EP0547011B1

EP0547011B1 - A washing method for a dishwashing machine of industrial type

Info

Publication number: EP0547011B1
Application number: EP92830661A
Authority: EP
Inventors: Liano Maffei; Elio Lippi
Original assignee: COLGED Srl
Current assignee: Premark International Holdings BV
Priority date: 1991-12-11
Filing date: 1992-12-10
Publication date: 1997-02-26
Anticipated expiration: 2012-12-10
Also published as: ES2100330T3; DE69217629T2; IT1252886B; EP0547011A1; ITFI910293A1; DE69217629D1; ITFI910293A0

Description

The present invention relates to a washing method for dishwashing machines of industrial type, in particular for bars, restaurants and cafeterias.
The dishwashing machines for bars, restaurants and cafeterias presently on the market, comprise a tank containing washing liquid circulated by a motor-driven pump which sprays said liquid under pressure at the dishes at a temperature between 50 and 60°C. The washing liquid formed by water and detergent, with the residues removed from the dishes, falls after each spraying into the tank and is recirculated by means of the pump until the end of the washing cycle, usually lasting 60 to 180 seconds, when the washing liquid is partially renewed with about 3 lt of clean water from the rinsing which takes place at a temperature of about 80-90°C by means of an independent circuit and for a duration of about 10-20 seconds.
In the dishwashing machine according to DE-A-4006621 independent washing and rinsing circuits are provided but the rinsing water is mixed with some of the washing water to constitute the washing water for a successive cycle.
These dishwashing machines, though widely used and efficient, have, from a hygienic point of view, the serious inconvenience of using a washing liquid which becomes continually more polluted with food residues, full of bacteria and other pathogenic agents, with each new cycle in which they are reused. In fact the about 3 lt of clean water added for each rinsing are absolutely not sufficient to keep the washing liquid under a certain level of pollution as the number of cycles increases.
To eliminate this inconvenience, small dishwashing machines have been proposed with a washing circuit independent from the rinsing circuit in which the washing liquid is completely discharged at the end of each cycle and replaced with the rinsing water which, after its make-up if any, is used for the subsequent washing. In particular, small washing machines for glasses and cups, operating according to this principle have been realized by the same applicant, for instance for bars, having a small pump with jets of water shooting only upwards and able to wash with only 3-4 lt of water.
Dishwashing machines operating in this way, but of greater capacity, have not however been realized since they have the considerable limitation of requiring for each cycle a great amount of water for a satisfactory operation of the pump and to allow the spraying of the dishes from several directions to assure a good washing. It would therefore be uneconomical, even though more hygienic, to renew all the washing water at each cycle since the consumption of energy would become too great and the power that would have to be installed would be considerably higher than that of normal dishwashers and incompatible with the normally available electric power supply.
A system for maintaining at a low level the water consumption is disclosed in FR-A-2443231, where a dishwashing machine of the single circuit type is described. The washing circuit, in correspondence to the branching between upper and lower spraying means, is provided with a distributing valve that conveys the detergent liquid flow alternatively toward the lower and the upper spraying means respectively.
The object of the present invention is to provide a washing method for a dishwashing machine of industrial type, in particular for restaurants and cafeterias, which requires a small amount of washing water and therefore makes the replacement of all the washing liquid at the end of each cycle inexpensive while providing evident gains in terms of hygiene. All of this without lowering noticeably the performance of the machine in terms of time and detergent efficiency as compared to a conventional dishwasher.
The features of the method according to the present invention are as defined in claim 1.
Further characteristics and advantages of the method for dishwashing machines according to the invention will be more apparent in the description which follows of one of its possible embodiments, given as an example but not limitative, with reference to the attached drawings in which:

Figure 1 is a schematic view of a dishwashing machine;
Figure 2 is a sectional view executed according to a vertical plane of a distributing valve of the machine in figure 1;
Figure 3 shows a possible temporal scheme for the steps of the method according to the invention.

With reference to figure 1, a dishwashing machine comprises a washing chamber 1 in which there is housed a dish rack 2 resting above a collecting tank 3 of the detergent liquid or of the rinse water, a circulation pump 4 of the detergent liquid connected to a first circuit 5 which branches into lower 6 and upper 7 suppliers having respectively a battery of lower 6a and upper 7a sprayers. The rinsing is assured by a second circuit 8 connected in 9 to a water supply network either directly or through a motor-driven pump not shown and comprising a solenoid valve 10 which sends the water to a heater 11 comprising a heating element 11a and connected to a battery of sprayers 12 for rinsing. A bypass 8a crossing a solenoid valve 10a puts the supply network, connected at 9 to the machine, in direct communication with the sprayers 12 excluding the heater 11 when a pre-rinsing of the dishes with unheated water is requested. In the tank 3 a resistor 13 is provided for the heat control of the washing liquid, a filter 3a for the filtering out of solid residues and, below, a discharge pump 14 for the elimination of the dirtied washing liquid before the rinsing.
With reference to figures 1 and 2, in correspondence with the branching between the upper and lower suppliers 6 and 7 and the first circuit 5, a three-way distributing valve 15 is provided for with a clapet 15a operated by a hydraulic plunger 16 controlled by a solenoid valve not shown. Alternatively mechanical or electromechanical operation can be provided for.
With reference to figure 3, the washing cycle which results from the method according to the invention is completed in time T. Initially, detergent liquid is sprayed, for example, upwards against the dishes for a time T1. In a time T5 the flow of the detergent liquid is then inverted to spray downward for a time T2 at the end of which the discharge of the detergent liquid polluted with residues removed from the dishes in time T4 is carried out. At the end of said discharge, the second circuit which carries out the rinsing in time T6 is opened. At the end of the rinsing a subsequent washing can begin repeating the cycle for a time T which begins with a washing from below after the inversion in time T3 of the flow of the detergent liquid towards the lower sprayers 6a. The detergent liquid for the subsequent washing is obtained from the rinse water, supplied in time T6, to which detergent is added as well as, possibly at a later point, water taken from the supply network, which can be cold network water or, if available, water preheated to about 50°C, in order to reach the minimum quantity of detergent liquid necessary for the washing.
Strictly as an example the times of a washing cycle can be: T=138s, T3=4s, T1=50s, T5=3s, T2=55s, T4=9s, T6=17 s.
The sequence of washing just illustrated, wherein the spraying upwards precedes that of downwards, can be inverted, just as more than one downward or upward spraying can be repeated in sequence in a single washing cycle. The relationship between the duration of the upwards and downwards washings can also vary as a function of the type of dish to be washed. In particular for cups and glasses an upwards washing lasting longer than that necessary for plates is more efficient.
With reference to the above mentioned figures, the suppliers 6 through the sprayers 6a spray water upwards for a time T1 due to the raised position of the clapet 15a of the valve 15. This is possible thanks to the plunger 16 which, hydraulically controlled in time T3, keeps the clapet 15a raised. Upon the withdrawal of the plunger 16, which occurs after a time T3' following a pause in the operation T5 of the pump 4, the clapet 15a is lowered by the force of gravity inverting the flow of the detergent liquid which, conveyed through the circuit 5 as well as through the suppliers 7 and the sprayers 7a at the resumption of the operation of the pump 4 itself, is sprayed downwards for a time T2. At the end of time T2, the pump 4 stops and the pump 14 precedes with the discharge of the detergent liquid contained in the tank 3 and polluted by food residues from the washing. The plunger 16 can also withdraw at the end of time T3, since the water which arrives under pressure from the pump 4 keeps the clapet 15a raised likewise allowing the downward spraying until the pause T5.
Advantageously in time T6 a pre-rinse can be executed with water taken directly from the supply network through a bypass 8a following the opening of the solenoid valve 10a which is followed by the actual rinsing, already described, with water heated to between 80 and 90°C.
Once the detergent liquid is discharged and the solenoid valve 10 activated, the rinsing begins by means of the suppliers 12 to which very hot water arrives after passing through the heater 11. The rinse water again fills the tank 3 and, along with the detergent and any water to be added in order to arrive at the minimum quantity (about 6 lt), is used for forming the detergent liquid for the subsequent cycle which begins with the lifting of the clapet 15a and the starting of the pump 4.
All the above-described washing operations, discharge, rinse, etc. are controlled by a timer in a conventional way not shown.
During the washing the water is maintained at a temperature of about 55° by the resistor 13 in the tank 3. The water in the heater 11 (normally 5 to 6 lt) is brought to rinsing temperature during the washing and then partially replaced with water coming from the network at the rinsing.
The washing, alternated between upwards and downwards, allows the reduction by about 50% of the volume of wash water necessary with the possibility of renewing at each washing cycle the detergent liquid present in the tank 3. The washing time is not doubled with respect to a cycle carried out by a traditional dishwashing machine since during the washing with the lower sprayers the detergent liquid hits the dishes from below and then falls under the force of gravity towards the tank 3 allowing the more resistent residues present on the dishes to soften before then finally being removed by the upper sprayers during the downward spraying.
The washing is thus accomplished with a detergent liquid which is always clean assuring the maximum hygiene without requiring a great increase in the amount of energy used with respect to a traditional dishwashing machine thus making the invention very competitive on the market.
It is worth noting that, in the same way as the washing step, also the rinsing step can be alternated utilizing a three-way valve positioned on the rinsing duct 8 in correspondence with the branching at the two groups of sprayers 12, in order to rinse the dishes with jets coming from below and then from above. Even lengthening the rinsing time by about 15 seconds, this way of operating proves advantageous in all cases in which the machine must be installed in an electrical power network of low capacity, insufficient to run the upper and lower sprayers contemporaneously. It also proves advantageous when an autonomous pump is provided for the rinsing circuit; in this case energy consumption is decreased as a result of the decreased total quantity of rinse water used.
The procedure according to the invention can be advantageously expanded also to traditional dishwashers in that it allows the use of a lower power pump.
Variations and/or modifications can be brought to the method according to the present invention without departing from the scope of the invention as claimed in the appending claims.

Claims

A washing method for a dishwashing machine of industrial type, in particular for restaurants and cafeterias, comprising the steps of:
- washing the dishes by means of jets of detergent liquid comprising hot water and detergent supplied and recirculated through a first circuit (5);

- rinsing the dishes by means of jets of clean water drawn from a supply network which is heated, conveyed and sprayed by means of a second circuit (8);

- said washing step comprising at least one step fraction in which the detergent liquid is sprayed only upwards and at least one step fraction in which the detergent liquid is sprayed only downwards; characterized in that, at the end of said washing step, all the detergent liquid entraining residues removed from the dishes is discharged and replaced by clean, hot rinse water, which, after a detergent addition forms the detergent liquid for the subsequent washing.
The washing method according to claim 1, wherein make-up water is added to the rinse water, said make-up water being drawn from the supply network through said second circuit (8) to form, with the detergent, the detergent liquid of a subsequent washing.
The washing method according to claim 2, wherein said make-up water to be added to the rinsing water is let in before the latter as a pre-rinse for the dishes.
The washing method according to the previous claims, wherein also the rinsing step occurs in at least one step fraction, wherein the clean water is supplied only upwards, and at least one step fraction wherein it is supplied only downwards.