed are placed in racks. A rotatable spray arm directs water at high velocity through several small openings in the spray arm to clean the dishes. The wash water carries food residue to the bottom of the machine where coarse particles are caught in a cup-like strainer and fine particles caught on a finely perforated substantially flat screen.

The fiat screen covers and generally encloses a sump, which is generally a tray-like structure extending across at least a substantial part of the base area of the chamber. The finely perforated screen covers the top of the sump and mates as closely as possible with a location ledge around the edges of the sump.

The foregoing type of filter screen arrangement has shortcomings. Food residue tends to clog the screen especially adjacent to the pump inlet. Also, the screen to sump fit is difficult to make sufficiently good in many designs to prevent residue particles from getting around the edges, so leading to blocking the jets in the spray arm.

Food residue or other objects, which can be on the screen or adjacent to it can be inadvertently spilled into the sump area during removal of the screen for cleaning. Residual water in the sump area hides the presence of these objects and they are often not removed before the machine is used again. Such objects, which may include small pieces of broken glass or china, small bones or small utensils, can then go through the pump and hydraulic system causing damage and blockages.

The present invention of a screen arrangement for a dishwasher seeks to overcome the abovementioned problems.

Summary of the Invention.

The invention consists of a removable screen arrangement for a dishwasher, the dishwasher being provided with a water pump and spraying system for removing food residues from articles to be washed and a tray like sump having a floor and walls for collecting the water and residues and wherein the screen arrangement comprises a hollow enclosure at least one finely perforated surface of which is configured to closely overlie a substantial proportion of said floor of the sump whilst being substantially uniformly spaced apart from it and wherein said finely perforated surface has formed on it spigot means to engage with a tube projecting upwardly from and fixed to the floor of the sump to engage with and locate said screen arrangement and wherein said tube forms a liquid communication between the interior of said hollow enclosure and an intake of said pump.

Preferably said hollow enclosure comprises one domed and one dished member, joined at their edges wherein the dished member is finely perforated.

Preferably the domed member is not perforated.

Preferably the spigot means is formed to closely fit the outside surface of the uppermost end of said tube.

Preferably the tube is finely perforated near its intersection with the floor of the sump.

Preferably the tube has at its top a coarse screen completely covering the end communicating with the interior of the hollow enclosure.

Preferably the sump has a separate outlet formed in the floor leading to a drainage means.

Preferably the outlet to the drainage means is provided with a strainer for trapping coarse objects.

Preferably the separate outlet to a drainage means is completely surrounded by a low weir projecting upwardly from the floor of the sump.

Preferably the strainer locates on the uppermost surface of the weir.

Brief Description of the Drawings.

The invention is explained in further detail by reference to an example of it as described in relation to a presently preferred form of it, including possible variations, as illustrated in the accompanying figure.

Detailed Description.

Figure 1 is a schematic cross-section to reduced scale of a screen assembly according to the invention.

Referring to Fig 1 the dishwasher filter is shown housed in a sump 10 which is located generally towards the bottom of a dishwashing machine (not illustrated) in which dishes and the like to be cleaned are held in racks above the sump.

Located within the sump is a removable filter unit, being a hollow enclosure 11 comprising a domed top plate 12 and a finely perforated dished bottom screen 14, sealed together around their mating peripheries by any suitable means such as clips or welding. The enclosure 11 is mounted low in the sump 10 with a gap between its periphery and the sump. The enclosure 11 is located a short distance above the floor 18 of the sump at the top of a short upstanding pipe 20 protruding through an opening in the sump floor 18.

An opening formed in the bottom screen 14 is formed to have a downwardly αirected spigot 19 to form a push-on fit onto the top end of the pipe 20.

The open lower end 22 of the pipe 20 is connected to a pump (not shown) which circulates water through the washing chamber during washing cycles via rotatable spray arms (not shown), thence by gravity to the sump.

The top end of the pipe 20 is fitted with a coarse screen 24.

The floor 18 of the sump has a second opening surrounded by a weir 26 in which is located a closely fitting coarse strainer 28 the opening being connected to a pump used for pumping water to the drain (not shown) at the end of the machine cycle. The strainer 28 is removable by hand for periodic cleaning.

In operation, food residue removed by washing from the dishes (not shown), including particulate residue, is carried by the wash water into the bottom of the sump 10. Water borne residue is prevented from entering the circulation pump by firstly being prevented from passing to the interior of the enclosure by contact with the bottom screen 14. Cap screen 24 provides a means of catching any objects which may enter pipe 20 whilst the screen is removed.

Cap screen 24 by being domed or of upwardly pitched-to-centre shape tends to shed any hard particles or large objects away from the pump inlet even if the dishwasher were to be incorrectly used without the hollow enclosure 11 portion of the filter in place.

Weir 26 surrounding the drain hole is capable of preventing hard heavy particles such as broken glass from passing into the drain outlet and hence the draining pump, since such particles are too heavy to be suspended in the water and carried over the weir 26.

Because spigot 19 can be formed in any suitable shape, ideally circular, to mate with pipe 20, its manufacture is simple and it is not subject to problems of distortion or otherwise difficult fit-up of known filters.

Domed top plate 12 may preferably have no perforations in which case the rood residue (which is normally unsightly by being visible adhering to the fine perforated filter at the bottom of the washing chamber in known dishwashing machines) is not visible.

However, domed top plate 12 may optionally be finely perforated, in which case the surface area of the filter may be substantially enlarged for given overall dimensions.

Waterborne particles drawn against the bottom screen 14 by the suction of the circulation pump during the wash cycle may fall off due to gravity during the drain cycle. This useful effect is further assisted by an inherent backwashing action of the filter since water in the filter enclosure 11 will run back into the sump at the conclusion of the wash and rinse cycles.

A further backwash effect may be achieved by providing an inlet which introduces clean water (when required for wash and rinse cycles) into the machine through the filter enclosure, either through pipe 20 or through a second spigot (not illustrated) in the bottom screen 14.

When the filter does require cleaning it may be simply lifted off pipe 6. Unlike known filters, this does not result in the likelihood of dislodging particles which could enter the circulation pump inlet and subsequently cause blockages in the jets of the spray arm. This is assisted by both the provision of the cap 24 and due to the spigot 19 fitting over the outside of the pipe 20.

The surfaces of the finely perforated screen 14 (and plate 12 if it is also perforated) may be rippled or ridged to discourage particles of food residue sticking to the screen or plate due to the formation of a film of water between the residue and the screen surface.

The upstanding pipe 20 and weir 26 may be perforated at the level of the sump floor 18 to encourage complete draining of the sump when the machine is not in use. This facilitates the cleaning of the sump at the time of cleaning the filter unit and hence the avoidance of decomposition of food residue in the sump, so avoiding the machine's washing chamber developing unpleasant odours if left unused for a period of some days.