Device for the liquid supply and dosage in a domestic washing machine tub, in particular a dishwashing machine

Abstract

 A device is described, for the liquid supply and dosage in the tub (7) of a domestic washing-machine tub, in particular a dishwasher, wherein the liquid dosage is realized by detecting the level of the liquid being present within the tub (7), said device (6) comprising detection means (16A,16B,17A,17B,18A,18B,19A,19B) located outside the tub (7) and operating on the basis of the amount of liquid supplied in the tub, a conduit (C2,13,T) being provided to put said detection means (16A,16B,17A,17B,18A,18B,19A,19B) in communication with said tub (7). According to the invention, closure means (V) are provided, for shutting said duct (C2,13,T) at the end of a liquid supply operation in the tub (7), so as to prevent the substantial liquid return from said tub (7) towards said detection means (16A,16B,17A,17B,18A,18B,19A, 19B).

Description

[0001] The present invention refers to a device for the liquid supply and dosage in the tub of a domestic washing machine, in particular a dishwasher.

[0002] It is known for dishwashers to comprise a washing tub, on whose bottom water from the mains is collected as required for the washing of the crockery; to this purpose, the machine has a washing or re-circulating pump to supply said water collected on the tub bottom to one or more spraying elements.

[0003] Water dosage as required for the washing can be performed in several ways.

[0004] The simplest solution is to provide a time-operated opening of a solenoid valve for water intake in the washing tub; however, such a method, practically given up by now, may prove poorly accurate as it does not consider the pressure changes that may always occur in the water supply mains and consequent changes in the flow-rate of the solenoid valve.

[0005] At present, the most spread solution, essentially due to saving reasons, is to realize the washing water dosage through an electro-pneumatic pressure switch, which through an air trap is apt to detect the water level directly inside the wash-tub, so as to ensure a control principle of the intake solenoid valve from the mains.

[0006] However, though being a cost-effective method, it requires a highly accurate calibration of the pressure switch (i.e. an expensive operation during the manufacturing stage); considering, in fact, that the washing tub has a rather extended section, even a few millimeters change of the water level in the tub may lead to a dosage error of several liters of water. Now, this is against the requirement of having machines whose consumption are strictly under control.

[0007] Moreover, the electromechanical pressure-switch, with time tend to loose its accuracy, with the result of a higher water intake than strictly required; on the other hand, re-calibration of the pressure switch on washing machines already installed represents such a critical operation to make its replacement a preferable solution; as a result, a water intake and dosage error is passively accepted in most instances.

[0008] Additionally, the fact that the air trap required for the pressure-switch operation is located practically inside the wash-tub, may determine a malfunction of the system, due to soil particles depositing right in the air trap.

[0009] Other solutions are also known, which are presently given up, wherein the water level is detected directly inside the wash-tub through a mushroom float, whose shaft is apt to cause switching of an electric contact; anyway, operation of this float is negatively influenced by the soil particles possibly present in the washing tub, which may even cause the float to become jammed up.

[0010] According to other known solutions, the water level to be reached inside the washing tub is predetermined through a proper height location of a siphon, so that as soon as a tiny amount of water exceeds the siphon bend, a detection device will immediately stop the electric supply of the solenoid valve.

[0011] However, also these supply and dosage devices have some drawbacks, since they are located inside the washing tub or adjacent to it; this may cause a malfunction due to heat development inside the tub, or soil particles depositing right inside the siphon or in correspondence with the detection device.

[0012] The shape of the floats employed in such solutions, i.e. either cylindrical or parallelepiped, may also lead to a lack of detection accuracy, as they are subject to frictions. Such floats, in fact, tend to adhere to or possibly become embedded in the walls of the relevant housing chamber, as well as collect soil particles.

[0013] Since a higher water intake than actually required is against the requirements of consumption reduction (water has also to be heated for washing purposes), in the instance of top-range washing machines the pressure-switch system is replaced by other solutions performing water dosage outside the washing tub.

[0014] Accordingly, solutions are known where the dishwashing machine comprises a metering tank branched off the water supply pipeline to the wash-tub, so that an amount of water from the mains will reach the tub directly and another portion said tank.

[0015] The metering tank has a reduced water capacity compared to the amount of water required for washing and contains a float level sensor, which therefore operates on a small amount of water, which is proportional to the amount supplied to the tub; upon reaching the predetermined level in the tank, it will cause the water intake solenoid-valve to close. In other words, the level sensor operates on a fraction of the water supplied to the tub, filling a small tank to minimize detection faults.

[0016] However, also this system is not free from detection faults, due to possible discrepancies in the flow-rate distribution in the by-pass pipe supplying the metering tank; additionally, this system also appears quite expensive compared to the previous ones.

[0017] Other water intake and dosage systems are also known, which provide a repeated water intake to one or more tanks, whose capacity equals a fraction of the capacity required for washing; also in this instance, at least one tank has a cylindrical or parallelepiped float level sensor, to control a standard intake solenoid-valve; water supply to the wash-tub occurs by subsequent transfers from the tank to the tub itself.

[0018] Such systems may require a long water supply time for washing and, anyway, their manufacture is complicated and expensive.

[0019] Moreover, the last two cited systems have a drawback inasmuch as high molding accuracy for the tank body is required, as seats should be provided on it for the fastening of the level sensors.

[0020] Substantially, dosage solutions as presently known and employed can be classified in two categories according to their detection system:

• systems with detection means operating on the whole liquid amount supplied to the tub, i.e. with dosage being performed by liquid level detection directly inside the wash-tub; such systems have the advantage of a low-cost manufacture, but a drawback from a standpoint of dosage accuracy and reliability;
• systems with detection means operating on a reduced amount of water required for washing, i.e. with the dosage being performed outside the washing tub; such systems have the advantage of a high dosage accuracy and reliability, but a drawback from a standpoint of manufacturing costs and operation times.

[0021] It is the object of the present invention to solve the drawbacks described above for said known devices.

[0022] Within this frame, it is a first aim of the present invention to provide a device for the liquid supply and dosage in the tub of a domestic washing machine, in particular a dishwasher, wherein the liquid dosage is obtained by detecting the liquid level inside the wash-tub, which is simple, compact and consequently of low-cost manufacture, and which allows for achieving a higher dosage accuracy, an improved reliability in use, an easier and cost effective manufacture, compared to other known solutions based on a similar operating philosophy.

[0023] A further aim of the present invention is to provide a device as described above, which has an improved reliability, by virtue of appropriate means to hinder the back-flow of soil residuals, possibly retained in the washing tub, to the liquid dosage means.

[0024] These and other aims are reached according to the present invention by a device for the liquid supply and dosage in the tub of a domestic washing machine, in particular a dishwasher, incorporating the features of the annexed claims, which form an integral part of the description herein.

[0025] Further aims, features and advantages of the present invention will become apparent from the following detailed description and annexed drawings, which are supplied by way of non limiting example, wherein:

• Fig. 1 shows schematically a portion of the hydraulic circuit of a washing machine, particularly a dishwasher, using a device for the liquid supply and dosage according to the features of the present invention;
• Fig. 2 shows schematically a section of a device according to the present invention, which is obtained according to a possible first embodiment, in a first operating condition;
• Fig. 3 shows schematically a front view of a first detail of the device represented in Fig. 2;
• Fig. 4 shows schematically a front view and a side view of a second detail of the device represented in Fig. 2;
• Fig. 5 shows schematically a section of a device as represented in Fig. 2, in a second operating condition.

[0026] Fig. 1 shows schematically a portion of the hydraulic circuit of a washing machine according to the features of the present invention; in the example represented in the figure the invention is applied on a dishwashing machine.

[0027] In this figure, reference 1 indicates a connection to the water mains (such as a tap) being connected to a conduit 2 for supplying the water from the mains to the dishwasher; on this conduit 2 a solenoid valve 3 controls the supply of the mains water to the dishwasher; on the conduit 2, downstream of the solenoid valve 3, a non-return device 4 generally known as air-breaker and a softening device 5 are arranged in series. It should be appreciated that the softening device 5 may not be absolutely required for a dishwasher, provided water hardness in the area where the latter is installed has a low degree.

[0028] Since devices 3, 4 and 5 pertain to known current manufacture and operation, they will not be further described in detail. However, it should be mentioned that the presence of an air-breaker usually entails introduction of a certain amount of air in the hydraulic circuit of a washing machine, which is conveyed to the wash tub. A certain amount of such air tends to accumulate in the conduit section closer to the tub, due to water filling in the latter.

[0029] Downstream of the softening device, always on the conduit 2, a dosage device 6 is provided for the washing liquid, manufactured according to the features of the present invention; a T-tube connects the device 6 to a washing tub 7 of the machine, which has a drain conduit 8 being connected to a suitable discharge pump 9.

[0030] As it can be seen, the device 6 is housed outside the washing tub 7, in a position away from it; moreover, according to the given example, the device 6 is placed slightly higher than the bottom of the tub 7.

[0031] The tub 7 is also in communication with a proper washing or re-circulating pump P, which supplies one or more spraying elements I with the liquid collected from the bottom of the tub 7; also the above spraying elements and the washing pump are per-se known for their manufacture and operation, so they will not be further described here in detail.

[0032] Fig. 2 shows schematically a possible embodiment of the dosage device 6; in this figure the portion of the conduit 2 from the softening device 5 has a different shape compared to the one illustrated in Fig. 1; however, the operation of the device 6 is substantially similar in both embodiments.

[0033] The device 6 comprises a body 11 made of plastic material, for example consisting of two hot blade welded polypropylene shells, wherein a connector is defined, being indicated with R as a whole.

[0034] The connector R has a first connection 12 to the conduit 2 and a second connection 13 to the tube T; as it can be seen, the connection 12 and the tube 2 have a smaller section compared to the connection 13 and the tube T.

[0035] Three ducts are delimited between the connectors 12, 13 and the body 11, i.e.:

• a first duct C1, for connecting the conduit 2 to the tube T, i.e. the outlet of the connection 12 with the inlet of the connection 13;
• a second duct C2, for a direct connection of the area surrounding the duct C1 with a first and a second chambers 16A and 16B, being delimited within the body of the device 6;
• a third duct C3, for connecting the upper part of the connector 13, and consequently the tube T, with a third chamber 16C being defined within the body of the device 6.

[0036] The two chambers 16A and 16B communicate in their lower part with the duct C2 and are open upwards (i.e. in communication with the atmosphere); also the chamber 16C is open upwards, but isolated with respect to the chambers 16A and 16B.

[0037] Fig. 3 shows schematically a front view of the connector R, where ducts C1, C2 and C3 can be seen; in this figure a seat indicated with S is provided, for fastening a non-return valve, indicated with V in Fig. 2, which is assembled on the connection 13.

[0038] The valve V, shown as a side and front view in Fig. 4, essentially consists of a rubber element or analogous material with a peripheral ring V1, which is apt for elastic coupling with the seat S of the connector R, and a central part V2, which in its rest position is at least apt to close ducts C1 and C2 with respect to the connector 13; V3 indicates spaced edges connecting the central portion V2 to the peripheral ring V1; V4 indicates openings being present on the peripheral ring V1; the duct C3 will never be completely closed by the central portion V2, due to the dimensions of the central section V2 and the presence of the spaced edges V3 and the openings V4.

[0039] The flexibility of the edges V3 is high enough to let the central portion V2 to move from a closed position (Fig. 5) to an open position (Fig. 2), under the water thrust through the connector R, as it will be clear in the following.

[0040] Back to Fig. 2, references 17A and 17B indicate two floats, made from a polymer, which are inserted in chambers 165A and 16B, respectively and are apt to slide within them; according to an important aspect of the present invention, the floats 17A and 17B have a ball or spherical shape, made for instance of polypropylene or blown and tumbled polystyrene.

[0041] References 18A and 18B indicate two electric micro-switches, whose type and operation are commonly known, fastened in the upper section of the body 11.

[0042] The micro-switches 18A and 18B have respective control rods 19A and 19B, which are apt to be moved by the balls 17A and 17B, and tend to raise up in the chambers 16A and 16B during the water filling steps of the washing tub 6, as further detailed.

[0043] As it can be seen, the ball 17A and the micro-switch 18A are provided for the level control of the liquid supplied to the tub 7, whereas the ball 17B and the micro-switch 18B are provided for safety purposes, should the first micro-switch 18A fail to operate. To this purpose, as it can be seen, the rod 19B of the micro-switch 18B is arranged for switching at a higher limit, i.e. a safety limit, which is higher compared to the position and threshold of the micro-switch 18A and its relevant rod 19A.

[0044] The operation of the machine being illustrated in Fig. 1 is as follows.

[0045] When the dishwasher user starts a wash cycle in a known way, a programmer device or timer (not represented for simplicity's sake) actuates the opening of the solenoid valve 3.

[0046] Water from the mains enters the softening device 5 after overcoming the air breaker 4; water exiting the softening device 5, i.e. filtered and softened, is conveyed to the connector R of the device 6, and namely to the connector 12.

[0047] Water flows through the connector 12 and then further along the duct C1, in the direction of the arrow F of Fig. 1, so causing the valve V to open in the position illustrated in Fig. 2.

[0048] Water can then pass in the connector 13 and further along the tube T, so reaching the washing tub 7, which is gradually filled with water.

[0049] The gradual raising of the water level the tub 7 is transferred, through the same tube T and by virtue of the duct C2, also to the chambers 16A and 16B, which are gradually filled up; such a filling up also determines a gradual raising of the balls 17A and 17B in the relevant chambers 16A and 16B.

[0050] The water supply to the tub 7 continues until the ball 17A shifts the rod 19A of a preset angle, causing the micro-switch 18A to switch. This switching constitutes a control signal for stopping the electric supply of the solenoid valve 3, and therefore make it to close. Therefore, under this condition, the tub results in being filled up to a predetermined water level, depending on the operation threshold determined by the work position of the micro-switch 18A.

[0051] Moreover, the function of said control signal is also to let the electric motor of the machine programmer or timer to start again (during the water supply from the mains, said motor is typically at standstill), for enabling the execution of the subsequent phases being provided by the washing cycle.

[0052] Following said water flow stop, the valve V goes back to its initial rest position, so closing the connector 13 as illustrated in Fig. 5. As it can be seen, the valve V is maintained in its closed position not only by the elastic force of the edges V3, but also and above all by the water pressure tending to raise up in the tube T, in the direction of the arrow F.

[0053] Under this condition of connector 13 being closed, every substantial back-flow of dirty water to the device 6, as well as possible contamination of the dosage chambers 16A and 16B, is prevented.

[0054] Should the micro-switch 18A fail to operate, for example due to a likely malfunction, water will still be supplied to the tub 7 and determine a further increase of the level in the chambers 16A and 16B. In such an event, the supply of water to the tub 7 continues until the ball 17B comes in contact with the rod 19B and shifts it of a preset angle, so causing the micro-switch 18B to switch. Then, also in this instance, the switching generates a signal, or an electric supply interruption, which is apt to cause the closure of the solenoid valve 3. Such a signal can be possibly used also to control the operation of the pump 9 shown in Fig. 1, for discharging any excess water from the tub 7, or operate a second solenoid valve possibly provided for safety purposes along the conduit 2. Finally, this signal may also be used to operate a visual and/or acoustic alarm for the user.

[0055] Thus, the micro-switch 18B operates to hinder the water Level in the tub 7 from exceeding a predetermined safety limit, being defined by the operation threshold of the micro-switch 18B itself, to avoid a possible flooding.

[0056] At any rate, the operation of the valve V, should the micro-switch 18B switch in, is similar to the one described above.

[0057] As it can be realized, when the washing liquid is discharged from the tub 7, the water level inside the chambers 16A and 16B gradually decreases until the whole amount of liquid is fully discharged.

[0058] This determines a gradual lowering of the balls 17A and 17B to their initial position, as shown in Fig. 2, so causing a consequent "resetting" of the micro-switch 18A (and possibly of the micro-switch 18B, should the above discharge be subsequent to a safety operation of the device).

[0059] Said "resetting" of the micro-switches which follows a water discharge is not necessarily such to automatically enable a new opening of the solenoid valve 3, since the latter is anyway also subject to the control of the dishwasher programmer.

[0060] The chamber 16C and its relevant duct C3 are advantageously employed in washing machines, in particular dishwashing machines provided with the so-called "dynamic" water supply or water dosage systems, i.e. such systems where the washing pump is activated before the water supply from the mains has ended.

[0061] In this kind of application, the preset level detected on the tub bottom for closing the supply solenoid valve equals a water volume actually smaller than the one being present in the hydraulic circuit of the dishwasher; under this condition, in fact, some liquid is circulating through the washing pump and the relevant spraying elements.

[0062] Therefore, should for any reason the washing cycle be interrupted (for example the user opens the machine door to add more crockery for washing), then the washing pump would stop and the water within the spraying circuit fall down to the tub bottom, with its consequent level increase.

[0063] In such events, some air may collect in the liquid supply conduit to the tub, due to its gradual filling up during the normal supply (reference can made to what has been explained in connection with the air-breaker device mentioned at the beginning of the present description); this bag of air may hinder the level increase, due to the washing cycle having been stopped, from being released in the liquid supply conduit to the tub. Therefore, under some circumstances, such a level increase may determie a liquid overflow from the tub.

[0064] According to the present invention, on the contrary, the liquid in the spraying circuit falling down will surely determine a water back-flow along the tube T, which fact is possible due to the presence of duct C3.

[0065] In fact, the air possibly collected in the tube T is free to flow out from the duct C3, due to the thrust of the liquid raising within the same tube T, towards the chamber 16C, but without any contamination risks for the chambers 16A and 16B, which are isolated by the valve V. As said above, such a valve V is designed to close ducts C1 and C2 but not duct C3, not even under the condition represented in Fig. 5.

[0066] The dishwasher hydraulic circuit may possibly be so designed that when the washing cycle is interrupted as mentioned above, a portion of the liquid raising up along the tube T can reach the chamber 16C; it should be appreciated that no particular problems exist if such a liquid contains some dirt rests, as the chamber 16C is not used for dosage purposes and contains no means for this purpose, such as floats and micro-switches.

[0067] Anyway, when the washing cycle is subsequently restarted (as, in the above mentioned example, closing the machine door), the washing pump operates again sucking the water collected on the tub bottom and recalling also the water possibly in excess within the tube T and in the chamber 16C.

[0068] In the preferred embodiment of the present invention, the operating point of micro-switches 18A and 18B, as well as the micro-switches themselves (but not the control rods end), are placed at a higher level compared to the water overflow height (N - Fig. 1), i.e. the highest level over which water can flow out from the tub 7 in case of a event of failure of the supply and dosage system, or of the solenoid valve 3.

[0069] Therefore, since micro-switches 18A and 18B are placed on a high position, the use of balls 17A and 17B with big dimensions (preferably a diameter in the order of 18-30 mm) and selection of rods 19A and 19B of a certain length, will let the live parts (i.e. the micro-switches themselves) to be spaced from the water supplied to the device 6, thus avoiding a likely contact of the overflow water from the tub 7 with them.

[0070] To this purpose, it will be appreciated how the operation point of the micro-switches may be advantageously raised further up, simply providing more than one ball inside each chamber 16A and/or 16B.

[0071] Moreover, according to a significant aspect of the present invention, frictions determined by the ball configuration of both floats 17A and 17B in the respective flowing chambers 16A and 16B will be much smaller than that determined by substantially cylindrical or parallelepiped floats, used so far in known dosage devices, as explained initially; in this way, fault or jam-up risks are reduced; for the same reasons, the ball or spherical configuration of the floats according to the present invention ensures a consistent thrust on the micro-switch actuation rods.

[0072] Thanks to its intrinsic features, the spherical structure also avoids possible alterations of the float external shape (the so-called "warping"), which may occur in the known devices due to their extended use.

[0073] A substantial advantage of a spherical configuration for the floats is their "self-cleaning" capability; in other words, during their motional steps, the ball floats tend naturally to rotate around their geometrical center and become free from likely soil deposits on them.

[0074] As mentioned above, the presence of duct C3 and chamber 16C proves particularly advantageous for washing machines fitted with dynamic water intake systems.

[0075] However, the present invention can also be advantageously applied to machines fitted with a static intake system, i.e. where the washing pump starts operating only at the end of the liquid dosage step. For such applications, both the duct C3 and chamber 16C may not be strictly required, since there is no risk of a liquid level increase in the tub caused by any interruptions of the washing cycle.

[0076] In such an event, when the opening of the solenoid valve 3 is shut through the timer control, also the non-return valve V will close, as explained in the foregoing, avoiding likely back-flows of impurities inside the device 6.

[0077] In such events, anyway, it should be appreciated that, upon interruption of the flow, the air possibly present will collect right between the water in the tube T and the valve V; such a bag of air will then form a good "barrier" of its own, against a liquid and likely impurities back-flow to the device 6. At any rate, availability of the valve V is a warranty against any contamination risks of chambers 16A and 16B and of the floats contained therein.

[0078] From the above description the features of the present invention are clear.

[0079] In particular, a device has been described, for the liquid supply and dosage into the tub of a domestic washing-machine, particularly a dishwasher, where the liquid dosage is obtained through the detection of the level of the liquid being present within the tub; the device comprises detection means located outside the tub 7, which operate on the basis of the quantity of liquid supplied to the tub, a conduit being provided to let such detection means communicate with the tub.

[0080] According to the present invention, closure means are provided to shut said conduit following the intervention of the detection means, or at the end of a liquid supply step to the tub, in order to prevent the substantial liquid back-flow from the tub to the detection means.

[0081] The detection means may comprise floats, which are apt to switch electric contacts for stopping the liquid supply to the tub, said floats being housed in respective chambers delimited in the body of the device; such a body is hydraulically connected to the tub, so that the gradual raising of the liquid level in the tub determines a consequent raising of a float in the respective chamber, which occurs gradually until producing the switching of a contact, the switching threshold of the contact corresponding to the achievement of a predetermined level of the liquid within the tub. The float or floats used to this purpose preferably have a ball or spherical configuration.

[0082] In the preferred embodiment of the invention, the closure means comprise a non-return valve, particularly made of elastic material and/or actuated by the liquid itself.

[0083] According to an important aspect of the present invention, vent means are provided which, also after the intervention of the detection means, are apt to allow the liquid return from the tub to said conduit, specifically in the instance of dynamic liquid supply systems. Such vent means comprise at least a duct for constant connection of said conduit with the atmosphere, independently from the operating condition of said closure means, and a chamber delimited in the device body.

[0084] From the above description, also the advantages of the present invention are clear. In particular, the following points are highlighted:

• the easy operation, since the water dosage in the tub is based on the use of floats and micro-switches;
• the simple manufacturing, since the device comprises high repeatable components in the manufacturing process, having a long mechanical life, i.e. ball or spherical floats and micro-switches usually warranted for thousands of switching cycles; similarly, the body of the device according to the invention is obtained through a simple thermoplastic molding or hot blade welding operation;
• the presence of means apt to hinder a back-flow of contaminated water to the device allows for an increase in the efficiency of the device and its reliability with time;
• the compact and reduced overall dimensions;
• the presence of a vent formed by the duct C3 and the open chamber 16C hinders water overflow problems from the tub, should the washing cycle be interrupted, in those machines fitted with dynamic water supply systems;
• the detection reliability, since the ball configuration of the float undergoes much smaller frictions inside the relevant chambers, compared to the floats so far employed in the known solutions, with a consequent reduction of any error or jamming risks; for the same reasons, the ball configuration of the float warrants a consistent thrust on the micro-switch actuation rod;
• the ball configuration prevents possible alterations of the external shape of the floats (so-called "warping") caused by an extended use, thanks to the specific features of the ball configuration; moreover, it also allows a for obtaining a "self-cleaning" action of the floats, which during their motional steps tend naturally to rotate around their geometrical center and become free from likely soil deposits on them;
• for the above reasons, more than one float may be housed in one same chamber; which facts would not be recommended for reliability reasons in the instance of cylindrical or parallelepiped floats according to the known state of the art;
• ball structures suitable for the use in the device according to the present invention are common and easy to find on the market, i.e. they are low-cost items.

[0085] It is obvious that many changes are possible for the man skilled in the art to the liquid supply and dosage device in the tub of a domestic washing machine, particularly a dishwasher, described above by way of example, without departing from the novelty spirit of the innovative idea.

Claims

1. A device for the liquid supply and dosage in the tub (7) of a domestic washing-machine tub, in particular a dishwasher, wherein the liquid dosage is realized by detecting the level of the liquid being present within the tub (7), said device (6) comprising detection means (16A,16B,17A,17B,18A,18B,19A,19B) located outside the tab (7) and operating on the basis of the amount of liquid supplied in the tub, a conduit (C2,13,T) being provided to put said detection means (16A,16B,17A,17B,18A,18B,19A,19B) in communication with said tub (7), characterized in that closure means (V) are provided, for shutting said duct (C2,13,T) at the end of a liquid supply operation in the tub (7), so as to prevent the substantial liquid return from said tub (7) towards said detection means (16A,16B,17A,17B,18A,18B,19A, 19B).

2. A device, according to claim 1, characterized in that said detection means (16A,16B,17A,17B,18A,18B,19A,19B) comprise at least a first float (17A) apt to determine the switching of a first electric contact (18A) for stopping the liquid supply to the tub (7).

3. A device, according to claim 2, characterized in that said first float (17A) is housed in a first chamber (16A) being defined in a body (11) of said device (6).

4. A device, according to claim 3, characterized in that said body (11) is hydraulically connected to the tub (7) in a way that the gradual raising of the level of the liquid in the tub (7) determines a consequent raising of the first float (17A) in the first chamber (16A), which occurs gradually until the switching of said first contact (18A) is caused, the switching threshold of said first contact (18A) corresponding to the achievement of a first predetermined level of liquid within the tub (7).

5. A device, according to claim 1, characterized in that said closure means (V) comprise a non-return valve (V).

6. A device, according to claim 1 or 5, characterized in that said closure means (V) are made of elastic material, such as rubber or similar material.

7. A device, according to claim 1 or 5, characterized in that said closure means (V) are actuated by means of the liquid being present in said conduit (C2,13,T).

8. A device, according to claim 2, characterized in that said first float (17A) has a ball or spherical shape.

9. A device, according to claim 1, characterized in that vent means (C3,16C) are provided, which, also at the end of a step of liquid supply to the tub (7), are apt to let the liquid from the tub (7) to flow back to said conduit (C2, 13, T), particularly in the instance of dynamic liquid supply systems.

10. A device, according to claim 9, characterized in that said vent means (C3,16C) comprise at least a duct (C3) constantly connecting said conduit (C2, 13, T) with the atmosphere, independently from the operating condition of said closure means (V).

11. A device, according to claim 10, characterized in that said vent means (C3,16C) comprise a second chamber (16C) being defined in the body (11) of said device (6) and connected with said duct (C3).

12. A device, according to claim 1, characterized in that hydraulic connection means (R) are provided between said body (11) and said tub (7), which comprise a connection (R) having an inlet (12) and an outlet (13), the inlet being connected to a liquid supply line (2) and the outlet being connected to said conduit (C2, 13, T).

13. A device, according to the previous claim, characterized in that between said connections (12,13) a second duct (C2) is delimited, which is apt to put said outlet (13) in direct communication with said first chamber (16A).

14. A device, according to the previous claim, characterized in that said second duct (C3) departs from said connection (R).

15. A device, according to at least one of the previous claims, characterized in that said detection means (16A,16B,17A,17B,18A,18B,19A,19B) comprise at least a third chamber (16B) being defined in said body (11), for housing at least a second float (17B), which is apt to cause the switching of a second electric contact (18B), said third chamber (16B) being hydraulically connected to the tub (7), so that the gradual raising of the level of the liquid in the tub (7) determine a consequent raising of the second float (17B) in the third chamber (16B), which occurs gradually until the switching of the second contact (18B) is determined, the switching threshold of said second contact (18B) corresponding to the achievement of a second predetermined level of the liquid within the tub (7).

16. A device, according to the previous claim, characterized in that also said second float (17B) has a ball or spherical shape.

17. A device, according to claim 15 or 16, characterized in that said third chamber (16B), said second float (17B) and said second contact (18B) are provided for safety purposes, should said first contact (18A) fail to operate, the switching threshold of said second contact (18B) being at a higher level compared to the switching threshold of said first contact (18A).

18. A device, according to one or more of the previous claims, characterized in that at least one of said contacts is a micro-switch (18A , 18B) having a control rod (19A, 19B) apt to be shifted by said float (17A, 17B).

19. A device, according to one or more of the previous claims, characterized in that at least two ball floats are provided within one same chamber.

20. A method for the supply and dosage of liquid in the tub (7) of a domestic washing-machine, in particular a dishwasher, wherein the liquid dosage is realized by detecting the level of the liquid being present within the tub (7) through a device (6) which comprises detection means (16A,16B,17A,17B,18A,18B,19A,19B) located outside the tub (7) and operating on the basis of the amount of liquid supplied to the tub, a conduit (C2,13,T) being provided to put said detection means (16A,16B,17A,17B,18A,18B,19A,19B) in communication with said tub (7), characterized in that, following the intervention of said detection means (16A,16B,17A,17B,18A,18B,19A,19B), the shutting of said conduit (C2,13,T) is produced, in order to prevent the substantial back-flow of liquid from said tub (7) towards said detection means (16A,16B,17A,17B,18A,18B,19A,19B).

21. A method, according to claim 20, characterized in that the return of liquid from the tub (7) into said conduit (C2,13,T) is allowed also following the intervention of said detection means (16A,16B,17A,17B,18A,18B,19A,19B), particularly in the instance of dynamic liquid supply systems.

Drawing