Abstract:
A dishwasher having a cabinet and wash chambers in the form of drawers which slide in and out of the cabinet. Rigid and flexible closures are disclosed for sealing off the wash chambers when retracted into the cabinet. A detergent dispenser for the dishwasher is provided in one wall of a wash chamber in the wash water discharge path into the wash chamber so that detergent powder is flushed out of the dispenser and mixed with the wash water prior to the latter being discharged into the wash chamber. 
     A wash program for a dual wash chamber dishwasher is also disclosed which minimizes total water consumption by transferring water from one chamber to the other.

Description:
This is a divisional of application Ser. No. 09/020,580 filed on Jan. 30, 1998, now U.S. Pat. No. 6,189,551. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to dishwashers and in particular but not solely to a dishwasher of the type disclosed in the applicant&#39;s international patent specification WO 93/12706. 
     PRIOR ART 
     The dishwasher of WO 93/12706 has a form generally indicated in FIGS. 1 and 2 and installation options as shown in FIGS. 4 to  6 . The dishwasher disclosed in WO 93/12706 differs from conventional dishwashers in that a wash chamber and associated wash system is slidably mounted in the form of a drawer within a cabinet and the chamber is withdrawn horizontally to allow loading through the open top of the chamber. When the chamber is retracted an associated lid sealably closes off the top of We chamber to contain wash liquid in operation. In WO 93/12706 the wash chamber lid is of unitary conduction movably retained in the top of the cabinet and is engaged-by the wash chamber on retraction to move down onto the top of the wash chamber using a parallelogram linkage and can mechanism In practice it has been found that other types of wash chamber covers may be satisfactorily and may have better production economics. 
     Detergent dispensers are a necessary component of all dishwashers. Conventional dispensers retain a charge of detergent until an appropriate point in the wash cycle, at which time a detergent receptacle opens to release detergent into the wash chamber. Conventional dispensers have the disadvantage that considerable quantities of high pressure liquid need to enter the detergent receptacle to ensure it is properly flushed and where the receptacle uses a moving door to release the detergent, the opening of the door can be obstructed by the wash load. 
     In the previously mentioned WO 93/12706 a dishwasher drain pump was disclosed. While the drain pump there described operated satisfactorily, particles in the soiled wash water could be deposited in the gap between the motor rotor and well  106 . 
     In WO 93/12706 a dishwasher was disclosed having a cabinet containing single wash chamber and associated wash system. Because a sliding drawer type configuration exerts more forces on the cabinet than front loading machines portal fame members were proposed to increase the racking resistance of the cabinet. In WO 93/12706 it was envisaged that increased dishwashing capacity could be achieved by simply increasing the number of discrete dishwasher modules. Particular reference was made to mounting two modules under a kitchen bench one above he other. The height of each module was chosen to ensure that when two modules were mounted in the kitchen joinery one above they other they would fit within the bench height of typical household kitchens. In some circumstances an integral two wash tub dishwasher may be preferred—that is, a cabinet having two drawers instead of one. This however increases the problem of providing adequate resistance to racking forces exerted by the wash tubs since the ‘open’ fronted cabinet is then required to be approximately twice the height of a single drawer cabinet. 
     SUMMARY OF INVENTION 
     It is an object of the present invention to provide a dishwasher of the type described having an effective wash chamber closure sealing system. 
     It is a further object of the present invention to provide a dishwasher detergent dispenser which at least goes some way towards overcoming the above-mentioned disadvantages. 
     Further objects of the invention are to provide: 
     a dishwasher with an improved drain pump, 
     a dishwasher cabinet for housing two wash chambers, 
     a dishwasher water management system, and 
     a heating element fault protection circuit. 
     In one aspect the present invention consists in a washing appliance comprising: 
     (a) a cabinet, 
     (b) a wash system slidably mounted wit said cabinet in such a manner that it may be withdrawn horizontally out of said cabinet for access thereto, said wash system including: 
     (i) an open top wash chamber adapted to accommodate dishes within which wash liquid is circulated, said wash chamber hang a top peripheral rim, 
     (ii) means for introducing and circulating wash liquid within said chamber, 
     (iii) means for evacuating wash liquid from said chamber, 
     (c) a wash chamber closure mounted in the top of said cabinet, which closure covers the open top of said wash chamber on retraction of the wash chamber into said cabinet, 
     (d) said closure having peripheral means which cooperate with said rim to prevent egress of wash liquid from the wash chamber when it is retracted into said cabinet, and said closure being retained in a substantially fixed vertical position in the top of said cabinet. 
     In a further aspect the invention consists in a washing appliance comprising: 
     (a) a cabinet, 
     (b) a wash system slidably mounted within said cabinet in such a manner that it may be withdrawn horizontally out of said cabinet for access thereto, said wash system including: 
     (i) an open top wash chamber adapted to accommodate item to be washed and within which wash liquid is circulated, said wash chamber having a top peripheral rim, 
     (ii) means for introducing and circulating wash liquid within said chamber, 
     (iii) means for evacuating wash liquid from said chamber, 
     (c) a wash chamber closure mounted in the top of said cabinet, which closure covers the open top of said wash chamber on retraction of the wash chamber into said cabinet, 
     (d) said closure being mounted in the top of said cabins by mechanical means which permit it to move in a vertical direction only and said closure having peripheral means which cooperate with said rim to prevent egress of wash liquid from the wash chamber when it is lowered from a raised position; and 
     (e) means for raising said closure prior to withdrawal if the wash system from the cabinet and lowering said closure on retraction of said wash system into said cabinet. 
     In a further aspect the invention consists in a dishwasher, including a detergent dispenser mounted in one interior wall thereof and a controller which controls the sequence of operations executed by said dishwasher, 
     said detergent dispenser comprising: 
     receptacle located behind said wall and communicating with the dishwasher interior through a vent in said wall, 
     an open top container for holding a charge of detergent mounted with said chamber, 
     a water outlet nozzle positioned above the open top of said container, and a supply valve which supplies water to said nozzle, 
     said controller causing said valve to open at a predetermined time in said cycle to cause water to be discharged from said nozzle into said container to mix with and flush said detergent charge through said vent into the interior of said dishwasher. 
     In yet a further aspect the present invention consists in a washing appliance according to claim  13  wherein said lid is mounted in the top of said cabinet so as to lower when the wash chamber is retracted and raise when the wash chamber is withdrawn, the edge of said lid is provided with downward facing flanges and the rim of said wash chamber is provided with complementary upward facing flanges, the lid and rim flanges loosely inter-engaging when the lid is lowered to form a labyrinthic seal there between. 
     In yet a further aspect the present invention consists in a cabinet for a dishwasher having a box configuration with one open side and including a recessed kick plate along the bottom of the open side which cabinet provides resistance to racking forces applied parallel to the open side comprising: 
     a top, bottom, two side walls and a back wall of thin sheet material joined along their edges to leave a substantially rectangular front opening defined by the front edges of the top, bottom and two side walls, 
     the front edge of the bottom wall and the lowermost portions of the side walls being co-planar and recessed back from the front edges of the top wall and the upper portions of the side walls which lie in a second plane, 
     internally directed flanges on said front edges, 
     said flanges on the bottom and bottom side contiguous edges being rigidly joined at the two bottom corners and thereby configured as an inverted tapered beam portal frame with said two corners forming moment resisting joints, 
     rigid link members coupling the flanges on the lower recessed portions of the side walls to said flanges on the upper portions of the side walls mid the flange on the top edge forming a beam linking the tops of the flanges on the upper portions of the side walls, the two joints defined by the intersections of the beam with the portal fame having no substantial resistance to bending moments. 
     In yet a further aspect the present invention consists in a dishwasher having a wash progamme consisting of pre-rinse, wash, first post rinse and second post rinse cycles comprising: 
     first and second wash chambers, 
     means for transferring wash liquid from the first wash chamber to the second wash chamber, and 
     a controller which implements said wash programme and which controls the operation of said transference means, 
     said controller; 
     (a) delaying the commencement of the wash programme for said second wash chamber until after the end of the first post rinse cycle in the wash programme for the first wash chamber, 
     (b) causing said transference means to transfer the rise water from the fist post rinse cycle of the first wash chamber from the fist wash chamber to the second wash chamber, 
     (c) initiating the pre-rinse cycle for the second wash chamber using the first post rinse water from the first wash chamber, 
     (d) causing said transference means to transfer the rinse water from the second post rinse cycle of the first wash chamber from the first wash chamber to the second wash chamber, and 
     (e) initiating the wash cycle for the second wash chamber using the second post rinse water from the first wash chamber. 
     In yet a further aspect the present invention consists in a dishwasher comprising: 
     (a) a wash chamber adapted to accommodate dishes within which wash liquid is circulated, 
     (b) a cylindrical well provided in the floor of said chamber, 
     (c) an electric motor including: 
     (i) a rotor mounted within said well and 
     (ii) a co-acting stator mounted outside said wash chamber about the exterior surface of said well such that the cylindrical sides of said well lie in the rotorstator air gap, 
     (d) a drain pump impeller mounted on the rotor drive shaft in the well below the rotor, 
     (e) a sump formed in the floor of said wash chamber which is connected to the lower side wall of said well which houses said impeller by a conduit, 
     (f) a discharge tube connected to a different point about the surface of the lower side wall of said well which houses said impeller, 
     (g) said drain pump impeller comprising a disc, the periphery of which is closely adjacent to the side wall of said well to form a seal against fluid flow up the side of said well, said disc having a hub portion and blades formed on the lower surface thereof with the toot of each blade radially spaced from the periphery of the hub portion to form an unimpeded annular fluid passage between the hub portion and the blades. 
     In yet a further aspect the present invention consists in a protection circuit for a resistive heating element powered from an alternating current supply comprising: 
     a current transformer the primary circuit of which comprises both the phase and neutral supply conductors connected across said heating element, 
     a secondary transformer winding across which a voltage is developed which is proportional to any out of balance current between the phase and neutral conductors respectively, 
     a third conductor forming a tertiary transformer circuit which is arranged to carry a very low bias current derived from said alternating current supply and to continuously develop a small predetermined voltage in the transformer secondary winding, 
     a direct current supply derived from said alternating current supply, 
     a relay coil and a transistor series connected across said direct current supply, the relay switch being connected in series with one of the alternating current supply conductors to the heating element, 
     a voltage sensing means connected to said secondary winding which provided said predetermined voltage is present across the secondary winding supplies enough current to said transistor to cause it to conduct sufficiently to allow a current to flow through said relay coil from said direct current supply which is sufficient to hold the relay switch on and to present an alternating voltage across said beating element, but in the event of failure to detect said predetermined voltage said voltage sensing means supplies insufficient current to said transistor to allow it to conduct enough current through the relay coil to retain the relay latched on. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows in diagrammatic form a dishwasher of the present invention, 
     FIGS. 2 and 3 shows in diagrammatic form the dishwasher plumbing and wiring system with the wash chamber in the closed and open positions respectively, 
     FIGS. 4 to  6  show a selection of ways in which dishwashers of the type in WO 93/12706 and in the present specification may be mounted in a modular ashion in a kitchen installation, 
     FIG. 7 shows a ‘two drawer’ single cabinet dishwasher according to the present invention, 
     FIG. 8 shows the structural features of the cabinet of FIG. 7, 
     FIGS. 9 and 10 show in diagrammatic form a means of sealing an open top wash chamber with a rigid lid using an inflatable gasket, 
     FIG. 11 shows a partial section through a dishwasher incorporating the sealing method shown in FIGS. 9 and 10, 
     FIG. 12 shows in diagrammatic form one means of juxtapositioning the gasket ends to minimise leakage, 
     FIG. 13 shows a partial isometric drawing of a dishwasher wash chamber with lid and a sealing gasket as shown in FIG. 11, 
     FIG. 14 shows a further method of sealing an open topped wash chamber using a rigid lid, 
     FIG. 15 shows a method of sealing an open topped wash chamber using a flexible closure member, 
     FIGS. 16 and 17 show an alternative method of scaling an open topped wash chamber using a flexible closure, 
     FIGS. 18 and 19 show diagrammatically a further method of sealing an open topped wash chamber with a rigid lid, 
     FIGS. 20 and 21 show an alternative method of sealing all open topped wash chamber with a rigid lid, 
     FIGS. 22 and 23 show diagrammatically a further method of sealing an open topped wash chamber with a rigid lid, 
     FIG. 24 shows a dual tub dishwasher with provision for inter-tub water transfer. 
     FIG. 25 shows a partial cross-section of a dishwasher drain pump, 
     FIG. 26 shows an isometric underside view of the drain pump impeller, 
     FIG. 27 shows a dishwasher heating element, 
     FIG. 28 shows a cross-section along line A—A on FIG. 28, 
     FIG. 29 shows a dishwasher heating clement protection circuit, 
     FIG. 30 shows a dishwasher detergent dispenser open for filling, 
     FIG. 31 shows the dishwasher detergent denser of FIG. 30 closed for use, 
     FIG. 32 shows a pictorial view of the detergent dispenser open for filling, 
     FIG. 33 shows a partial cross-section of the detergent dispenser, 
     FIG. 34 shows a plan view of the detergent dispenser closed, 
     FIG. 35 is a partial view of the detergent dispenser showing how it is fixed to the dishwasher wall, 
     FIG. 36 shows a sectional view of a dishwasher detergent dispenser indicating water paths through the dispenser, 
     FIG. 37 shows a pictorial sectional view of a two-way shuttle valve for use with a dishwasher detergent dispenser, 
     FIG. 38 shows a diagrammatic view of an alternative construction for closing a wash chamber when a fixed lid is used, 
     FIG. 39 shows a diagrammatic view of an alternative construction for closing a wash chamber when a fixed lid is used by making use of a moveable seal support carrier, 
     FIG. 40 shows a diagrammatic cross-section of a wash chamber and associated lid which is lowered to close the wash chamber by a stored spring energy system, 
     FIG. 41 shows a partial isometric cross-section of the mechanism illustrated in FIG. 40, 
     FIG. 42 shows diagrammatically yet a further alternative closure system for a wash chamber using an endless belt, 
     FIGS. 43 and 44 show supplementary sealing members for a wash chamber closure, 
     FIGS. 45 to  47  show diagrammatically a wash chamber closure system employing a spring loaded cam and cam follower lid lowering mechanism. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present dishwasher  200  is of the type illustrated in FIG. 1. A wash chamber  201  (with all wash system components) fitted with a front panel  202  is slidably mounted within a cabinet  203  in a ‘drawer’ arrangement. The wash chamber has an open top and is withdrawn from the cabinet in the direction of the arrow to allow loading and unloading of dishes and is retracted into cabinet  203  during washing. The wash and drain systems are fitted within wash chamber  201  including a motor and pumps. Flexible connecting wiring and plumbing  228  couple the wash chamber to the relevant terminations within the cabinet in the manner indicated in FIGS. 2 and 3. The dishwasher controller may be mounted in the cabinet or in tile sliding wash system. 
     The dishwasher is usually constructed with a height dimension approximately half that of conventional front-loading domestic dishwashers. In this form it can be used alone or as one of a number, more usually one of a pair of such dishwashers. FIGS. 4 to  6  show installation concepts using one or two dishwashers using this modular concept. In FIG. 4, two such dishwashers  200  arc shown stacked one above the other under a sink bench  1  which will typically be between 850 and 900 mm above floor level. In FIG. 5 two dishwashers  200  are shown mounted one on either side of a sink forming part of the sink bench  1 . In FIG. 6 only a single dishwasher  200  is provided under a sink bench  1 . Because of the reduced height dimension a dishwasher according to the invention could also be bench mounted. 
     From FIG. 4 it can be seen that when two modular dishwasher units  200  are stacked one above the other the configuration is similar in external dimensions to conventional dishwashers. Two modular units  200  installed side by side immediately under a bench top as in FIG. 5 offer the same capacity as a conventional dishwasher but avoid the inconvenience of a user having to bend down to reach the lower half of the dishwasher. 
     Some pair arrangements could be manufactured as such rather than pairing two individual modules at installation. For example the two dishwasher ‘over and under’ configuration shown in FIG. 4 can be manufactured in a single external envelope or cabinet and provided for installation as a unitary machine. Such a two drawer machine is shown in FIG. 7, comprising a single cabinet  203  which houses two drawer type wash chambers  202   a  and  202   b . The drawer fronts are each provided with an aesthetically pleasing facia. 
     A two drawer machine of this type allows for considerable flexibility in operating modes. These include: 
     1. One module operating, or two modules operating simultaneously with a mixed dish load. With each module capable of accommodating the largest item of dish load, this concept offers an increased capacity for large items. 
     2. One or both modules operating, but not necessarily simultaneously, where each module has either lightly soiled or heavily soiled dish load, and the appropriate wash programme set to suit the individual module. 
     3. One module being gradually filled with soiled dishes, while the second module is being emptied only as its clean dish load is being reuses For reasons of hygiene this is not practical with single dishwashers. 
     4. One module programmed for lightly soiled loads and the other module for heavily soiled loads. 
     5. One module switched on as soon as it has been filled with soiled dishes. That is, smaller loads may be efficiently washed. 
     Cabinet 
     FIG. 8 shows some of the structural features of the cabinet  203  of FIG.  7 . Cabinet  203 , which would normally be made from sheet steel, has the form of an open-sided box with top and bottom panels  205  and  206 , two side walls  207  and a rear wall (not shown). The front of the cabinet is open except for a shallow kick plate  62  which is recessed back from the principal plane of the front of the cabinet and a transom member  63 . The open front of cabinet  203  is stiffened to resist lateral racking forces by the provision of portal frame members  63  and  64  as described in WO 93/12706. In the present form the front edge flanges on the bottom  66  and side walls  208  and flanges  65  of member  63  are configured as two portal frames. The first portal frame is formed by member  64 , side flanges  208  and transom member  63 , which are joined together by joints having no moment resisting capacity. Therefore, member  63  effectively forms a beam to tie together the portal member  64  and sides  207 . The second portal frame is formed by member  63 , side flanges  271  and the front flange section  272  of the top wall  205 . Again, flange section  272  effectively forms a beam to tie together the portal member  63  and sides  271 . The bottom of each of the two wash chambers  202   a  and  202   b  is configured to pass over the upper flanges  65  and  66  of portal frame members  63  and  64  respectively. However, unlike the portal frame for the upper opening (and unlike the cabinet shown in WO 93/1206) portal frame member  64  is offset rearwardly from the principal plane of the front of cabinet  203  and its effectiveness in resisting racking moments on the bottom half of cabinet  203  is reduced. This is overcome in the present invention by providing reinforcing plates  67  and  68  at the top of kick plate  62  and structurally tying these plates together through the lower wash chamber slide members (not shown) which are located in positions  69  and  70  indicated in broken lines. Plates  67  and  68 , because of their rigidity and rigid connections to the bottom frame  64  and the side frames  208 , respectively transfer racking forces applied to the side frames to the gusset areas  209  at each end of the bottom frame  64 . In the preferred form of the present invention the reinforcing plates  67  and  68  are fish plates. 
     Closure for Sliding Drawer Wash System 
     In a washing machine as proposed here, where the wash chambers are mounted as sliding drawers, the closing of the chambers prior to commencement of the wash cycle is more complicated with conventional front loading or above-bench top loading machines. It is undesirable to have users manually close a door to seal the open-topped wash chamber prior to pushing the extended ‘drawer’ back into the cabinet. It is preferable to have a closure which is actuated by the action of retracting the wash chamber back into the cabinet 
     In FIG. 1, a rigid closure or lid  217  is diagrammatically shown which is mounted in the top of the cabinet  203  for closing the open top of wash chamber  201 . Closure can be effected by mounting the lid in such a way as to allow it to be mechanically forced downwardly on to the rim of wash chamber as the chamber is retracted into cabinet  203 . One means for achieving this type of sealing action is disclosed in WO 93/12706. In contrast to moving a rigid lid in both the horizontal and vertical directions by mechanical linkages in a parallelogram fashion to a sealing position during the last portion of travel of the wash chamber, the present invention provides alternative solutions. 
     The first of these is illustrated diagrammatically in FIGS. 9 and 10. In this case a rigid lid  217  is used as previously described, but is fixed in position in the top of cabinet  203  and fitted with a peripheral inflatable gasket  18  located in vertical registration with rim  19  of wash chamber  201 . In this embodiment when the wash chamber is fully retracted, member  18  is inflated as shown in FIG. 10 to sealably engage with rim  19 . In this case member  18  is the sealing member, but an equally suitable alternative would be to inflate a sealing member carrier  250  interposed between the lid and sealing member  251  as shown in FIG.  38 . 
     A practical realisation of this embodiment is shown in more detail in FIGS. 1 and 13. Wash chamber  201  is formed with a flanged rim  19  which in use provides a seat for inflatable gasket  18 . In FIG. 11 washtub  201  is indicated as being fully retracted within cabinet  3  with gasket  18  being inflated so as to sealably engage rim  19 . 
     A rigid lid  217  is fitted into the top of cabinet  203  and a peripheral abutment  30  on lid  217  bears against the underside of the top of cabinet  3 . Lid  217  is essentially fixed in relation to cabinet  203 . It is provided at the periphery of its underside with a channel  31  for retaining gasket  18 . 
     Gasket  18  is moulded from an elastic plastics material and is formed as an indefinite length. A ribbed extension  32  is integrally moulded oil the top surface of the gasket to engage in channel  31  in lid  217  to thereby engage the gasket to the lid. 
     In one embodiment (not shown) a length of gasket material  18  sufficient to trace out periphery of lid  17  is fitted in place and each end coupled to opposite connections on a T connector. The T connector provides air to both ends of gasket  18  to inflate it when required. In a preferred embodiment diagrammatically shown in FIG. 12, a length of gasket material sufficient to allow the ends  37  and  38  to overlap is employed. The channel  31  in the lid also has overlapping parallel ends to support the gasket ends in close parallel relationship. End  37  of gasket  18  includes an air-tight stopper  39  (or is otherwise sealed) while end  38  contains a connector  40  for an air hose  41  which supplies air to inflate the gasket. 
     Even when the gasket is inflated a small amount of wash fluid will leak between the overlapping ends of the gasket during the wash cycle of the dishwasher. Water egress through this gap must be controlled and for this purpose drainage slots  42  are provided in the wash chamber rim  19  in the region of the exterior gasket end  38  (see also FIG.  13 ). Any water escaping between the gasket ends is diverted through the slots into a ducting  36 . Ducting  36  is a separate plastics moulding attached to the rear surface of chamber  17 . Water in ducting  36  is directed back into tie bottom of chamber  17  through an aperture (not shown) in the chamber wall located in registration with the sump portion  33  of duct  36 . 
     In order to inflate gasket  18 , an air pump is provided which is preferably a solenoid driven diaphragm pump. This pump is mounted inside the rear wall of chamber  3  and couples to air hose  41 . The diaphragm pump is energised using a chopped DC supply provided by the dishwasher controller. 
     In use, when chamber  201  is loaded with dishes and fully retracted within cabinet  203  and the dishwasher powered on, the air pump is activated to inflate gasket  18  to cause lid  217  to seal off the top of chamber  201 . The end of the inflation cycle is indicated by the attainment of a desired pressure in gasket  18 . The dishwasher controller then initiates the wash cycle. The chamber remains sealed until the drying cycle terminates or until the user withdraws chamber  201  from cabinet  203 . During this period the air pump maybe cycled on from time to time to ensure adequate sealing pressure is maintained in gasket  18 . 
     A further embodiment is shown in FIG. 14 where lid  217  and the rim  19  of wash chamber  201  are provided with complementary inclined edges along the sides thereof. A resilient sealing member is disposed about the periphery of lid  17 . When wash chamber  201  is fully retracted in cabinet  203  it seals against lid  17  by virtue of the wedging action that results as a result of the fore-aft inclinations of the lid and chamber rim. 
     In a further alternative configuration (not shown) a flat rigid lid is provided with a peripheral flexible gasket which cooperates wit means on the wash chamber rim so that positive sealing between the lid and wash chamber is achieved by a pure sliding action when the chamber is retracted into the cabinet. 
     FIGS. 15 to  17  show alternative embodiments where instead of the use of a rigid lid, a flexible closure is used. In FIG. 15 a curtain type closure  24  is fixed along edge  25  to the rear segment  26  of wash chamber rim  19 . Curtain  24  is retractably stored on a spring-loaded roller  27  mounted in the top front of the dishwasher cabinet  203 . When wash chamber  201  is withdrawn, curtain  24  is taken up on roller  25  whereas when the wash chamber is retracted, curtain  24  is played off roller  25  to fully cover the open top of the wash chamber  201 . 
     FIG. 16 shows a flexible closure  27  provided with a concertina type configuration and mounted in slides provided in the top sides of the dishwasher cabinet When the wash chamber  201  is withdrawn from cabinet  203  as shown in FIG. 17, closure  27  folds up due to concertina action where when the wash chamber is retracted as shown in FIG. 16 a closure  27  is opened out so as to lie flat along the top of the wash chamber. 
     A further embodiment is shown in FIG. 18 and 19. In this embodiment lid  217  is fitted with an inflatable annular member about its outer edge and this member is inflated as shown in FIG. 19 to sealably engage against the side of the interior wall of wash chamber  201 . In this case the rear wall of the wash chamber is reduced in height to allow the wash chamber to slide into the cabinet notwithstanding that the lid is fixed in a vertical position lower than the top edge of the chamber walls. 
     In addition to using a moving or expanding sealing member onto the top of the wash chamber when it is retracted into the cabinet a separate seal support carrier may be interposed between the periphery of the lid and the sealing member with close being achieved by lowering the support carrier. This is shown in FIG. 39, where a seal support carrier  252  is attached to lid  217  by an expandable skirt  253 . A variety of actuator means giving reciprocal motion can be used to move the seal carrier. 
     An alternative flexible closure arrangement is shown FIG.  42 . An endless belt  260  mounted on rollers  261  having a width equally to the width of the wash chamber and spacing between rollers approximately equal to the length of the wash chamber covers the top of the chamber when it is fully retracted. 
     The rollers  261  are mounted at a fixed height in the top of he washer cabinet. The top edge of the rear wall  262  of the chamber is fixed to the belt  260  so that it is rotated and given the same linear motion as the chamber as it is slid closed. A pressure pad  263  may be used to ensure sealing of the belt against the wash chamber and the belt may be stiffened by a series of spaced apart transverse battens. 
     In the embodiments so far described the closure  217  is essentially fixed in the vertical direction within cabinet  203 , whether rigid or flexible. In the following embodiments the closure is moved downwards by various means to sealably close the open top of wash chamber  201 . 
     A first such embodiment is shown in FIGS. 20 and 21. Here a peripheral resilient sealing member  20  is disposed on the underside of lid  217  while an inflatable annular member  21  is used to force lid  217  downward in a vertical direction to seal against rim  19  of the wash chamber as shown in FIG.  19 . 
     A further embodiment is shown in FIGS. 22 and 23. Here lid  217  is mounted in the top of cabinet  203  so as to be movable in a vertical direction from the position shown in FIG. 22 to the position shown in FIG.  23 . Sealing is achieved by providing flange configurations around the edge of the lid and in the top of the wash chamber wall so that when closed, as shown in FIG. 23, an impassable labyrinthic fluid path  22  is formed to thereby effectively seal the wash chamber. The lid and wash chamber flange configuration form a pressure equalisation chamber which ensures wash liquid does not escape. This configuration of lid can also be used in a fixed lid mode if the rear wall of the wash chamber is of reduced height to provide clearance for the lid flanges as it is slid into the closed position. 
     In addition to the labyrinthic path configuration sealing may be assisted by flexible deformable sliding members  264  shown in FIG.  43  and/or by a linear brush member  265  shown in FIG.  44 . 
     An alternative means of raising and lowering a rigid lid is shown in FIG.  40 . Compression springs  253  apply a lifting force to lid  217  and maintain it in a normally open position. Tension springs  254  are used to apply a closing force to the lid when the wash chamber is fully retracted into cabinet  201 . Tension is applied by a roller  255  attached to one end of the spring travelling over cam or ramp  256  prior to fill retraction of the wash chamber. A latch  257  maintains tension in the spring after the roller has passed over cam  256 . This is released when it is later desired to raise the lid. A second latch  258  takes the downward force due to the extended spring  254  until the wash chamber is fully retracted whereupon it releases member  259  to allow a closing (lowering force) to be applied to lid  217 . 
     Another mechanism for raising and lowering a rigid lid is shown in FIGS. 45 to  47 . A cam and cam follower arrangement is used as follows. Lid  217  is mounted in the top of cabinet  203  on compression spews  270  although restricted against horizontal movement Wash chamber  201  is provided with cam surfaces  266  and  267  on the outside of each side wall which engage corresponding rollers  268  and  269  as the chamber is moved horizontally to the retracted position. Surface  266  first contacts roller  268  and causes the front of lid  217  to lid as shown in FIG.  46 . Similarly surface  267  contacts roller  269  and lifts the rear end of lid  217  all the wash chamber is ret ed further. At the end of horizontal travel (FIG. 47) the rollers move down into the semicircular portions of cam surfaces  266  and  267  under the influence of springs  270  to lower the lid  217  onto the top of the wash chamber and close it. 
     This cam and cam follower technique can be used with the wedged configuration of lid and wash chamber walls which was shown it FIG.  14 . This can assist in achieving an increased sealing force by providing a vertical force component in addition to the horizontal component caused by pushing the wash chamber into the cabinet. A cam and cam follower arrangement can also be used to raise and lower the rear end of the lid in constructions where the front of the lid is pivoted about a transverse horizontal axle at a fixed height in the upper front of the cabinet. 
     Water Management System 
     In a dishwasher of the double wash tub configuration shown in FIG. 7 water may be transferred between the upper and lower tubs  202   a  and  202   b  to minimise the total volume of water consumed in the wash cycles. 
     Referring to FIG. 24, cabinet  203  contains an upper wash tub  202   a  and a lower wash tub  202   b . Each tub has a drain pump  135  fed by a soil pipe  57  from drain sump  136 . The soil pipe on wash tub  202   a  has a branch pipe  137  connected to a valve  138  with the configuration being such that when valve  138  is open water from upper tub  202   a  can flow through branch pipe  137  into lower wash tub  212   b.    
     A typical wash programme for each wash tub will be; pre-rinse, wash, post-rinse  1 , post-rinse  2 . 
     According to this aspect of the invention water used in the upper tub post-rinse cycle  1  is provided to the lower wash tub for its pre-rinse cycle and the water used for the upper tub post-rinse cycle  2  is provided to the lower wash tub for its wash cycle. Thus the dishwasher controller is programmed to implement this sequence of events by staggering the wash cycles for wash tub  202   a  and wash tub  202   b  so that the wash programme for tub  202   b  is not commenced until the end of post-rinse cycle  1  for the upper tub  202   a . At that point, valve  138  is opened to allow the rinse water from tub  202   a  to flow into tub  202   b . The wash programme for tub  202   b  then commences with a pre-rinse cycle using the water from tab  202   a . If the post-rinse cycle  2  time period is the same as the pre-rinse cycle time period, then at the conclusion of post-rinse cycle  2  for tub  202   a , the rinse water is discharged into tub  202   b  at the commencement of the wash cycle for that tub. 
     Other wash programmes may be constructed using the above concepts to similarly conserve a greater or lesser degree of wash water. 
     Drain Pump 
     Referring to FIG. 25 the present washer (as was the case WO 93/12706) uses a single motor to drive both the wash pump and drain pump impellers which are mounted at opposite ends of the motor rotor shaft. As in WO 93112706 the rotor rotates within a well in the washer floor while the motor stator is mounted external to the well under the sliding wash chamber. The wash pump is active when the motor rotates in one direction while the drain pump is active when the motor rotates in the opposite direction. 
     In FIG. 25 motor rotor  105  is mounted coaxially within well  106  provided in removable central floor section  51  of the wash chamber. Rotor  105  is splined onto a drive shaft  52  which extends out of opposite faces of the rotor. The upper portion of drive shaft  52  carries a wash pump impeller  95  (pump casing and spray system not shown), while the lower section of the drive shaft carries a drain pump impeller  54 . The lower portion  58  of well  106  provides a casing within which impeller  54  operates to pump wash water draining into sump  58  into waste pipe  57 . 
     It is necessary to prevent soiled wash water from entering the gap between well  106  and rotor  105  so as to reduce wear on the rotor and to eliminate the possibility of jamming the rotor. In the present invention, a plastics sealing ring  59  is mounted on shaft  52  between the lower face of rotor  105  and the upper face of impeller  54 . However without further measures, seal  59  causes air induced into the drain pump to build up to such an extent that liquid priming of the pump may be impeded or prevented 
     This problem is overcome in the present invention by ensuring soil pipe  57  leaves the drain pump sump at an inclination of around  6  from the horizontal and by appropriately shaping vanes  55  of the pump impeller. When soil pipe  57  is upwardly inclined, air accumulated up against seal  59  can be bled off so that it does not extend below the level of point  60 . 
     Referring also to FIG. 26 the vanes  55  of impeller  54  are provided with a vertical slot  61  at their roots to provide an annular gap in which trapped air may accumulate when the impeller commences rotating. This allows adequate priming to achieve proper operation of the drain pump. 
     Heating Element Protection 
     A heating element for the present dishwasher takes the form of an annular plate which comprises part of the floor of the dishwasher as in WO 93/12706. The heating element shown in FIGS. 27 and 28 consists of a thick film circuit  120  printed on a substrate comprising a steel (or alloy of steel) plate  121  covered with a porcelain enamel coating  122 . The enamel forms the dielectric and consists of a ground coat and a cover coat, each of which is separately fired The thick film resistive circuit  120  consists of a palladium silver composition which is in turn fired on to the enamel coating. Alternatively polymer materials may be coated on the steel plate to form the dielectric. These can be cured and do not need to be fired in a high temperature furnace as is the case with enamel. 
     If the element runs dry, temperature build up will be such that the thick film track burns and open circuits to cause energy dissipation in the heater element to cease and thereby minimise excessively high temperature build up in the wash tub which may damage plastic supporting components. However, this inherent protection is insufficient to meet some electrical standards and accordingly a sensor circuit which disconnects power from the element is provided. As the steel plate  121  is earthed in use, over temperature in the element system is detected in the present invention by monitoring the leakage current to earth. It will be appreciated that as the enamel dielectric undergoes a local increase in temperature, some current will flow between the thick film  120  and the steel substrate  121 . 
     An earth leakage protection circuit suitable for providing protection for the element system is shown in FIG. 29, Element  120  is energised from AC man supply (phase P, neutral N) through series switching devices comprising a triac  123  and a relay  124 . A differential current transformer  125  is coupled to the AC supply to element  120  and produces a voltage in winding  126  if an out of balance current exists in the supply phase and neutral conductors. This will occur if there is any leakage of the heater supply to the earthed element plate  121 . 
     An operational amplifier  127  monitors the voltage across transformer winding  126  and when the earth leakage current exceeds a predetermined maximum, say 20 mA, the output of operational amplifier  127  switches npn transistor  128  into saturation mode. This allows excess current to flow from the 12 volt DC rail supply  129  through 200 mA use  130 , pnp transistor  133 , relay coil  131  to earth. The fuse blows and removes the supply of current to the relay coil  131 , thus opening relay switch  124  to disconnect supply from element  120 . 
     The present invention also provides a failsafe circuit for the earth leakage triggering circuit described so far. This ensures that element  120  cannot be turned on in the event that the circuit described develops a fault. 
     Accordingly a resistor  132  supplies a small AC “bias” current (which may be around 5 mA) through current transformer  125 . This produces a small out of balance voltage across winding  126  which produces a positive voltage offset at the output of operational amplifier  127  which in turn causes enough current to flow through transistor  128  to bias on resistor  133 , thereby allowing enough current to flow through relay winding  131  and hold relay switch  124  on. The current in transformer winding  126  is insufficient to cause enough current to flow through fuse  130  and transistor  128  to cause the fuse to blow. With this arrangement, if any part of the protection circuit fails, the current flow through resistor  132  ceases, the ‘bias’ offset in winding is no longer detected and transistor  133  is turned off to de-energise the relay causing switch  124  to open and remain open while this state exists. 
     Detergent Dispenser 
     A detergent dispenser for use in the present dishwasher is illustrated in FIGS. 30 to  37 . The detergent dispenser fits behind the interior front wall  4  of the wash chamber and is accommodated within the thickness of front panel  202  (see FIG.  1 ). 
     Referring to FIGS. 30 to  32 , the detergent dispenser is formed by providing a moulded receptacle  5  within a substantially rectangular aperture  6  within wash chamber wall  4 . A pivoted or hinged door  8 , which closes off receptacle  5 , provides a sub-frame to which detergent containers  9  and  10  are mounted. A vent  11  provides a communication between receptacle  5  and the wash chamber even when door  8  is closed Vent  11  allows detergent to enter the wash chamber in a manner described below. Two water outlet nozzles  12 A and  12 B (only one nozzle is shown in FIGS. 30 and 31) are positioned in the top of receptacle  5  and located so a to discharge water into detergent containers  9  and  10  respectively. 
     Operation of the detergent dispenser is as follows, Detergent is loaded into the detergent containers  9  and  10  as shown in FIG.  30 . Door  8  is opened for this purpose. It is then closed and wash chamber  1 , loaded with dishes, is retracted into cabinet  3 . At the appropriate time in the wash cycle the dishwasher controller opens a valve to allow water to discharge from nozzle  12 B. This nozzle discharges into the smaller detergent container  10  in a rinse cycle prior to the main wash cycle. However the action of the detergent dispenser will be explained with reference to nozzle  12 A discharging into larger container  9 . The discharge causes water to mix with the detergent in container  9  and flush the water/detergent mixture out of the top of the container  9  to spill into receptacle  5 . The detergent containers are provided with a small bottom aperture  13  (as shown in FIG. 33) for drainage. The aperture is sufficiently small to prevent discharge of dry detergent. The water/detergent mix then enters the wash chamber through vent  11 . 
     Receptacle  5  may be mounted in wash chamber wall  4  using clamps tightened by screws which serve to compress an O-ring to seal the dispenser flange to wall  4  of the wash chamber in a known way. The provision of water outlets in the moving wash system means that a water supply hose  229  must flexibly extend between the cabinet and the wash chamber into front panel  202 . This is arranged together with a dram hose and electrical wiring to form a hose wiring bundle  228  as shown in FIG.  3 . 
     The present dishwasher dispenser does not impinge on wash chamber volume, does not rely on wash water to dispense detergent and has no moving parts that may be fouled during the dispensing cycle. While described for use in a dishwasher of the sliding drawer type, it may be used in dishwashers of conventional design having a front opening door to the wash chamber. 
     In the preferred form the detergent dispenser is moulded from plastics in two parts, namely receptacle  5  and door  8  as shown in FIGS. 35 and 36. To reduce components the water conduits and valve casings are integrally moulded in receptacle  5 . This can be seen in FIG.  36 . As previously mentioned, water must be controllably released in the detergent dispenser through either of nozzles  12 A or  12 B. A two-way shuttle valve  151  is used to divert water entering the dispenser water inlet  152  between a respective outlet  153  or  154 . Outlet  154  discharges into the pre-rinse detergent container while outlet  153  delivers water into the main wash detergent container. The water paths and the valve casing are all provided within the detergent dispenser moulding. 
     Two-way valve  151  which is shown in more detail in FIG. 37, comprises a seal  155  reciprocated between one of two positions by a solenoid armature  156  within a solenoid coil (not shown). 
     The dishwasher controller at appropriate points in the wash cycle opens a valve to supply water to detergent dispenser inlet  152 . This water flows through passageway  157  to port  158  of the two-way valve  151 . If valve seal  155  is in the position shown, water entering port  158  is able to exit bough port  159  from whence it proceeds through passageway  160  which discharges through outlet  153 . The water so discharged then enters detergent container to function as previously described. 
     If solenoid armature  156  is retracted, valve seal  155  abuts against valve seat  161  prevent water entering inlet port  158  from exiting through outlet port  159 . However, the water entering the valve body may exit through outlet port  162 . It then enters into water passageway  163  to be subsequently discharged at outlet  154 . This is the discharge point for the flushing of pre-rinse detergent container  10 . 
     The detergent dispenser moulding also incorporates a rinse aid reservoir  164  and the Be aid liquid is dispensed into the wash chamber in a metered volume by a pump  165 . This pump is preferably a solenoid operated diaphragm pump which is supplied with pulsed DC and the volume of rinse aid dispensed is directly proportional to the period for which pump  165  is activated. 
     A charge of rinse aid is admitted into the wash chamber during the main wash cycle as follows. A solenoid driven diaphragm pump connected can its section side to a refillable rinse aid reservoir is energised with chopped direct current for a predetermined time. The time is pre-stored in the dishwasher controller and is set to deliver an optimum volume of rinse aid for normal washes.