Patent Publication Number: US-7713358-B2

Title: Dishwashing machine with a gradual-start wash cycle

Description:
TECHNICAL FIELD 
     The present application relates to a dishwashing machine with a gradual-start wash cycle. 
     BACKGROUND 
     In the dishwashers used in restaurants, the washing cycle start-up is always a critical moment because of the high water temperature (55-60° C.), which from the washing tank is circulated by the pump nearly instantaneously. Such action can cause both a high vacuum inside the tank and a sudden emission of steam outside the machine. 
     There are known various systems which are based on the reduction of the number of revolutions of the recirculation pump during the first moments of the washing cycle. Such systems are particularly costly and difficult to apply to high power pumps. 
     It would be desirable to obtain a dishwashing machine capable of simply and cost-effectively solving the drawbacks of the prior art. 
     SUMMARY 
     In one respect, a dishwashing machine includes a wash water tank, a plurality of wash water dispensing nozzles and a recirculation pump adapted to circulate wash water from the tank to the nozzles. The dishwashing machine is characterised in that it includes hydraulic filling means presenting an inlet aperture and an outlet aperture and connected to a first and a second conduit at the apertures; the first and second conduit being connected respectively to a delivery conduit and to a suction conduit of the pump. 
     The outlet aperture and the inlet aperture may be arranged in a reciprocally offset fashion. 
     In another aspect, a water dispensing method in a washing cycle of a dishwashing machine involves in sequence a cavitation step in which a circulation pump circulates a mixture of wash water and air, and a full capacity pumping step in which the recirculation pump circulates only wash water. 
     The cavitation step may comprise an auxiliary pumping operation in which the recirculation pump intakes air from a hydraulic filling means and outputs a wash water/air mixture into the filling container; the auxiliary pumping operation causing a gradual filling of the hydraulic filling means with consequent end of the cavitation step. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The description that follows is given by way of a non-limitative example for a better understanding of the present invention with reference to the accompanying drawing which schematically shows one embodiment of a washing station of a dishwashing machine. 
     
    
    
     DETAILED DESCRIPTION 
     In the FIGURE it is shown as a whole with numeral  1  a washing station of a dishwashing machine. 
     The washing station  1  includes a tank  2  for the wash water, a plurality of dispensing nozzles  3  located on upper and lower dispensing arms  4 , and a recirculation pump  5 , which is connected to the tank  2  via a suction conduit  6  and to the dispensing arms  4  via a delivery conduit  7 . 
     The washing station  1  includes hydraulic filling means consisting of a filling container  8  presenting an inlet aperture  9  located in a bottom portion  8   a , and an outlet aperture  10  located in a side portion  88   b . At the inlet  9  and outlet  10  apertures, schematised with a rectangle in the FIGURE, the filling container  8  is connected to a first and a second conduit  11 ,  12 , in turn connected respectively to the delivery conduit  7  and to the suction conduit  6  of the pump  5 . 
     In particular, in the FIGURE, the conduit  11  and the conduit  12  are shown respectively with a broken and solid line with an arrow indicating the direction of circulation of the fluid. 
     The filling container  8  presents, furthermore, a vent aperture  13 , also schematically shown with a rectangle and located in an upper portion  8   c . The filling container  8 , at the vent aperture  13 , is connected to a vent conduit  14 , which discharges directly into the tank  2 . 
     The vent conduit  14  is shown both with a broken and a solid line and with a double arrow, indicating that in this conduit the fluid can advance in either direction according to the circumstances, as described below. 
     The filling container  8  and the conduits  11 ,  12  and  14  can be formed integrally as a unitary body or separately. Furthermore, the machine may include closing systems for the apertures  9 ,  10  and  13 . 
     The apertures of the filling container  8  and the conduit connected thereto are dimensioned so to realize in the filling container  8  itself the inequality due to which the water flow rate in excess, let out through the vent conduit  14 , is lower than the water flow rate from the inlet aperture  9  by a certain value in consequence of which the recirculation pump  5  intakes only water and not an air/water mixture. In this way, it is guaranteed that in the container  8  the suction flow rate is lower than the delivery flow rate, and that it is such, therefore, not to re-establish the cavitation phenomenon during the full capacity pumping step. 
     In use, the filling container  8  is initially empty of water and is positioned at a height slightly higher than the maximum level that the wash water can reach in the tank  2 . With the filling container in this position, the recirculation pump  5  is operated, which, in addition to taking the wash water from the tank  2 , intakes the air present in the container  8  through the conduit  12  and, in addition to circulating the water/air mixture in its delivery conduit  7 , introduces the air/water mixture into the container  8  through the conduit  11 . This action causes the cavitation phenomenon of the wash water and, therefore, a decrease of the pressure at the delivery nozzles  3 . 
     The cavitation step ends after the filling container  8  fills with wash water to a level such that the outlet aperture  10  is covered. From this moment on, the pump  5  takes not air but wash water from the filling container  8  and starts a full capacity pumping step. 
     From the above, it is apparent how the duration of the cavitation step depends on the volume of the filling container. 
     The aperture  13  and the vent conduit  14  allow the suction of air during the cavitation step, the discharge of air bubbles present in the pump and, when the pump is not running, the emptying of the filling container  8  at the consequent reinstatement of the circuit. 
     The described dishwashing machine simply and cost-effectively avoids the sudden circulation of high temperature pressurized water. Furthermore, the adopted solution is applicable to all recirculation pumps without power limitations.