LOW ENERGY, LOW WATER CONSUMPTION WAREWASHER AND METHOD

Abstract: A commercial warewasher is disclosed, in which racks (25) of soiled ware, such as dishes, are consecutively washed through a machine cycle which includes recirculating wash water over the ware followed by a fresh water spray rinse (32, 36). A portion of the wash water is drained and a second portion is intentionally retained in the machine during the rinse period after each rack of dishes is washed. The retained portion is thereby combined with the fresh rinse water to provide a volume of water sufficient for pumped wash recirculation for the next rack without cavitation, while enabling usage of a minimum quantity of rinse water required to provide effective rinsing. Reduced water consumption, reduced energy to heat the water and reduced chemical usage (detergents, sanitizers and rinse agents) are all possible in amounts and degrees depending upon the type and design of warewasher with which the method and apparatus is employed.

Description: This invention relates primarily to a warewasher for washing dishes, utensils, glasses and the like in commercial establishments such as restaurants, particularly "fast food" restaurants, and cafeterias. The terms warewasher and dishwasher may be used interchangeably herein. Further, the term commercial dishwasher (to which this invention is directed), is intended to distinguish from a "domestic" diswasher, the type commonly found in home use. Domestic and commercial dishwashers differ substantially in design and manner of use, with the possible exception of a few commercial machine styles which are an outgrowth of domestic unit designs. Even though these latter designs may appear similar in many respects, they differ in function and operation, not only in the length of time it takes to wash and rinse a rack of ware, but also in the number of washes and rinses per rack. Domestic units ordinarily have the further capability of drying washed dishes within the wash chamber, whereas comparable commercial units feature air drying outside the chamber in order to minimize the time it takes to complete each rack of ware. It is important in a commercial environment to wash racks successively in rapid order. Thus, a commercial washer is used for washing and rinsing but not for drying, because of the length of time it takes for the latter. Domestic dishwashers may operate as long as 60 to 90 minutes to complete washing, rinsing and drying a single rack of dishes per day, whereas in a commercial establishment, a dishwasher will wash and rinse a rack of dishes in two to three minutes or less, and require their immediate removal and replacement with the next rack. The cleansed ware is air dried in the racks, outside the dishwasher. It is rare, in a domestic environment, to wash consecutive racks or loads of dishes, whereas it is routine in the commercial environment, for example, where an operator may wash one rack after another of dishes during and after a lunch period at a restaurant. Most regular washing cycles of domestic machines include a substantial period for drying in the machine. In the commercial environment, racks of dishes or other ware are successively washed and rinsed in rapid fashion over a very short time cycle for each rack, typically of the order of two to three minutes. The kind of commercial dishwasher to which this invention is applicable is commonly referred to as a "stationary rack machine" i.e., a unit with an enclosable wash chamber in which a rack of dishes is placed, washed, rinsed, and then removed and replaced by a second rack of dishes, while the cleansed rack is air dried outside the chamber. There are two main types of stationary rack dishwashers, one type commonly referred to in the trade as a "fill-and-dump" (hereinafter "fill/dump") machine and a second type which has a large volume tank or reservoir, commonly called a "recirculating" machine, hereafter referred to as a "recirculating" or "tank" machine. In a fill/dump machine, a single batch of water is typically used for each rack of dishes to be washed, in the following fashion. A sump in the wash chamber is filled with water, detergent added to make wash water, and a rack of soiled dishes placed in the chamber. The wash water is recirculated by a pump through a wash arm or arms having spray nozzles which spray the ware under relatively high pressure to loosen and remove the soil from the dishes. A drain valve is then opened to drain the sump of wash water by gravity into a waste line, usually located in the floor of the restaurant or cafeteria kitchen. The drain valve is then closed and a water line is opened to fill the emptied sump with fresh rinse water. This rinse water is then recirculated by the same pump and wash arm to rinse the ware. Upon completion of rinsing, the rack of rinsed dishes is removed from the chamber, but the rinse water is retained to serve as the wash water for the next rack of dishes, and detergent is typically added either automatically or by hand before the next rack of soiled ware is loaded into the machine. Although the single batch of water is used as rinse water for one rack and then subsequently used as wash water for the next following rack, the end result (except for the first fill) is that one batch of water is used for each rack of dishes, but the filling and draining of water does not coincide with the beginning and end of a machine cycle. Examples of patents illustrating the type of dishwasher referred to herein are U S. Patent 4,088,l45 issued May 9, l978 to Tore H. Noren and U.S. Patent 4,2l8,264 issued August l9, l980 to George J. Federighi and George B. Federighi. A variation of this type of unit is illustrated in U.S. Patent 3,903,909 issued September 9, l975 to Tore H. Noren and George J. Federighi, in which the batch of fresh water is introduced through the wash system to flush the wash system. Although each of these patents shows a variety of different designs and functions, they essentially show the basics of a fill/dump machine, namely the recirculation of rinse water through the same instrumentalities that carried the wash water, and the subsequent use of the rinse water as wash water for the next rack of dishes. With such machines, it is necessary to add enough rinse water to serve as the proper volume of wash water for a next rack of dishes. Such machines need to add enough rinse water each cycle to satisfy the supply, without cavitation, of the pump which circulates the wash water and, in most designs, the rinse water as well. The amount is frequently stated as being at least 6.435 litres (1.7 gallons) of rinse water, but frequently exceeds 7.57 litres (2 gallons) and sometimes is as high as 11.355 litres (3 gallons) per rack. Quite a different scheme is used in the "recirculating" or "tank" dishwasher. The tank is a relatively large reservoir which is originally filled with as much as 60.56 litres (sixteen gallons) of water and enough detergent is supplied to provide the proper proportion of detergent-to-water for washing. This water or wash liquid is used over and over for washing successive racks with most of the same liquid. The liquid is somewhat diluted with fresh rinse water each cycle. A drain valve is located at the bottom of the tank. The valve is part of an open vertical standpipe which provides an overflow level near the top of the tank. A fresh water spray system rinses the rack of ware at the proper time in a cycle, after it has been washed by pumped recirculation of the large volume of wash water. A primary purpose for using the tank system is to provide a significant volume of wash water on the dishes, even though that water is reused and tends to get heavily soiled if not watched. The water is typically heated by a heater, and acts as a heat sink to maintain water temperature. A fresh water dedicated rinse is supplied to perform rinsing while the wash recirculation pump is off. By "dedicated" is meant that the rinse system is used to carry only fresh water and not transport soiled wash water. The rinse water descends to the top of the pool of wash water, and a fairly large percentage of the rinse water may overflow through the standpipe and out to the drain. The tank itself is ordinarily drained only every few hours, at which time the water in the reservoir is usually fairly soiled. Strainers are provided to catch any large particles of food or other material washed from the dishes and keep them from reaching the sump wash liquid. Detergent is replenished as needed. To drain the tank, the standpipe is lifted, and in so doing the entire large volume reservoir is drained by gravity into a floor drain. An example of the type of system described as a tank system is shown in U.S. Patent 4,439,242 issued March 27, 1984 to James P. Hadden. One advantage of the tank system over the fill/dump system is that as little as 4.542 to 5.299 litres (1.2 to 1.4 gallons) of rinse water needs to be used per rack. With the large volume of water available for pumped wash recirculation, rinse water added through the dedicated rinse system can be a minimum quantity required to do an effective rinsing job. In addition to these primary types of washers, there exists fill/dump machines which utilize fresh water, dedicated rinse systems of a type similar to those used in tank machines. Such machines are completely drained of wash water by gravity directly to a floor drain, and, as will be shown, are incapable of providing the energy and water savings of this invention, without specific modifications to achieve the intended objectives. These fill/dump machines require similar volumes of water per rack as the previously discussed fill/dump machines, to satisfy wash pump needs. In terms of water temperature, commercial dishwashers are available in what the trade refers to as low temperature and high temperature machines. This simply means that the rinse water temperature in a low temperature machine may be 54 to 60°C (130°-140°F), and a sanitizing agent is included, such as sodium hypochlorite (common household bleach). In the case of a high temperature machine, the rinse water has a minimum sanitizing temperature of 82°C (180°F) to meet public health standards in the United States. It should be understood that the invention disclosed and claimed herein is useful in either low temperature or high temperature machines if the objective of obtaining water and/or energy savings is achieved. The invention provides what may be considered a hybrid type of warewasher which employs certain of the advantages of a fill/dump unit without necessitating use of as much water and energy, and also is capable of having the water and energy savings advantages of a tank machine. It functions in certain respects like a tank machine, but uses cleaner wash water and avoids loss of any of the freshest and hottest water to a drain, as happens to some extent in a tank machine. The latter features are attributes of a fill/dump machine. For an understanding of the functioning of a machine according to the invention, certain requirements of a stationary rack commercial dishwasher should be addressed first, primarily as an example, and not a limitation. A typical recirculation pump for the wash system requires a minimum of about 5.678 litres (1.5 gallons) of water in the sump to prevent pump starvation due to cavitation. But 5.678 litres is not only borderline in the amount of water that needs to be recirculated onto the ware to do an effective washing job, it also fails to recognise that much water is out of the sump during wash recirculation. For example, the recirculating wash pump disclosed herein delivers 227 litres of water per minute (60 gallons/min) through a pair of wash arms and tubing connected thereto. The tubing and the arms themselves hold a substantial proportion of the 5.678 minimum litres required. That, coupled with the facts that spray is suspended in the chamber and water must drip from the dishes and sides of the wash chamber, means that 5.678 litres is ordinarily insufficient to supply a pump having such a large flow capacity. Fill/dump machines of the type which have been described above utilise anywhere from 6.435 to about 11.355 litres (1.7 to about 3 gallons) of water in order to satisfy the washing requirements of the wash system. To provide the larger volume of wash water according to the invention, there is deliberate retention of a portion of the wash water by preventing it from going to the waste line or drain upon completion of washing. While this is unsatisfactory for good rinsing results in most fill/dump machines known heretofore, retention of wash water at the end of a wash portion of a cycle permits an operation of what appears to be a fill/dump design of dishwasher in a manner somewhat like a recirculating tank-type system. This necessitates, however, the use of a dedicated fresh water rinse system, which is standard in many machines. But, due to retention of some wash water each cycle, the invention can accomplish both effective washing and rinsing with less water and energy usage. According to one aspect of the present invention, there is provided a method of washing and rinsing consecutive racks of ware as defined in claim 1. According to another aspect of the invention, there is provided a warewasher as claimed in claim 7. According to a further aspect of the invention, there is provided a warewasher as claimed in claim 12. In a preferred form, the invention involves retention of some wash water by preventing its being drained at the end of the wash portion of a cycle. A drain pump pumps out the sump water to a waste line which is located at a higher level than the sump, in one form of the invention. In many fast-food establishments, the kitchens are relatively small in comparison to those found in cafeterias and restaurants, where floor drains are commonly provided. Such fast-food kitchens have sinks and traps which are typically located above floor level. Clearly, the gravity drain machines are not usable as a practical matter in such a kitchen. By designing a fill/dump type machine for low, undercounter use, and pumping drain water from the sump to a higher level drain, it is readily feasible to avoid or prevent pumping out all of the drain water. This retained water, though soiled, can be added to the fresh water which is supplied by dedicated rinse nozzles for rinsing the ware, and thus become a larger volume of wash water for the next rack of ware. In so doing, it is possible to use less water for rinsing, of the order of 5.678 litres (1.5 gallons) per rack, collecting another 2.839 to 3.785 litres (0.75 to 1 gallon) of water via retention from the previous wash, and thus having almost 9.463 litres (2.5 gallons) of water available for pumped recirculation for the next wash. That 9.463 litres is adequate to supply the wash pump without cavitation, and in so doing, allows less water to be used for rinsing. This saves not only water, but also the expense of energy and detergents (and sanitizing chemicals in the case of a low temperature machine), since their proportions are necessarily related to the amount of water used per rack. In essence, in this preferred design, although 5.678 litres (1.5 gallons) of water is added to each cycle by rinsing, the wash recirculating pump is performing with perhaps 9.463 litres (2.5 gallons) of water, which is quite adequate to satisfy its needs to do an effective washing job. In a second preferred form of the invention, water is retained from the drained wash water where gravity draining to a floor drain is possible. The retention means may be part of the mechanical design, a timed gravity drain period to close the drain while an approximate predetermined portion is retained, or any other manner of achieving a desired controlled retention. It should be recognised that the quality of wash water retained may vary in either form of the invention, provided the desired objective of reduced water consumption is achieved. It is recognised that, in domestic or home dishwashers, practically all of which pump to a drain at a higher level than the dishwasher sump, some drain water will be retained from each batch. This water is retained because it is not possible to fully pump out of system, all of the water which is pumped to a level higher than the pump. The amount of water retained in the sump at the end of a complete wash, rinse and dry cycle is known in some designs to be of the order of 119 to 237 ml (0.5 to 1 cup). But that water does not serve any function of enabling reduction of water and energy for the next rack, the next day. In a domestic system, there may be two or three fresh water rinses added to the sump, recirculated and pumped out. Thus, the final rinse water is quite clear. On the contrary,in the present invention, the retained water is soiled. But that is absolutely harmless, because it will be used subsequently only as wash water and not rinse water, similar to the tank system previously described. To the extent that certain commercial dishwasher designs are patterned after a domestic design, a small volume of wash water may be retained in the sump, but, if anything, it is detrimental and therefore kept to the minimum possible. The detriment exists because that retained wash water is soiled and should not be recirculated as rinse water through the pump and wash arms. The method and dishwasher embodying the invention possess the advantage that the volume of rinse water and duration of rinsing may be approximately the minimum required to perform effective rinsing, which serves to conserve energy and water. However, the total retained wash water and collected rinse water combining in the sump provide, for a next following rack of ware, a wash water volume which is substantially in excess of that supplied by the rinse system alone. In order that the invention may be more readily understood, reference will now be made to the accompanying drawings, in which:- Fig. 1 is a frontal view of an undercounter commercial dishwasher incorporating the features of the invention, and including an optional preheating water tank; Fig. 2 is a side view of the dishwasher shown in Fig. 1, with part of the cabinet broken away to show details of the wash and rinse systems and associated plumbing; Fig. 3 illustrates a modification using a gravity drain; Figs. 4A and 4B are, together, a schematic electrical control circuit; and Fig. 5 is a timing diagram for the timer shown in the electrical diagram; and Fig. 6 shows a modification using separate recirculating and drain pumps; With certain exceptions which will be noted, the basic components of a dishwasher incorporating the present invention are known. Referring to Figs. l and 2, the dishwashing machine includes a washing/rinsing chamber l0 which is defined by a cabinet, usually formed of stainless steel panels and components, and including a top wall ll, side walls l2 and rear wall l4, and a front facing door l5, hinged at its lower end, as indicated at l6. The chamber l0 is vented to ambient pressure through labyrinth seals (not shown) near the top wall. The cabinet is supported upon legs l7 which provide the necessary clearance for the underside of the machine to permit cleaning beneath it as required by various local sanitation codes. At the bottom of the chamber, as part of the sloping bottom wall 20 of the cabinet, is a relatively small sump 22 which may have a removable strainer cover 23. It is possible that a large plumbing elbow can serve the function of a sump because of the use of an outlet pipe or tube extending therefrom, as described below. Above the bottom wall, rails 24 provide support for standard ware racks 25, loaded with ware to be washed and sanitized, which are loaded and unloaded through the front door. A coaxial fitting 27 is supported on the lower wall 20, centrally of the chamber, and this fitting in turn provides support for a lower wash arm 30 and lower rinse arm 32, each of conventional reaction type. An upper wash arm 34 and upper rinse spray heads 36 are supported from the top wall of the chamber. The fresh hot rinse water supply line 40 extends from a source of hot water (to be discussed later) and is connected to the rinse arm 32 and rinse spray heads 36. The wash water supply line 42 is connected to the upper and lower wash arms 34 and 30, and receives wash water from a pump 45 mounted to one side of and exterior of the cabinet. The pump in turn is supplied from an outlet pipe 47 that extends from sump 22 and returns or recirculates the wash water sprayed over the ware in the rack during the wash segment of the machine cycle. The volumetric capacity of sump 22 and outlet pipe 47, along with the height location of the inlet or eye of the impeller in drain pump 45, which is preferably a centrifugal pump with a direct motor drive, mounted in inverted fashion as shown, are important to the features of the invention, and are described in greater detail in connection with later description of the machine operating cycle. Thus, during the wash portion of an operating cycle, pump 45 functions as a recirculating pump means. A solenoid operated drain valve 48 is connected by a branch or drain pipe 49 to the wash water supply line 42 immediately downstream of the outlet of pump 45, and this valve when open allows flow of the pump discharge to a drain line 50 that may be connected into a suitable kitchen drain system 52, according to the applicable code regulations. In many kitchens in newer fast food restaurants the drain system may be considerably above the floor, thus the pumped discharge from the dishwasher is a desired feature in those installations. Also, when the drain valve is open, the path of least resistance to the pump output is through drain valve 48, and flow through the recirculating wash plumbing quickly diminishes due to back pressure created at the nozzles of the wash arms. At this time the pump 45 functions as a drain pump means. During the normal cycle of operations of this machine, as later described, drain valve 48 is opened once each cycle of operation, after the wash segment and before the rinse segment of the cycle. Alternatively as shown in Fig. 3, a solenoid-operated valve 48A, atop a small standpipe 49A in the sump, can be used to gravity drain the chamber to the desired retained volume, and lifting the standpipe can drain the machine at shut down where a floor drain is available and the drain pump means feature is not needed. A solenoid-operated fill valve 55 is connected, in the embodiment shown, to control the supply of fresh water to a booster heater 58, which is a displacement type heater tank having its inlet connected to receive water through fill valve 55, and its outlet connected to the fresh rinse water supply line 40. The booster heater has a heating element with a capacity of (typically) 6kW, and has the usual pressure relief valve 59 which will divert hot water through an overflow pipe in the event the tank pressure exceeds a predetermined value. In the usual case, the booster heater operates at water line pressure, which normally is about 4.219 to 6.328 kg/cm² gauge (60 to 90 psig.) and supplies water at 82°C (180°F) or above in accordance with NSF (National Sanitation Foundation) regulations. The booster heater can be omitted if a source of 82°C (180°F) water is otherwise available, in the case of a high temperature machine, or if lower temperature rinse water is used together with a sanitizing agent, e.g. in a low temperature machine. In those cases the fill valve 55 is simply connected from the supply into the rinse water supply line 40 and the water supply temperature may be of the order of 60°C (140°F). Also, a low capacity (e.g. 500 W) heater may be fitted to sump 22, for example to maintain the wash water at a temperature of at least 71°C (160°F) during recirculation. Such a heater may be, for example, a wire or similar heating strip embodied in an elastomeric pad that can be adhered to the exterior of the sump to heat water in the machine by conduction, if necessary. An optional auxiliary drain valve 48B can also be connected into the bottom of sump 22 to permit total draining of the sump at the end of a period of use, if this feature is desired. However, as will be seen, any water retained in the sump 22 and outlet pipe 47 is essentially fresh rinse water that has been sprayed once over the ware in the machine and then collected. Thus this water, especially in the small retained quantity according to the invention, could be retained for a considerable period without concern. Machine Operating Cycle Referring to Fig. 5, which is a cycle timing chart, an explanation of the operating cycle assumes that the machine has been filled initially, that a loaded rack of soiled ware is in the wash chamber, the drain valve is closed, and the door is closed. An appropriate charge of detergent is added to the water, either manually before the door is closed or automatically when the door is closed and this action is detected. Preferably the control proceeds through a short reset term of a few seconds. Then the pump 45 is started and wash water (detergent added) is recirculated through the wash arms onto the ware, draining back to the sump and to the pump inlet, with pump 45 functioning as a recirculating pump means. This segment of the cycle continues for about fourty-one seconds, then the drain valve 48 is opened and the pump continues to run, discharging wash water to drain. After a period of about seventeen seconds, the pump is stopped. During that time, the pump discharges about 5.678 litres (1.5 gallons) of the wash water before the pump begins to cavitate, and retains 3.028 litres (0.8 gallon). When the drain valve is opened, water pressure to the upper and lower wash arms is reduced, flow through them decreases, and the wash arms and their associated plumbing will drain by gravity to the lowest point, which is the nozzles of the lower wash arm, when the pump stops. In the meantime, pump 45, now functioning as a drain pump means together with the open drain valve, discharges wash water until the level of water in sump 22 and the associated outlet pipe 47 reaches the level of the pump impeller eye, at which time the pump begins to cavitate and effectively ceases to pump water. Thus the 3.028 litres (0.8 gallon) of retained wash water is made up of whatever remains in the outlet pipe and sump at this time, plus whatever drains from the wash water plumbing after the pump stops. A short dwell period of about two seconds follows, after which the fresh water fill valve 55 opens and fresh hot rinse water is supplied to the rinse arm 32 and spray heads 36 under supply pressure. This flow continues for about twenty-two seconds, which is sufficient to thoroughly rinse and sanitize the ware in the case of a high temperature machine. In the case of a low temperature machine, sodium hypochlorite (or other sanitizing agent) may be injected into the flow of rinse water, in known fashion. The amount of fresh rinse water added during this period is 5.678 litres (1.5 gallons). The fill valve is then closed, a dwell period of about three seconds preferably follows during which the rack of ware drains and the fresh water plumbing drains down to the level of the nozzles in the lower rinse arm, and the rack of cleansed ware is unloaded. The sump contains a full charge of 8.706 litres (2.3 gallons), which is retained and has detergent added to it to serve as wash water in the next cycle. The Control System Referring to Fig. 4, which is a wiring diagram for a high temperature machine incorporating the invention, and using a related booster tank 58 as shown in Fig. 1, reference numerals with appropriate suffixes are used to relate the controls to parts of the machine. Thus, the pump motor is identified as 45 M, its control contactor as 45 C, and the contactor coil as 45 CC. The door 15 operates a door switch 15 S which is open when the door is open, closed when the door is closed. The solenoid for the fill valve is 55 S, the drain valve solenoid is 48 S, and the temperature sensor switch for the booster heater is 58 S. The circuit incorporates three relays, the fill control relay FCR, the timer control relay TCR, and a shut down time delay relay TDR which functions to shut down the heaters if the machine has not been run through an operating cycle for a predetermined time. A motor driven cam operated timer T has a drive motor TM and plurality of cam operated switches, later identified, which sequence the machine functions. There is a normally closed pump pressure switch PPS which is physically located (not shown) at the output of pump 45, and a fill cut-off or over-fill switch FCS which has a conventional proximity detector device (for example float operated) that will open switch FCS when the level of water in the bottom of chamber 10 exceeds a predetermined level. The heater element TH is for the low capacity tank heater previously mentioned. A conventional detergent dispenser (not shown), for example in the form of a peristaltic pump device, is actuated by a detergent pump motor DM, and has a normally closed pressure switch DPS connected to its output, so the switch will open if the pump is driven and it feeds a quantity of detergent as required.An audible warning device (e.g. a buzzer) DB can receive power through switch DPS if no detergent output is detected, to warn the operator to refill the detergent dispenser, and a priming control switch DPP for the motor DM is provided, normally spring loaded to the position shown at the top of Fig. 4. A normally open manually operated fill switch MFS is also provided for initially over-riding the timer control of fill valve solenoid 55 S when the machine is first started up. Power is supplied at the service connections which are labeled N and L1. Line L2 is part of a higher voltage supply to the booster heater. A three position manually operated switch ROD (run-off-drain) is provided to initiate machine operation, and it is also indicated on Fig. 1 at the top front of cabinet 10. Switch ROD is shown in its off position; in its run position its common or central contacts ROD-1, which are connected via the fuse to service L1, will be closed on the run contacts ROD-2; the contacts ROD-3 are normally open, but will engage contacts ROD-1 in the drain position of the switch, when it is desired to drain the machine. With the control circuit connected to the service lines, power is available from line L1 to connection FCR-11 of relay FCR through the normally closed contacts 45C-2 of the contactor 45C, and to the normally open contact of switch DPP, to connection TCR -l of the relay TCR and through that relay to its connection TCR-4 and thence to open connection TDR-3 of relay TDR, and also to the common connection of timer switch T-TM. This supplies power to timer motor TM, since it is also connected to the service line N, and the timer advances until its switch T-TM opens and its switch T-RT closes. The operator can at this time have the door open and be loading a rack of soiled ware into the chamber. The relay TCR is energized and transfer its contacts once the door switch l5 S is closed, power going to the coil of relay TCR via the closed door switch and the time delay relay TDR through its connections TDR-8 and TDR-5 to TCR-2. Power is applied to the run indicator or pilot light PL, via TCR-4 and ll. At the same time relay TDR is energized, but its delay period is substantial, for example one hour, so its connections remain as shown. Each time the door switch is opened and again closed, this action resets the relay TDR to begin a new delay period, so relay TDR never transfers until the door switch l5 S remains closed for the time period of the delay relay. Moving switch ROD to its run position closes its contacts ROD-2, and this energizes relays FCR and TCR. Power is supplied to connections FCR-l and 2 of the fill control relay through the run switch contacts ROD-2, time delay relay connections TDR- l and 4, thus relay FCR transfers its contacts upon closing switch ROD to its run position. This supplies power via connections FCR-9 and ll to the tank heat element TH, and via connections FCR-l and 3 to the control for the booster heater in the booster tank. Power is also available at the common connection of timer switch T-RT, via connections TCR-1 and 3, once the temperature sensor switch 58 S is closed, but this will not happen until the water in the booster heater reaches a predetermined high temperature, sufficient to assure 82°C (180°F) rinse water when needed. When the booster tank is ready, power will again be supplied to the timer motor via connections TCR-11 and 9. The timer closes its switch T-FS, and this supplies power to fill valve solenoid 55 S, provided the over-fill control switch FCS is closed. Opening the fill valve allows fresh water to enter the booster heater tank, displacing the hot water into the machine. The timer switch T-PM then closes, energizing the contactor coil 45CC and contactor 45C completes a circuit through its normally open contact 45C-1 to the pump motor 45 M. The pump will run during this portion of the fill period, and when there is sufficient water for the pump to reach its predetermined pressure, the normally closed pressure switch PPS will open, deenergizing the fill valve solenoid 55 S. During this period, the timer switch T-DP closes long enough to energize the detergent pump motor DM, and a dose of detergent is added to the water in the chamber. The pump is now recirculating wash water or liquid through the upper and lower wash arms and back to the sump and the pump inlet. This wash period will continue for approximately sixty-six seconds from the opening of the fill valve. During this interval timer switch T-FS has opened and the timer switch T-DS now opens, energizing the drain valve solenoid 48 S. With drain valve 48 open, pump 45 functions as a drain pump means and the wash water exits through the drain pipe 50. Pressure in the pipes leading to the wash arms drops and flow through them diminishes. As the sump 22 empties, the outlet pipe or conduit 47 begins to pass air to the eye of the pump impeller, it begins to cavitate, and the drain period effectively ceases, although the motor 45 M may still operate for a few seconds. The term of the drain period, i.e. drain valve open, may be of the order of 17 seconds, after which timer switch T-DS opens and the drain valve 48 closes, and the timer switch T-PM opens to stop the pump motor 45 M. Remaining in the chamber is the wash water still in pipe 47, plus whatever water drains by gravity at this time from the wash arms, down to the level of the nozzles in the lower wash arm 30. The volume of this retained wash water can be (as previously explained) of the order of 2.839 to 3.785 litres (0.75 gallons). The cycle proceeds, and timer switch T-RS closes, thus energizing fill valve solenoid 55 S (assuming the draining has proceeded properly and the over-fill switch is still closed). Fresh water again is admitted to the booster heater. At this time the timer switch T-BP closes to shunt the booster heater sensor switch 58 S, lest it should open due to the extended admission of colder water to the booster heater tank. The timer switch T-RS remains closed for a sufficient rinse period, about twenty two seconds, allowing hot rinse water to spray through the rinse system and over the cleansed ware. The rinse water collects in the sump 22 and bottom 20, approximately 5.678 litres (1.5 gallons) along with the retained wash water. When the rinse valve is opened, upon opening of timer switch T-RS, there follows a short dwell period of about three seconds, after which the timer switch T-RT opens, the timer switch T-TM closes, but power to its common connection is not available since relay TCR is still energized and connections TCR 1 and 4 are open. The timer motor stops, and pilot light PL is extinguished, indicating the cycle is complete. The door 15 may then be opened, the rack of clean ware removed, a rack of soiled ware loaded, and the door closed, upon which the cycle will repeat. Opening door switch 15 S deenergizes relays TCR and TDR, thus power is applied through TCR 1 and 12 to timer switch T-TM to reset the timer. If the booster temperature is high enough, opening T-BP will not matter because 58 S will be closed. Should the door remain closed for an extended period, as if the machine is left unattended, or use has stopped and a rack of soiled ware was not loaded, the relay TDR will time out and transfer its contacts. This will open the power supply to the tank heater element TH and also denergize the booster heater control circuit. Fig. 6 shows a modification employing separate pumps for recirculating wash water and for draining (pump out). The sump 22A has a drain tube or pipe 47A leading to a motor driven recirculating pump 45A which merely returns wash water to the wash arms. A separate drain tube 47B also extends from the sump, leading to the inlet of a motor driven drain pump 45B, the outlet of which can be connected to a suitable waste line. In this embodiment, when the wash period nears its end, the pump 45A is stopped, and pump 45B is then run to withdraw wash water from the sump 22A. This continues until the wash water level is lowered to the point where tube 47B enters the sump (a short standpipe connected to tube 47B above the bottom of the sump, can be included if it is desired to retain more wash water). At this time, no more water can be pumped out due to cavitation of the drain pump 45B, but retained wash water remains in the tube 47A leading to pump 45A. This arrangement requires an extra motor driven pump and some extra plumbing, but eliminates the need for a solenoid-operated drain valve, and can be part of an "add on" arrangement for a gravity drain type of machine as described in connection with Fig. 3.

Claims: The method of washing and rinsing consecutive racks of ware in a total cycle time of the order of three minutes or less per rack, comprising the steps of: placing a first rack of ware in an enclosable wash chamber, introducing water into the chamber in a quantity sufficient to enable continuous recirculation of the water by means of a pump at a volume and pressure adequate to strip soil from the ware, introducing a detergent medium into the sump water to produce a wash liquid, recirculating the wash liquid over and onto the ware for a period sufficient to clean the ware, discontinuing wash liquid circulation and draining a first portion of soiled wash liquid while retaining a second portion of the wash liquid for use as wash liquid in the next cycle for washing a different rack of ware, rinsing the washed ware with a pressurized rinse spray from a rinse system connected and dedicated to a fresh water supply and collecting the rinse water with the retained wash liquid, the volume of rinse water and duration of rinsing being essentially a minimum sufficient to perform effective rinsing, removing the rack of rinsed ware from the chamber and replacing it with a rack of soiled ware, and repeating the foregoing steps using as wash liquid the combined retained wash liquid and fresh rinse water. A method according to claim 1 wherein draining is accomplished by pumping the first portion of wash liquid to a waste line located at a level above the pump. A method according to claim 2 wherein recirculating and draining are accomplished by a common pump means. A method according to claim 1 wherein draining results from opening a drain valve to permit the chamber to drain by gravity. A method according to claim 4 wherein the drain valve is above the bottom of a sump located in a bottom wall of the chamber to inhibit draining of the retained portion. A method according to any preceding claim wherein said retained portion of wash liquid comprises at least 25% of the wash liquid used for recirculation during washing. A warewasher for use in commercial establishments by using a single batch of water for washing and rinsing a rack of dishes and operating on a cycle time of the order of a few minutes or less, comprising a cabinet including means defining a wash chamber (10), a door (15) for opening and closing said chamber for introduction of racks of soiled ware into the chamber and removal therefrom upon completion of washing and rinsing, a sump (22) at the bottom of the chamber for holding water for use as a supply in washing the ware, recirculating pump means (45) having an inlet connected to said sump, at least one wash arm (30) within said chamber and having a plurality of wash nozzles, said wash arm being in fluid connection with said recirculating pump means whereby,during operation of said pump means,said wash arm provides pressurized spraying of water from the sump onto the ware in the rack, a plurality of rinse nozzles (32, 36) in said chamber located both above and below the position occupied by a rack (25)of ware when introduced into the chamber and,in operation, being in fluid communication with a supply of fresh water under pressure outside said chamber, valve means (55) intermediate said water supply and said rinse nozzles for enabling rinsing of washed ware in response of opening of said valve means, drain pump means (45) having a water drain inlet (47) and a water drain outlet (49), a drain line (50) for connecting said drain outlet to a waste line (52), the drain inlet being in fluid communication with the bottom of the sump, a normally-closed valve means (48) intermediate said waste line and said sump, and control means (Figs. 4A & 4B) for operating said recirculating pump means to first recirculate wash water onto the ware for washing the ware and thereupon discontinuing operation of the recirculating pump means, for next operating the drain pump means to remove wash water from the sump and, after discontinuing draining, opening the valve means in the fresh water supply to rinse ware through said rinse nozzles and closing said valve means upon rinsing the ware to complete the cycle for a given rack of ware, characterised by: said recirculating pump means, draining pump means, wash arms and rinse nozzles being located at levels relative to the sump whereby, upon completion of draining, a predetermined quantity of wash water is retained in said sump for mixing with rinse water subsequently issuing from the rinse nozzles to provide a combined quantity of water in said sump for washing a subsequent rack of ware upon removal of the clean rack of ware from the chamber, thereby enabling usage of a quantity of water for rinsing each rack of ware which is adequate to provide satisfactory rinsing while enabling the volume of rinse water for each rack to be maintained essentially at a minimum to conserve energy and water. A warewasher as defined in claim 7 wherein the pump means (45) is supported to one side of and exterior the cabinet and includes a centrifugal impeller having its inlet slightly above the bottom of said sump (22) whereby the pump will cease effective output before the sump and its outlet pipe (47) are emptied. A warewasher as defined in claim 7 wherein said recirculating pump means and said drain pump means comprise a single pump (45) with a single impeller. A warewasher as defined in claim 7 wherein said recirculating pump means (45A) and said drain pump means (45B) are separate pumps. A warewasher as defined in claim 7 wherein said drain means includes drain pump means (45) discharging to a waste line (52) located at a level higher than said sump. A warewasher for use in commercial establishments by using a single batch of water for washing and rinsing a rack of dishes and operating on a cycle time of the order of a few minutes or less, comprising a cabinet including means defining a wash chamber (10), a door (15) for opening and closing said chamber for introduction of racks of soiled ware into the chamber and removal therefrom upon completion of washing and rinsing, a sump (22) at the bottom of the chamber for holding water for use as a supply in washing the ware, recirculating pump means (45) having an inlet connected to said sump, at least one wash arm (30) within said chamber and having a plurality of wash nozzles, said wash arm being in fluid connection with said recirculating pump means whereby, during operation of said pump means, said wash arm provides pressurized spraying of water from the sump onto the ware in the rack, a plurality of rinse nozzles (32, 26) in said chamber located both above and below the position occupied by a rack (25) of ware when introduced into the chamber and, in operation, being in fluid communication with a supply of fresh water under pressure outside said chamber, valve means (55) intermediate said water supply and said rinse nozzles for enabling rinsing of washed ware in response of opening said valve means, drain means (48A, 49A) in fluid communication with the sump, and including a normally-closed drain valve means (48A), and control means for operating said recirculating pump means to first recirculate wash water onto the ware for washing the ware and thereupon discontinuing operation of the recirculating pump means, for next operating the drain means to remove wash water from the sump and, after discontinuing draining, opening the valve means in the fresh water supply to rinse ware through said rinse nozzles and closing said valve means upon rinsing the ware to complete the cycle for a given rack of ware, characterised by: said drain means being operable to enable gravity draining of the sump to a predetermined level when the drain valve means (48A) is open, whilst achieving controlled retention of wash water, whereby, upon completion of draining, a predetermined quantity of wash water is retained in said sump for mixing with rinse water subsequently issuing from the rinse nozzles to provide a combined quantity of water in said sump for washing a subsequent rack of ware upon removal of the clean rack of ware from the chamber. A warewasher as defined in claim 12 wherein the inlet to said drain valve means (48A) is located above the sump bottom, to inhibit draining of the retained quantity of wash water. A warewasher as defined in any of claims 7 to 13, wherein the supply of water used for rinsing is maintained at a temperature of approximately 82°C (180°F), and wherein a heater (TH) is provided for maintaining wash water at a temperature of at least 71°C (160°F) during recirculation.

Inventors: NOREN, TORE H. C/O THE STERO COMPANY
Applicants: THE STERO COMPANY
Application year: 1987
Main classification: A47L15
IPC codes: A47L15