GB2139084A

GB2139084A - Waste heat utilisation in the operation of a dishwashing machine

Info

Publication number: GB2139084A
Application number: GB08408152A
Authority: GB
Inventors: Ernst Stickel; Helmut Jerg
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-05-06
Filing date: 1984-03-29
Publication date: 1984-11-07
Also published as: GB8408152D0; IT8420787A1; FR2545347B1; IT8420787A0; IT1174069B; FR2545347A1; DE3316685A1; GB2139084B; DE3316685C2

Abstract

To further reduce energy and water consumption in a household dishwashing machine as well as to shorten the running time of the rinsing programs and to meter more accurately the quantities of rinsing liquid to be added to the rinsing container in the program sections, a water reserve container (2), which is thermally conductively connected with a rinsing container (1) of the machine, is filled with cold water on each occasion after reaching the cleaning temperature or after the clear rinse and is emptied each time through delivery of certain quantities for preliminary rinse and cleaning or for intermediate rinse and clear rinse. The filling of the reserve container (2) always takes place through a storage container (5). Emptying of the reserve container takes place by way of ducts (11, 12) and ion exchange container (4) into the rinsing container (1). <IMAGE>

Description

SPECIFICATION Waste heat utilisation in the operation of a dishwashing machine The present invention relates to a method of operating a dishwashing machine, especially so as to utilise waste heat, and to a dishwashing machine for carrying out such method.

In a method known from DE-OS 2730489 for operation of a dishwashing machine, in a preliminary rinse program portion water from a freshwater feed duct or from a water reserve container is fed to a rinsing container, circulated through spray equipment and thereafter pumped away. In a cleaning program section, water from the freshwater duct or from the reserve container is fed to the rinsing container, heated up to a predetermined cleaning temperature by a heater and circulated. After a certain time, the reserve container is filled with water, which is preheated through thermal contact with the rinsing container as well as through a circulating duct conducted through the reserve container to an upper part of the spray equipment, the heater being switched off, and the spent rinsing liquid of the rinsing container is pumped away after the heat exchange.With the start of an intermediate rinse program section, the preheated water is let out of the reserve container into the rinsing container, and at the end of the clear rinse program section and after the emptying of the clear rinse liquid out of the rinsing container, the reserve container is filled up again with water for cooling of the rinsing container and for precipitation of water vapour forming in the drying program section. The water disposed in the reserve container is stored for the preliminary rinse or cleaning program section of a new program.

In this method, heat energy is withdrawn from the spent heated rinsing liquid and the fresh water used in subsequent program steps is heated up so that, apart from an appreciable energy saving, a careful treatment of crockery with respect to temperature fluctuations is achieved. Since the reserve container, designed for a rinsing container filling quantity of one rinsing operation, is emptied after the preliminary rinse, the rinsing container filling for the cleaning phase consists of fresh water and must be heated up from the fresh water temperature to the cleaning temperature. The reserve container is also emptied for the intermediate rinse so that filling of the rinsing container with cold or soft water takes place for the clear rinse and then has to be heated up to the clear rinse temperature.

In DE-GM 80 19951 there is disclosed a dishwashing machine which, in place of a balancing weight, has a water reserve container consisting of a blow-moulded synthetic material part which is filled with water only at the place of installation of the machine. This water container is arranged between the ion exchanger and the soft water inlet opening of the rinsing container, so that it is disposed in the pressure-free region of the water inlet into the rinsing container and can be constucted to be thin-wailed. Moreover, the water container is always kept filled. Through a cooling coil arranged at the rinsing container shell and connected with the water container, it is possible in the drying program section to convey the water stored in the water container through the cooling coil for the cooling of the rinsing container shell.

For more exact metering and matching of the quantity of regenerating agent to local water hardness, a storage container with at least two chambers and a ventilation valve is disclosd in DE-PS 31 44 866, which storage container is fillable during inflow of fresh water and the storage volume of which can flow out entirely or partially through an outflow duct into a salt reserve container for the introduction of a corresponding quantity of brine into an ion exchange container.

Moreover, for the determination of the quantity of water to be filled into the rinsing container, a level regulating device is known from DE-GM 82 18 877, which device has a first chamber of small volume flow-connected with the rinsing container of the machine by way of an overflow edge at the height of a certain filling level of the rinsing container, whilst a second chamber, arranged by way of the overflow edge in front of the first chamber, is connected with a water feed and the suction space of a discharge pump. The housing forming the chamber has an aeration opening and a switching device for blocking water feed into the rinsing container is connected to the first chamber. Both chambers are flowconnected through a siphon guided over the overflow edge.A float can be provided in the first chamber and a switch, actuable by the float to switch off the freshwater inlet valve, can be provided at the housing.

Finally, a safety valve detecting the safety level of the rinsing container as well as leakage water issuing from the machine is disclosed in DE-PS 3114 664.

In relation to the known machines and methods of operation thereof it would be desirable to reduce energy and water consumption even further and to make possible shortening of the running time of the rinsing programs as well as an accurate metering of the rinsing container filling quantities.

According to a first aspect of the present invention there is provided a method of operating a dishwashing machine comprising a rinsing chamber, spray means for spraying water into the rinsing chamber, a water reservoir thermally conductively connected to the rinsing chamber, a water storage chamber, and water softening means comprising a salt chamber and an ion exchange chamber, the method comprising the steps of carrying out a flushing operation by feeding part of a quantity of water stored in the reservoir through the ion exchange chamber and into the rinsing chamber, discharging the water from the rinsing chamber and refilling the reservoir with water, carrying out a preliminary rinsing operation by feeding into the rinsing chamber a part of the water stored in the reservoir, circulating the fed water through the spray means and discharging the circulated water from the rinsing chamber, carrying out a cleaning operation by feeding the rest of the stored water into the rinsing chamber, heating such water to a predeter mined temperature after or during addition thereto of an additive, circulating the heated water through the spray means, filling the reservoir and the storage chamber with water after attainment of said temperature and during said circulation so as to permit the water newly stored in the reservoir to be preheated by thermal conduction from the rinsing chamber, and discharging from the rinsing chamber the water therein after the preheating of said newly stored water, carrying out an intermediate rinsing operation byfeeding part of said preheated newly stored water into the rinsing chamber, circulating such water through the spray means, and discharging the circulated water from the chamber, carrying out a clear rinsing operation by feeding the rest of said newly stored water into the rinsing chamber, heating such fed water to a predetermined temperature, circulating the heated water through the spray means after or during addition of an additive, and discharging the circulated water from the rinsing chamber, carrying out a drying operation by refilling the reservoir with water so as to permit cooling of the rinsing chamber by thermal conduction from the reservoir, and carrying out an ion exchange operation during or afterthe drying operation by feeding water from the storage chamberto the salt chamber so as to displace brine into the ion exchange chamber.

In a preferred example of the method, in particular for the recovery of waste heat in a household dishwashing machine with a rinsing container, softening equipment comprising an ion exchange container and a salt reserve container, a discharge pump, a heaterforthe heating of rinsing liquid which is sprayable by means of a pump through a lower and an upper spray device onto the crockery, and a water reserve container which acts as a heat exchanger and is thermally conductively connected with the rinsing container, the method comprises the following steps:: a) in program steps, which are arranged before or after a preliminary rinse program section, a partial quantity of water is taken from the reserve container, conducted through the ion exchange container - for rinsing-through of the regenerated ion exchanger mass - into the rinsing container and pumped out of this and the reserve container is subsequently refilled; b) in the preliminary rinse program section, a part of the water stored in the reserve container is fed to the rinsing container, circulated through the spray devices and thereafter pumped away;; c) in a cleaning program section, the remaining water is fed out of the reserve container to the rinsing container, heated up, after or during the addition of an additive, to a predetermined cleaning temperature and circulated, and after attaining the cleaning temperature - with the heater switched off and the circulating pump still operating - the reserve container as well as a storage container arranged in the water feed duct upstream of the reserve container are filled with water, the filling of the reserve container being preheated through thermal contact with the rinsing container and the spent rinsing liquid of the rinsing container being pumped away after the heat exchange;; d) on the start of an intermediate rinse program section, a part of the preheated water is let out of the reserve container into the rinsing container, circulated through the spray devices and thereafter pumped away; e) in a clear rinse program section, the remaining water is fed out of the reserve container to the rinsing container, heated up to the predetermined clear rinse temperature, circulated after or during the addition of a clear rinsing agent, and thereafter pumped away; f) in a drying program section, the reserve container is filled with water for the cooling of the rinsing container and precipitation of the water vapour forming in the rinsing conainer and the water is stored for the preliminary rinse and cleaning program sections of a new program; and g) during or after the drying program section, water is conducted in one or more program steps out of the storage container into the salt reserve container and brine out of the salt reserve container into the ion exchange container.

Such a method exemplifying the invention is applicable in the normal program as well as in the economy-care programs or the economy-fine programs for sensitive crockery and in the intensive program for particularly dirty crockery. By means of this method, energy is withdrawn before pumping away of the spent rinsing liquid and is transferred to following rinsing operations so that the crockery experiences more careful treatment through the avoidance of large temperature fluctuations. The saved energy assists the heating-up operations and thereby contributes to reduction in the running time of the overall program.Due to the large temperature difference at the end of the clear rinse program section between the temperature of the hot crockery and the cold water flowing into the reserve container, the rinsing container surface lying against the reserve container forms a condensation surface which accelerates the drying of the crockery. The accurate metering of the quantity of water supplied to the rinsing container during each rinsing operation results from the arrangement of the reserve container, from which the desired partial quantities are always withdrawable independently of valve tolerances and of water duct pressure, while the reserve container can always be filled up again to an exactly determined volume. Since the reserve container is always filled during the loading and unloading of the machine, an additional balancing weight for the stability of the machine is not needed.

According to a second aspect of the present invention there is provided a dishwashing machine for carrying out the method of the first aspect of the invention, the machine comprising a rinsing chamber, spray means for spraying water into the rinsing chamber, a water reservoir thermally conductively connected to the rinsing chamber and provided with air vent means, a water storage chamber, water softening means disposed below the storage chamber and comprising a salt chamber and an ion exchange chamber, a water inlet duct including a water inlet valve and connected to an inlet of the storage chamber, a water feed duct communicating with the inlet duct by way of a free flow path within the storage chamber and connected to an inlet of the reservoir in an upper region thereof, metering and flow control means for conducting predetermined quantities of water from the reservoir to the ion exchange chamber, and an outflow duct connecting an outlet of the storage chamber to an inlet of the salt chamber.

In a preferred embodiment, the machine comprises a fresh water duct behind a fresh water inlet valve, the duct ending in a free flow path of a storage container which is disposed above softening equipment and from which on the one hand, behind the free flow path in direction of flow, a feed duct opens into a reservoir at the top and from which on the other hand an outflow duct connects with a salt reserve container of the equipment, the reservoir having an aeration duct and being connected to an ion exchange container of the equipment through metering and blocking means for the delivery of certain partial water quantities.

Since the volume of the reservoir suffices for the rinsing chamber fillings for two rinsing operations, a preliminary rinsing operation and a cleaning operation can be performed with the water stored from a preceding rinse program in the reservoir, in which case the rinsing liquor has to be heated up in the cleaning operation merely from the storage temperature to the desired cleaning temperature. Since the reservoir is empty during the heating sections, no heat energy is withdrawn from the rinsing chamber.

The water filling of the reservoir, which is heated up from the waste heat of the cleaning liquid before it is pumped away, again suffices for the intermediate rinse and clear rinse, in which case the clear rinse quantity of liquid has to be heated up in the clear rinse program section, with the reservoir emptied, merely from the storage temperature to the clear rinse temperature.

For program variants with, for example, several preliminary or intermediate rinsing operations or a cleaning operation with greater rinsing container filling quantity, the reservoir can after the withdrawal of the additionally required partial water quantities be filled up again in between. In analogous manner, the partial water quantity required for the rinsing-through of the regenerated ion exchange mass can be withdrawn from the reservoir, for example before the preliminary rinse, and this can thereafter again be filled fully before the partial water quantity for the preliminary rinse is withdrawn from the reservoir.

The process run-down is simple to control. The provision of rinsing chamberfilling quantities inde pendentofvalve results in accurate liquor quantities guaranteeing a good rinsing result. A water heater of the machine is loaded less, whilst an additional air heating can be dispensed with because of the cooling of the rinsing chamber during the drying. A condensation surface at the rinsing chamber wall generates an air current which promotes drying of the crockery, so that an additional blower can also be dispensed with.With the omission of an air heater, an overheat protection for the heater is also redundant, which heater can, for example, be restricted to a throughflow heater which can be so arranged that a heater no longer needs to be present in the rinsing chamber and openings in the rinsing chamber wall, heating rod holders, heating rod seals and thermostat seals are not needed.

Examples of the method and embodiments of the dishwashing machine of the present invention will now be more particularly described with reference to the accompanying drawings, in which: Figure 1 is a functional diagram of a first household dishwashing machine embodying the invention; Figure 2 is a schematic elevation of the dishwashing machine of Figure 1; Figure3 is a program diagram for the dishwashing machine of Figures 1 and 2; Figure 4 is a schematic elevation of a second household dishwashing machine embodying the invention; and Figure 5 is a schematic elevation of a third household dishwashing machine embodying the invention.

Referring now to the drawings, there is shown a household dishwashing machine comprising a rinsing container 1, which consists of thin-walled sheet metal and the rear wall of which is, in the illustrated embodiments, constructed to be double-walled to form a reserve container 2. Disposed above softening equiment consisting of a salt reserve container 3 and an ion exchange container 4 is a storage container 5, which is preferably arranged at a side wall of the rinsing container and from the base of which an outlet duct 6 leads into the salt reserve container. The machine is connected through a fresh water inlet valve fl to a water duct 7. A fresh water duct 8 of the machine leads from the inlet valve fl into the storage container 5 and communicates, by a nozzle-like end, with a free flow path 9 in the container 5.Behind the free flow path in the direction of flow, a feed duct 10 leads into the upper part of the reserve container 2.

The reserve container 2, which is fillable up to the height of the opening of the feed duct 10, is connected at its base by an emptying duct 11 and a controllable blocking valve f2 with the ion exchange container 4. In addition, in the embodiments of Figures 1 to 4, the container 2 is connected, in the region of a level threshold 10 between an upper volume V3 for preliminary rinse or intermediate rinse and a lower volume V4 for cleaning or clear rinse, by a second emptying duct 12 and a further blocking valve f3 with the ion exchange container, which is connected by a discharge duct with the rinsing container 1.

The salt reserve container 3, which for the regeneration of the ion exchanger mass stands in connection with the ion exchange container, for the replenishment of salt has a closable filling stub pipe 14 projecting into the rinsing container, and a regenerating valve f4 is also provided in the outlet duct 6.

For better matching of the quantity of brine, which according to local water hardness is needed on each occasion for the regeneration of the exhausted ion exchanger mass, the storage container 5 has two chambers V1 and V2 and a ventilatable valve 15. The two chambers V1 and V2, which are disposed beside each other, of the storage container 5 are separated by a wall 16 which is surmounted by a siphon 17, both limbs of which reach nearly to the base of both chambers. The elbow of the siphon 17 lies below the level 19 formed by an overflow duct 18, opening into the rinsing container, of the storage container 5.

Connected to the elbow of the siphon 17 is an aeration duct 20, which has the aeration valve 15 at its end.

During the feed of fresh water through the ducts 8 and 10 into the reserve container, the leakage water arising in the free flow path 9 is collected in the chambers V1 and V2 of the storage container 5. If the reserve container 2 is filled to the point that its water level reaches the opening of the feed duct 10, then due to the build-up arising in the duct 10, the storage container is filled with water in a short time to such an extent that its switching level 21 is reached, at which point the water flows over a partition 22 into an overflow chamber 23 and raises a float 24 disposed therein. The float actuates a switch 25, which closes the inlet valve fl and interrupts the water feed to the machine.The excess water, which is disposed between the filling level 19 of the chambers V1 and V2 and the switching level 21 in the storage container can flow through the overflow duct 18 into the rinsing container. A further siphon 26 serves for the emptying of the overflow chamber 23.

in dishwashing machines operated in areas of low water hardness, a small quantity of brine suffices for the regeneration of the filling of the ion exchange container. In the case of extreme water hardnesses, however, it is necessary to introduce a greater quantity of brine into the ion exchange container.

For the initiation of the regeneration process, during which no further water flows to the storage container 5, the stored water is freed by the regenerating valve f4 to flow through the outlet duct 6 to the salt reserve container 3. in that case, the chamber V1 empties initially as well as the water volume disposed above the wall 16 up to the level 19. In areas of smaller water hardness, the aeration duct 20 or its valve 15 is opened so that the siphon 17 is ventilated and thus ineffective. The water present in the chamber V2 therefore remains in the storage-container 5. The water flowing through the outlet duct 6 expels brine from the salt reserve container, which brine flows into the ion exchange container and effects regeneration of the ion exchanger mass.

In areas of greater water hardness, the aeration duct 20 or its ventilating valve 15 is closed so that the siphon 17 can become effective during the emptying of the storage container 5. During initiation of the regeneration process, an emptying therefore takes place of the chamber V1 as well as the chamber V2 of the storage container 5. The water stored in both the chambers V1 and 2 expels a larger quantity of brine out of the salt reserve container.

For the performance of a rinse program consisting of the program sections of preliminary rinse, cleaning, intermediate rinse, clear rinse, drying and regenerating, the following program course results according to Figure 3: For the rinsing-through D of the ion exchanger mass regenerated at the end of the preceding rinsing program, the blocking valve f2 is opened for a certain time over a step of the programme control device at the beginning of a new rinsing program and a quantity of water is conducted from the reserve container 2 through the ion exchange container 4 into the rinsing container 1 and pumped out of this through a switched-on discharge pump P.In the following program step, the reserve container 2 is again filled through opening of the inlet valve fl until the level transmitter 22 - 25 associated with the reserve container responds to the filling state of the reserve container and closes the inlet valve fl. For aeration of the reserve container, an aeration duct 27 extends above the feed duct 10 from the reserve container to the storage container 5.

The actual rinsing program now begins with a filling program step, in which the upper volume V3, intended for the preliminary rinse, can flow, with the valve f3 open, out of the reserve container by way of the ion exchange container and into the rinsing container. The water stored in the reserve container from the preceding rinsing program has, for example, a temperature of 20 C corresponding to the room temperature. After inflow of the accurately metered volume V3, the valve f3 is closed and, in the preliminary rinse phase, the rinsing container filling is circulated by means of a circulating pump U through spray equipment of the machine for the rinsing of crockery and thereafter pumped away by means of the discharge pump into a discharge system.

After completion of the preliminary rinse program section, the exactly defined, lower volume V4 is conducted in a further filling program step, with the valve f2 opened, out of the reserve container through the duct 11 and through the ion exchange container to the rinsing container. The reserve container is thereafter emptied completely, in which case the lower volume V4 conducted out of the reserve container to the rinsing container corresponds to the rinsing container filling needed for cleaning. The cleaning water is heated up, with the reserve container empty, to a temperature of, for example, 680C and in that case is circulated with the addition of a cleaning agent.After reaching the cleaning temperature and with the heater switched off, the reserve container is filled up through the opened inlet valve ~1, the duct 8, the free flow path 9 and the feed duct 10 until the level transmitter 22 - 25 closes the inlet valve fi. Through the circulating pump continuing to run, a heat exchange takes place between the cleaning fluid and the water of the reserve container. In that case, heat is withdrawn from the cleaning liquid and the water of the reserve container is heated up to, for example, 40 C. Since the cleaning liquor, thereupon to be conducted out into the discharge system, was also cooled down to this temperature, the outlet pipes and the environment are not loaded by hot cleaning liquor. Accordingly, an additional cold water feed for the coolingdown of the liquor can be dispensed with.

At the start of the intermediate rinse, the upper volume V3 of the preheated water is again discharged from the reserve container by way of the duct 12, the open valve f3 and the ion exchange container into the rinsing container. Since the temperature transition from cleaning to intermediate rinse is relatively small by reason of the heat exchange, the crockery is not exposed to undue temperature change. In the intermediate rinse phase, the rinsing container filling is circulated and thereafter pumped away.

After completion of the intermediate rinse, the reserve container is emptied completely through the duct 11 and the opened valve f2 into the rinsing container, in which case the volume V4, which is fed as soft water to the rinsing container, again corresponds to the quantity of water needed for the clear rinse. The water, already at 400C, is heated, with the addition of a clear rinse agent and with the reserve container empty, up to a temperature of, for example, 680C and is circulated through the rinsing device.

After the clear rinse liquid has been pumped out, the drying phase follows.

At the start of the drying phase, the reserve container 2 is filled with cold fresh water while the blocking valves f2 and f3 are closed and the inlet valve fl is opened, in which case the level transmitter 22 - 25 in turn effects the closing of the inlet valve.

Due to the cold fresh water, the wall between the rinsing container and the reserve container forms an effective condensation surface, on which the moist air present in the rinsing container precipitates.

Thereby, the drying process is accelerated without additional operation of a drying heater, and an air current forming in the rinsing container also has an additional advantageous effect. It is in that case also possible to insulate the rinsing container and the outside surface, remote from the rinsing container, of the reserve container without the function of the condensation surface being restricted or the drying process being significantly impaired. Apart from an effective heat insulation, a good noise insulation is possible at the same time.

During the drying phase, the regeneration of the exhausted ion exchanger mass can take place. Since the chambers V1 and V2 of the storage container 5 were also filled during the filling of the reserve container 2, the valve f4 can be opened with the valves f1, f2 and f3 closed so that, according to the setting of the aeration valve 15, water flows out of the chamber V1 or out of both the chambers V1 and V2 through the outlet duct 6 into the salt reserve container 3. In that case, a corresponding quantity of brine is forced into the ion exchange container 4. In the program run-down according to Figure 3, the introduction of the brine into the ion exchange container is divided up into two program steps separated in time. The control device motor is switched off after run-down of the last drying program step T.

The dishwashing machine is also equipped with a safety valve 28, which responds to the safety level in the rinsing container as well as to leakage water issuing from the machine. The safety valve for this purpose includes a pressure element which is connected through a pressure duct 30 with a safety level transmitter 29. The safety level transmitter, consist ing of an overflow chamber 31, an overflow partition 32, an air trap chamber 33 and a siphon 34, can be placed on the ion exchange container 4 (Figure 2) or integrated in the storage container 5 (Figure 4). For the detection of leakage water, a float 36 acting against the pressure element, for example a diaphragm, of the safety valve 28 is provided in a bottom trough 35 of the machine.

In the embodiment of Figure 5, the reserve container 2 is emptied merely through the valve f2, the duct 11 and the ion exchange container 4 into the rinsing container 1. For the accurate dimensioning of the volumes V3 and V4 of the reserve container, a float 38 equipped with a permanent magnet is guided in a tube 37 communicating with the ducts 10 and 11 and reed switches 39, which react to magnetic attraction and cooperate with the magnet of the float 38, are disposed at the height of the level threshold 13 between the volumes V3 and V4 and in proximity of the base of the reserve container. When the float reaches the level threshold 13 or the level of the reserve container base, then it effects closing of the valve f2 by way of the reed switch.

If a rinsing program is to be enlarged through a second preliminary rinse phase, by a cleaning operation with greater quantity of rinsing liquid and/or by a second or third intermediate rinsing operation, then the additional quantities of water are also withdrawn from the reserve container, which is then refilled by way of the controllable inlet valve fl after each additional withdrawal of water.

Claims

1. A method of operating a dishwashing machine comprising a rinsing chamber, spray means for spraying water into the rinsing chamber, a water reservoir thermally conductively connected to the rinsing chamber, a water storage chamber, and water softening means comprising a salt chamber and an ion exchange chamber, the method comprising the steps of carrying out a flushing operation by feeding part of a quantity of water stored in the reservoir through the ion exchange chamber and into the rinsing chamber, discharging the water from the rinsing chamber and refilling the reservoir with water, carrying out a preliminary rinsing operation by feeding into the rinsing chamber a part of the water stored in the reservoir, circulating the fed water through the spray means and discharging the circulated water from the rinsing chamber, carrying out a cleaning oeration by feeding the rest of the stored water into the rinsing chamber, heating such water to a predetermined temperature after or during addition thereto of an additive, circulating the heated water through the spray means, filling the reservoir and the storage chamber with water after attainment of said temperature and during said circulation so as to permit the water newly stored in the reservoir to be preheated by thermal conduction from the rinsing chamber, and discharging from the rinsing chamber the water therein after the preheating of said newly stored water, carrying out an intermediate rinsing opertion by feeding part of said preheated newly stored water into the rinsing cham ber, circulating such water through the spray means, and discharging the circulated water from the chamber, carrying out a clear rinsing operation by feeding the rest of said newly stored water into the rinsing chamber, heating such fed water to a predetermined temperature, circulating the heated water through the spray means after or during addition of an additive, and discharging the circulated water from the rinsing chamber, carrying out a drying operation by refilling the reservoir with water so as to permit cooling of the rinsing chamber by thermal conduction from the reservoir, and carrying out an ion exchange operation during or after the drying operation by feeding water from the storage chamber to the salt chamber so as to displace brine into the ion exchange chamber.

2. A method as claimed in claim 1, comprising carrying out a further preliminary rinsing operation following performance of the first-mentioned preliminary rinsing operation, the reservoir being replenished after withdrawal of water therefrom in the further preliminary rinsing operation and before performance of the next following operation.

3. A method as claimed in either claim 1 or claim 2, comprising carrying out at least one further intermediate rinsing operation following performance of the first-mentioned intermediate rinsing operation, the reservoir being replenished after withdrawal of water therefrom in the or each further intermediate rinsing operation and before performance of the next following operation.

4. A method as claimed in any one of claims 1 to 3, wherein the reservoir is replenished to enable the cleaning operation to be carried out with an increased quantity of water.

5. A method as claimed in any one of the preceding claims, wherein filling of the reservoir is carried out exclusively by way of the storage container and feeding of water from the reservoir to the rinsing chamber is carried out exclusively by way of the ion exchange chamber.

6. A method substantially as hereinbefore described with reference to the accompanying drawings.

7. A dishwashing machineforcarring out the method claimed in claim 1, the machine comprising a rinsing chamber, spray means for spraying water into the rinsing chamber, a water reservoir thermally conductively connected to the rinsing chamber and provided with air vent means, a water storage chamber, water softening means disposed below the storage chamber and comprising a salt chamber and an ion exchange chamber, a water inlet duct including a water inlet valve and connected to an inlet of the storage chamber, a water feed duct communicating with the inlet duct by way of a free flow path within the storage chamber and connected to an inlet of the reservoir in an upper region thereof, metering and flow control means for conducting predetermined quantities of water from the reservoir to the ion exchange chamber, and an outflow duct connecting an outlet of the storage chamber to an inlet of the salt chamber.

8. A dishwashing machine as claimed in claim 7, wherein the storage chamber is fillable by at least one of water from the free flow path and water overflowing, by way of the feed duct, from the reservoir when full and is provided with at least two compartments, means to cause water selectably from one or from both of the compartments to be delivered through the outflow duct to the salt chamber, means for controlling flowthrough the outflow duct and level sensing means so responsive to the level of water in the storage chamber as to cause the water inlet valve to be closed when the reservoir and the storage chamber are full.

9. A dishwashing machine as claimed in claim 8, the level sensing means comprising a further compartment disposed in the storage chamber and separated from said at least two compartments by an overflow partition, siphon means for emptying water from the further compartment, a float movable in the further compartment in dependence on the level of water therein, and switching means operable by the float in the uppermost position thereof to cause the inlet valve to be closed.

10. A dishwashing machine as claimed in any one of claims 7 to 9, the air vent means comprising an aeration duct connecting the reservoir to the storage chamber, and the storage chamber being connected by an overflow duct to the rinsing chamber.

11. A dishwashing machine as claimed in any one of claims 7 to 10, the metering and flow control means comprising an outlet duct connecting the base of the reservoir to the ion exchange chamber, a controllable valve arranged in the outlet duct, and means arranged in the region of the division between a predetermined upper and predetermined lower volume of the reservoir to permit discharge from the reservoir of a quantity of water equivalent to the upper volume.

12. A dishwashing machine as claimed in claim 11, said means arranged in the region of the division comprising a further outlet duct connected to the reservoir at said region, a further controllable valve being arranged in the further outlet duct.

13. A dishwashing machine as claimed in claim 12, said means arranged in the region of the division comprising a control device so responsive to the level of the water in the reservoir during emptying thereof by way of the outlet duct as to cause the controllable valve to be closed when the water level is disposed at said division.

14. A dishwashing machine as claimed in claim 13, wherein the control device comprises a magnetic float and a reed switch.

15. A dishwashing machine as claimed in claim 13, the control device comprising photoelectric means.

16. A dishwashing machine as claimed in either claim 8 or claim 9, the means for controlling flow through the outflow duct comprising a valve con trollabie in dependence on an operating programme of the machine, and a safety valve operable by safety level sensing means to control water flow through the water inlet duct.

17. A dishwashing machine as claimed in claim 16, the safety level sensing means comprising a water overflow chamber communicating with one of the storage chamber and the ion exchange chamber, siphon means for emptying water from the overflow chamber, an air trap chamber communicating with the overflow chamber, and a pressure duct connecting the air trap chamber to the safety valve, and the safety valve comprising a valve diaphragm responsive to air pressure in the pressure duct.

18. A dishwashing machine as claimed in claim 8, wherein the water inlet and feed ducts are so arranged as to continue filling of the storage chamber after the reservoir is full and until the level sensing means responds when the storage chamber is full.

19. A dishwashing machine as claimed in any one of claims 7 to 18, comprising heating means arranged in a water flow path from the spray means to the rinsing chamber.

20. A dishwashing machine substantially as hereinbefore described with reference to Figures 1 to 3 of the accompanying drawings.

21. A dishwashing machine substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.

22. A dishwashing machine substantially as hereinbefore described with reference to Figure 5 of the accompanying drawings.