Abstract:
A high pressure pump ( 14 ) supplies cleaning fluid from a reservoir ( 12 ) to spray nozzles ( 20 ) inside a washing chamber ( 10 ). The spray nozzles ( 20 ) spray the cleaning fluid over a load to be cleaned. Used cleaning fluid is collected in a sump ( 30 ). A sump pump ( 32 ) drains the sump. The combination of the high pressure pump and sump pump provides more efficient cleaning of the load and eliminates the requirement for a deep sump beneath the washer. A vertical traveler ( 22 ), having a pair of counterbalanced spray arms ( 24 ), raises and lowers the spray nozzles counter cyclically; a detergent injection system ( 50 ) accurately meters a correct amount of detergent is added to the cleaning fluid; and a filtration device ( 34 ) filters suspended material from the used cleaning fluid and uses a portion of the cleaning fluid to clean itself.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to the cleaning and disinfecting arts. It finds particular application in conjunction with the cleaning of animal cages and racks and also healthcare and scientific equipment, such as hospital beds, wheelchairs, utensils, carts and instrument containers, and will be described with particular reference thereto. It should be appreciated, however, that the invention is also applicable to the cleaning and disinfecting of other pieces of equipment, particularly those which have been in contact with biological wastes. 
     Items such as animal cages and associated racks and large pieces of healthcare and scientific equipment are generally cleaned at frequent intervals to remove biological waste, such as urine, feces, and uneaten food. Thorough cleaning aids in preventing the spread of disease and reduces the development of unpleasant odors. Washers have been developed to handle the large scale cleaning and disinfecting of animal such items. Typically, these are large enough for a load to be processed to be wheeled manually into the washer. Cleaning fluid is then sprayed through jets onto the load. The used fluid is collected in a pit or sump, below the washer. The fluid is either recycled or discarded, depending on the degree of contamination. 
     When large numbers of items are to be cleaned, the cycle time of the machine is an important factor. A washer for items such as cages is necessarily a large and invariably a costly investment, and it is thus desirable for a facility to clean all such items in a single washer. Typically, the jets which are used to spray cleaning fluid over the load operate at around 20 p.s.i. (1.4 bar). Stripping the often dried and adherent biological matter from the load with fluid at this pressure is time consuming and cleaning cycle times of 40 minutes or longer are common. In addition, low pressure washing uses large quantities of cleaning fluid to compensate for the low level of impingement of the sprays upon the process load. 
     The length and effectiveness of the cleaning system are also dependent on the arrangement of the jets within the washer. Cages and racks and scientific and healthcare equipment and racks are often large, with components which inhibit movement of the cleaning fluid, resulting in incomplete cleaning of the load. A number of systems have developed for directing the sprays of cleaning fluid so as to improve coverage of the load. In one system, a rotary spray arm is used. The pressure of the cleaning fluid causes the arm to rotate. Holes in the spray arm spray the fluid into the washer. The effectiveness of cleaning, however, is reduced because the sprays emitted tend to fight against each other, reducing the power of the sprays and varying their direction. Some of the energy of the spray is utilized in rotating the spray arm, reducing the water pressure efficiency of the spray. It is also difficult to ensure coverage of the entire load with a rotating spray arm. Further, the soil washed from the load tends to be pushed toward the center of the washer, collecting on parts of the load, rather than dripping off the load and into the sump. 
     In another cleaning system, a tube supplies cleaning fluid to two spray bars or arms, movably mounted on either side of the washing chamber. The bars move simultaneously up the side of the washer, spraying fluid from nozzles as they travel. The sprays provide coverage of the entire washer, and increase cleaning efficiency through the effect of fluid dripping through the load. The system generally includes a complicated movement mechanism. A safety clutch is therefore provided to reduce the danger to workers in the event that the mechanism fails to operate properly. The sprays from the two spray bars tend to fight against each other. In a similar cleaning system, spray arms travel horizontally, rather than vertically. In addition to having some of the problems associated with the vertical cleaning system, the sprays tend to push the soil into the center of the load, resulting in less efficient cleaning. 
     There remains a need for a cleaning system with a reduced cycle time that strips the biological matter from the load and sanitizes the load more effectively. 
     Effective cleaning of the load is also achieved by maintaining the concentration of a selected detergent in the cleaning fluid. Because of the often high cost of the detergent, and the large quantities of cleaning fluid employed, it is desirable to maintain the detergent concentration close to the minimum level required to insure effective cleaning. Traditionally, the cleaning fluids are pumped in solution from storage tanks. Periodically, the fluid in the tank is replenished by the separate addition of detergent, in concentrated form, and water. 
     Measuring the actual concentration of the detergent in the tank is time consuming, therefore methods have developed which determine the concentration indirectly. Typically, one of two methods is used to estimate the concentration of detergent. In the first method, the addition of detergent to the tank from a detergent supply container is timed. The concentration of detergent is inferred from the operating time of a pump used to transfer the detergent. This provides a simple means of determining detergent concentration. However, if there is little or no detergent passing through the pump, which could occur, for example, if the pump is not working properly, then inaccurate measurements of detergent concentrations are obtained. Inadequate cleaning and sanitization of the process load results when the detergent concentration drops below a minimum level. 
     In the second method, the detergent concentration is inferred from a measure of the pH or conductivity of the cleaning solution. This correlates well with the detergent concentration in the fresh cleaning fluid. It is usual, however, to recycle a portion of the cleaning fluid from the washer into the tank for reuse. The recycled cleaning fluid contains soil from the load which influences the pH and conductivity of the cleaning fluid. Thus, the measure of pH or conductivity gives an inaccurate determination of the concentration of detergent in the tank, the inaccuracy becoming more pronounced at higher soil concentrations. There remains a need for a cleaning system that insures effective cleaning by providing a more accurate method of monitoring the rate of addition of detergent. 
     The cleaning fluid is generally retained in the sump. The cleaning fluid is pumped from the sump by a sump pump and circulated to the nozzles in the washing chamber. The fluid level in the sump must remain deep enough that the sump pump does not cavitate. Conventionally, cage and rack washers employ sumps of around 30-40 cm deep to supply the necessary depth of fluid for operation of a typical sump pump. To provide this depth, a large well is usually constructed through the floor beneath the washer, with suitable reinforcement for the washer. Constructing such a well within a concrete floor is frequently expensive and time consuming. In some floor structures, there is insufficient below ground depth available for the sump and the load is raised well above floor level to enter the washer. Ramps provide a means of raising the load, but as cages and hospital and scientific equipment are frequently heavy, it is difficult to push them up a ramp that is too steep. Shallow ramps make loading the washer easier but take up considerable space and are hazardous if wheeled carts are left unattended and accelerate down the slope. 
     Typically, a portion of the cleaning fluid is returned to the tanks for recycling after it has been used in the washer. Generally, sump pumps do not begin to operate until a sufficient head of fluid has collected in the sump. Thus, there is a delay between cycles while a portion of the used cleaning solution is discarded and replaced with fresh water and added detergent. In addition, because of the different soils encountered, cleaning systems typically include two or more cycles, each using a different cleaning fluid. Separate tanks are used for each of the cleaning fluids. To avoid mixing of the different fluids, the contents of the sump are pumped to the tanks between cycles. There is a considerable time lag between cycles as the pump completes the removal of the collected fluid from the sump. Moreover, the pump ceases to operate once the fluid drops below the cavitation level and the remaining fluid is simply drained to the waste system. Draining of the sump in this way takes considerable time, and also increases operating costs through higher detergent use and costs of treating the waste to meet environmental standards. 
     The fluid collecting in the sump is typically heated by a steam coil, located in the sump, to maintain the temperature of the fluid during cycles. Because of heat losses from the sump compounded by the length of time spent by fluid in the sump, considerable wastage of energy occurs. In addition, the fluid in the sump is heated to a higher temperature than that employed in the washer to compensate for cooling. The hot soil-contaminated cleaning fluid and steam coil pose a danger to workers entering the washer between cycles, if they should accidentally fall into the sump. There exists a need for a cage washer that operates without a deep sump and that allows rapid removal of the used cleaning fluids from the sump. There also exists a need for a cleaning system which minimizes heat losses from the cleaning fluid. 
     Because of the cost of detergents, it is beneficial to reuse as much of the cleaning fluid as possible. Traditionally, a filter system removes solid matter from the used cleaning fluid before the fluid is returned to the fluid tank which filter becomes clogged with the solid material. The solid material clogging the filter reduces the wash pressure and efficiency of cleaning. Periodic down-time for manual cleaning of the filter is, therefore, encountered. This filter cleaning time limits the operating period of the washer, reducing the number of loads processed in a given time. There is a need for a filter system which operates continuously, flushing the build up of solid material from the filter without the need for frequent cleaning of the filter. 
     The present invention provides a new and improved washer with an improved cleaning system which overcomes the above referenced problems and others. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, a washer is provided. The washer includes a washing chamber, with spray nozzles disposed in the washing chamber for spraying a cleaning fluid over a load to be cleaned. A sump at the bottom of the washing chamber collects the cleaning fluid sprayed over the load. A sump pump removes cleaning fluid from the sump. A high pressure pump pumps cleaning fluid from a cleaning fluid reservoir to the spray nozzles. 
     In accordance with another aspect of the present invention, a washer is provided. Spray nozzles disposed within a washing chamber spray a cleaning fluid into the chamber. A pump pumps cleaning fluid to the spray nozzles from a cleaning fluid reservoir. A vertical traveler includes first and second counterbalanced spray arms, disposed adjacent opposite sides of the washing chamber, the spray nozzles disposed on the spray arms. The traveler also includes a mechanism which supports the spray arms for vertical travel and a drive system which alternately raises and lowers the spray arms, the first spray arm traveling in an opposite vertical direction to the second spray arm. 
     In accordance with yet another aspect of the present invention a washer is provided. Spray nozzles disposed in a washing chamber spray a cleaning fluid over a load to be cleaned. A pump which pumps cleaning fluid from a cleaning fluid reservoir to the spray nozzles. A filtration device removes suspended material from the cleaning fluid. The device includes a fluid inlet which receives cleaning fluid and a first fluid outlet which directs unfiltered cleaning fluid from the filtration device to a drain. The device also includes a valve which selectively closes to prevent cleaning fluid from exiting the filtration device through the first fluid outlet. The device further includes a filtration screen which filters suspended material from the cleaning fluid and a second fluid outlet through which filtered cleaning fluid leaves the device. 
     In accordance with another aspect of the present invention a fluid injection system for insuring accurate delivery of a preselected quantity of a fluid is provided. A peristaltic pump delivers the fluid, the preselected quantity of fluid measured in terms of a number of pulses of fluid delivered by the pump. A flow meter indicates whether fluid is flowing through the pump, the flow meter detecting a flow of fluid in the fluid injection system. 
     In accordance with another aspect of the present invention, a method for cleaning large equipment is provided. The method includes supplying spray nozzles with a cleaning fluid at a high pressure and spraying the cleaning fluid from the spray nozzles over a load of equipment. The method further includes collecting sprayed cleaning fluid in a sump and draining the cleaning fluid from the sump with a sump pump. 
     In accordance with another aspect of the present invention, a cleaning system is provided. The system includes supplying spray nozzles with a cleaning fluid and spraying the cleaning fluid from the spray nozzles over a load to be cleaned. The method also includes sequentially raising and lowering the spray nozzles with a vertical traveler. The sequence includes raising a first set of the spray nozzles at the same time as lowering a second set of the spray nozzles. The sequence further includes lowering the first set of the spray nozzles at the same time as raising the second set of the spray nozzles. 
     In accordance with another aspect of the present invention, a cleaning system is provided. The system includes supplying spray nozzles with a cleaning fluid at a high pressure, spraying the cleaning fluid from the spray nozzles over a load to be cleaned and collecting sprayed cleaning fluid. The system also includes closing a filtration valve connected to a first outlet on a filtration device and passing the sprayed cleaning fluid into the filtration device. The system further includes filtering suspended material from the sprayed cleaning fluid and passing the filtered cleaning fluid from the filtration device through a second outlet. Still further, the method includes selectively opening the filtration valve and allowing a portion of the sprayed fluid to pass through the first outlet and through the open filtration valve to remove suspended material trapped within the filtration device. 
     One advantage of the present invention is that the cycle time for the washer is considerably reduced over conventional systems. 
     Another advantage of the present invention is that it enables optimal detergent concentrations to be maintained with minimal detergent additions. 
     Yet another advantage of the present invention resides in its effective cleaning, with lower volumes of cleaning fluid. 
     Still further advantages reside in the shallow depth of the sump, simple installation, and the low volume of cleaning fluid remaining therein between cycles. 
     Still further advantages of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating a preferred embodiment and are not to be construed as limiting the invention. 
     FIG. 1 is a schematic of a preferred embodiment of a cleaning system for a washer according to the present invention; 
     FIG. 2 illustrates an expanded, perspective illustration of the vertical traveler of FIG. 1; 
     FIG. 3 is a schematic of a detergent supply system in accordance with the present invention; 
     FIG. 4 is an expanded side view of the vertical filtration device of FIG. 1; and 
     FIG. 5 a schematic side sectional view of the vertical filtration device of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to FIG. 1, a load to be cleaned is wheeled into a washer  1 , which includes a washing chamber  10 , and washer doors (not shown) are closed. A source of cleaning fluid, such as a cleaning fluid reservoir or tank  12 , supplies cleaning fluid to a pump, preferably a high pressure pump  14 , through a fluid line  16 . Optionally, plurality of tanks  12 A,  12 B and  12 C each carry a different cleaning or rinse solution. Valves  18 A,  18 B and  18 C are connected to cleaning fluid tanks  12 A,  12 B and  12 C, respectively, for selectively delivering cleaning fluid to the fluid line  16 . The high pressure pump  14  pumps the cleaning fluid at a pressure of between 5 and 15 bar, preferably around 7 to 9 bar, to spray nozzles  20  in the washer chamber. 
     With continuing reference to FIG.  1  and further reference to FIG. 2, a vertical spray traveler  22  supports spray arms or bars  24 , disposed inside the washing chamber  10 , each spray arm carrying a number of the spray nozzles  20 . The high pressure pump  14  supplies the spray nozzles with cleaning fluid. An in-line temperature booster or heater  26  raises the temperature of the cleaning fluid to a preselected washing temperature before the fluid reaches the spray nozzles. The spray nozzles spray the cleaning fluid over the load to be cleaned. Depending on the nature of the load to be cleaned, several wash cycles are employed. A typical cleaning process includes a pre-wash, first detergent wash, mid-rinse, second detergent wash and final rinses. The load is then dried in the conventional manner. 
     A shallow sump  30  is located beneath the washing chamber  10  and collects the used fluid as it drips down from the washing chamber. A sump pump  32 , preferably a self-priming pump, sits in the sump. The sump pump directs the used cleaning fluid to a vertical filtration device, or filter  34  and the tanks  12  or to a drain  36 . Depending on the level of soil in the used fluid, the fluid is either reused or disposed of. If the fluid is to be reused, used fluid from the vertical filtration device is directed to the fluid tank. If the fluid is to be disposed, the fluid is directed to the drain. Fluid directed to the drain flushes solids from the vertical filtration device. 
     Preferably, before disposal, the fluid passes through a cool down vessel  40  where the temperature and pH of the fluid are adjusted to meet environmental standards. Preferably, a pH probe  42  monitors the pH of the used fluid in the vessel. The pH of the fluid is adjusted to the regulatory standard by the addition of acid or alkali, as required. 
     With continuing reference to FIG.  1  and further reference to FIG. 3, a detergent flow metering system  50  periodically supplies fresh concentrated cleaning fluid to the tanks  12  to maintain cleaning fluid levels. A water inlet  52  supplies water to tanks  12  to dilute the incoming concentrated fluid. Preferably the water entering through inlet  52  is hot water. This raises the overall temperature of the cleaning fluid in the tanks and allows the in-line heater  26  to bring the temperature of the cleaning fluid rapidly up to the required wash temperature. 
     The lower pressure sump pump  32  and the higher pressure pump  14  provide both a high pressure wash and also allow for the sump  30  to be small. The high pressure pump provides high pressure cleaning fluid to the nozzles  20 , relieving the sump pump of the task of pressurizing the fluid in the system. In the preferred embodiment, the sump pump transfers fluid from the sump to the tanks  12  or to the drain  36 . A small sump pump is adequate for this task. The depth of the sump is reduced by using a self priming sump pump  32  which operates at the low fluid levels. A sump  30  of around 10-12 cm provides an adequate fluid depth for the self priming pump. 
     A washing system with a shallow sump offers a number of advantages over conventional systems. First, construction costs are reduced because the size of the area to be excavated is much smaller, and the extent of support is much less. Alternatively, the pit can be eliminated altogether by constructing the sump above ground. Long, shallow ramps (not shown) between floor level and the floor level of the washing chamber  10  readily allow heavy loads to be wheeled into and out of the washing chamber  10 . 
     Further advantages of the shallow sump  30  arise because cleaning fluid does not accumulate in the sump. The sump pump  32  is designed to operate at low fluid levels and, in the preferred embodiment, operates fairly continuously to remove fluid as it drains into the sump from the washing chamber  10 . This reduces the cycle time of the washer  1  because there is little fluid in the sump to be removed between cycles. A cycle time of around 15 minutes is preferably achieved. In addition, because it operates at lower fluid levels than a conventional washer sump pump, the sump pump is able to remove virtually all the fluid in the sump. This reduces the amount of cleaning fluid which is wasted, cutting the costs of detergent, water and environmental compliance in operating the washer. 
     Preferably the sump  30  has a sloping floor  54  which further reduces the quantity of fluid in the sump. 
     The shallow sump  30  and in-line temperature booster  26  cooperate to provide further advantages of the washer. Conventional washers which use a steam coil located within the sump, have high heat losses. In the preferred embodiment of the present invention, the shallow sump does not hold fluid for long periods. The sump pump  32  rapidly returns the cleaning fluid to the cleaning fluid tanks  12 , which are preferably insulated to reduce heat loss, or directs the fluid to the drain  36 . Thus, heat loss from the sump is minimized. This allows the steam coil to be eliminated. The in-line temperature booster heats the fluid more efficiently than would a sump steam coil by heating the cleaning fluid just prior to its entry into the washing chamber  10 . 
     The high pressure pump  14  and vertical traveler  22  combine to provide an efficient system of cleaning cages and racks and other scientific and healthcare equipment by reducing the length of the cleaning cycle and reducing the volume of cleaning fluid circulating through the washing chamber  10  in the cycle. The high pressure pump, preferably constructed of a high grade stainless steel, supplies cleaning fluid at a pressure at least three to five times higher than in conventional cage cleaning systems. A pressure of around 7-9 bar at the nozzles (around 9-10 bar at the pump) is readily achieved in the preferred embodiment. Fluid at this pressure removes soil from the load to be cleaned more effectively than in conventional washers, thereby reducing the length of the cleaning cycle. The range of the spray from each of the nozzles  20  is also increased, improving the cleaning efficacy of less accessible portions of the load. 
     Varying the shape and number of the nozzles  20  on each spray arm  24  also influences the impact of the spray. In the preferred embodiment, 32 V-shaped nozzles provide good impingement and cleaning efficiency, although it is envisaged that the number and shape of the nozzles could be adjusted, dependent on the nature of the load and the pumping equipment used. 
     In the preferred embodiment, the flow rate is reduced to around 250 l/min, as compared with 740 l/min in a conventional system. Even at the reduced flow rate, the wash impingement is considerably higher than in conventional systems, because of the higher pressures used. Approximately 200% higher impingement is generated, at a distance of 30 cm from the nozzles, for the combination of flow rate, pressure, and nozzle dimensions recited. A reduced flow rate allows for smaller equipment. Tubes, valves and pumps are all smaller than in conventional high flow systems. The reduced flow rate also cuts operating costs in terms of energy use by pumps and heaters, detergent quantities, water consumption and fluid disposal. 
     With particular reference to FIG. 2, the alternating vertical traveler  22  includes two counterbalanced spray arms  24 ,  24 ′ one disposed on either side of the washing chamber  10 . Like parts associated with the two spray arms are similarly followed by a prime (′). The spray arms move up and down in opposite directions; as the first spray arm  24  moves downward, the second spray arm  24 ′ moves upward. Nozzles  20 , optionally holes formed in the spray arms, spray cleaning solution generally toward the center of the washing chamber. Thus, as the first spray arm is spraying the portion of the load closest to the top of the washing chamber, the second spray arm is simultaneously spraying the bottom of the load, close to the floor level. Cleaning fluid also flows down from the top of the load and additional nozzles (not shown) on the top of the washing chamber, aiding in the cleaning of lower portions, which typically include the heaviest soiled areas of cages. As the spray arms move toward the mid point of their travel, the sprays of cleaning fluid cross. For all but the crossing point, the spray arms spray independently, impinging on separate portions of the load. The load is first sprayed from one side and then the other. Therefore, the efficiency of the spray system is maximized and thorough cleaning of the entire load is achieved rapidly. 
     The traveler  22  preferably includes a drive system  60  for vertical countercyclical movement of the spray arms  24  and  24 ′, and a mechanism  62  for supporting the spray arms  24  in such a way that the travel of each spray arm is limited to vertical movement in a plane approximately parallel to sides of the washing chamber  10 . It is to be understood, however, that the invention is not limited to the drive system and mechanism described herein, but that other means conventionally known in the art for alternatively raising and lowering the two spray arms are also contemplated. 
     The mechanism  62  preferably includes a pair of followers  64  and  64 ′ each of which holds one of the spray arms  24  so that it extends approximately horizontally on either side. Specifically, the two followers are slidably mounted in a pair of vertical tracks or rods  66  and  66 ′ with the spray arms situated toward the center of the washing chamber  10 . 
     Spray arms  24  include hose attachments  68 . Flexible U-shaped hoses (not shown), connect to the hose attachments to supply cleaning fluid. The U-shaped hoses are fed from supply line  16 . The spray arms and mechanism  62  are preferably constructed of materials that withstand the chemical cleaning environment and high-temperature drying commonly used. 
     In the preferred embodiment, the drive system  60  includes a drive cable or belt  70  connected with both followers  64 . A drive means  72 , such as a rodless pneumatic cylinder or alternating chain and sprocket system, engages the drive cable. The drive means is preferably housed outside the washing chamber  10 , or is isolated from the sprays of cleaning fluid, so that it is not subject to damage by the cleaning fluids used in the washer  1 . 
     The drive cable  70  forms a closed loop which passes from the drive means  72  to the first follower  64  and then to the second follower  64 ′ before returning to the drive means. A guide system, such as a series of pulley wheels  74 , positions the drive cable  62  so that the drive cable does not interfere with the operation of the spray arms  24  or the load to be processed. The drive means  72  draws the drive cable  70  a preselected distance in one direction then allows the drive cable to return, or draws the drive cable, the same distance in the reverse direction. In this way, the spray arms are moved simultaneously, one traveling upward, while the other travels downward. Because the spray arms and followers are counterbalanced, there is little tension on the drive means  72 . The life expectancy of the drive means is much longer than in a conventional spray system. In addition, it is easier to detect jams and obstructions in the washing chamber  10  than for a conventional system because any impediment to movement of the spray arms is detected by the drive system and the movement of the spray arms is arrested. Alternatively, a break away system  75  releases the cable from the mechanism  62  or from the drive means. As an additional safety precaution, the mechanism is sized and configured so as to be easily grasped by an operator within the washing chamber without damage to the operators hand. By pulling on one of the spray arms, the movement of the drive cable  70  is arrested. This safety feature eliminates the need for a safety clutch, as commonly used in moving mechanical spray systems. Optionally, the speed of the drive means is variable, causing the spray arms to travel up and down at a preselected rate. 
     Preferably, a security cable  76  links the followers  64  and  64 ′. The security cable protects workers operating inside the washing chamber  10  by preventing the followers and attached spray arms  24  from falling in the event of a malfunction of the drive system  60 . As an additional safety feature, a safety cover  78  covers at least part of the drive cable  70  to protect workers from injury by the cable. 
     With reference to FIGS. 1 and 3, the detergent injection system  50  regulates the amount of detergent or other cleaning or rinsing fluid introduced to the cleaning fluid tanks  12 , insuring that the preselected amount has been added. In a typical cycle, the cleaning fluid is replenished at intervals by discarding a certain portion of the cleaning fluid that has circulated through the washing chamber  10 , and refilling the cleaning fluid tank with fresh detergent. The proportion of the cleaning fluid to be discarded is determined by evaluations of the level of soil on the load to be processed. Typically, for lightly soiled loads, such as rodent cages, about 10% of the cleaning fluid is discarded after each load, while for heavily soiled loads, such as primate cages, a much larger proportion is discarded, up to 100%, typically, for the most heavily soiled loads. After a preselected number of cleaning cycles, the contents of the tanks  12  are completely drained and refilled with fresh cleaning fluid. In this way, effective cleaning of the process load is obtained, and detergent costs are minimized. 
     The detergent injection system  50  includes flow meter  80  and a metering pump, such as a peristaltic pump  82 , for each cleaning fluid tank  12 . A supply of detergent, such as supply containers  84 , supplies detergent, or other selected cleaning fluids, to the cleaning fluid tanks for replenishing the tanks. The peristaltic pump pumps the detergent from the supply container to the cleaning fluid tank. In the embodiment shown in FIG. 3, three supply containers,  84 A, B and C, contain an alkaline detergent, a rinse aid, and an acid detergent, respectively. The three supply containers supply corresponding cleaning fluid tanks  12 A, B and C, respectively, although it is envisaged that combinations of detergent could be supplied to a single tank. 
     Detergent is metered into the cleaning fluid tank  12  by peristaltic pump  82 . As the peristaltic pump rotates it delivers predetermined volume pulses of detergent into the cleaning fluid tank. The amount of detergent added is proportional to the number of these detergent pulses. Although a peristaltic pump  82  is the preferred means of delivering detergent, alternatively, a conventional pump supplies detergent to the tank, the detergent addition measured in terms of the operating time of the pump. 
     Where the detergent is added to the tank  12  in concentrated form, water is also added to the tank through inlet line  52  to dilute the detergent to the desired concentration within the tank. A series of valves  86 A, B and C optionally allow for the separate addition to tanks  12 A, B, and C respectively. 
     With continuing reference to FIGS. 1 and 3 and further reference to FIG. 4 a control circuit  88  optionally regulates the amount of detergent and the volume of water added to the tank  12  to replenish the cleaning fluid. A water flow meter  90  detects the volume of water entering the tank. The control circuit monitors the volume of water and addresses a look-up table  92 . The look-up table determines the amount of detergent to be added. The control circuit signals the peristaltic pump  82  to deliver a corresponding number of detergent pulses. The amount to be added is dependent on such factors as the type of washing cycle, the type and concentration of the detergent, the level of soil on the load, and the proportion of cleaning fluid reused. 
     The flow meter  80  acts as a check on the injection system  50  by indicating whether fluid is flowing into the tank  12 . This insures that the detergent is being delivered to the tank  12 . In the event that the detergent in the container  84  is consumed, or blockages occur in the system, the flow meter  80  registers this as a decrease in the measured flow or an absence of flow. Optionally the flowmeter  80  is linked to an alarm system  94  which alerts the operator to the insufficiency in the detergent flow. 
     Optionally, the alkaline and acid detergents in the supply containers  84 A and C are used to balance the pH of the waste fluid in the cool-down vessel  40 . Cool down supply lines  96 A and B carry the detergent to the cool-down vessel  40 . Acid and alkaline neutralizer pumps  98 A and  98 B, respectively, control the flow of detergent to the cool-down vessel  40 . 
     With reference to FIGS. 1 and 5, the self cleaning filter or vertical filtration device  34  filters used cleaning fluid for reuse. The filter  34  reduces down-time of the washer by periodic self cleaning of the filter during portions of the cleaning cycle when the filter is not being employed for filtering the used cleaning fluid collected in the sump  30 . In a typical cleaning cycle, the sump pump  32  delivers the used fluid to the self cleaning filter through a used fluid line  100 . The used fluid is recycled by passing the fluid through the filter  34  and returning the filtered cleaning fluid to the tank  12 . To maintain cleaning efficiency, however, a portion of the used fluid is discarded, to be replaced by fresh cleaning fluid. The fluid to be discarded is used to clean the filter of suspended material such as soil and dirt that collects in the filter during filtration of the cleaning fluid. A filtration valve  102  selectively opens to direct fluid from the filter  34  through a spent fluid line  104  to the drain  36 . The filter  34  is cleaned automatically by the portion of the used cleaning fluid that is directed through the filter to the drain  36 . 
     The filter  34  includes a filtration chamber  106  and a filtration screen  108 , disposed within the filtration chamber. The filtration chamber includes a fluid inlet  110 , a lower or first fluid outlet  112 , and second, or side fluid outlet  114 . The filtration screen  108  preferably defines a cylinder. First and second annular gaskets, such as upper gasket  116  and lower gasket  118 , respectively, seal the cylindrical screen  108  at its open ends around upper inlet  110  and lower outlet  112 . The filtration screen thereby surrounds a central region  120  of the filtration chamber. 
     Used cleaning fluid enters the central region  120  of the filtration chamber  106  through upper inlet  110 . When the filtration valve  102  is closed, the cleaning fluid passes through the screen  108 . The screen preferably comprises a mesh, such as a stainless steel mesh, the mesh size selected to trap soil and other suspended particles within the central region, while not unduly limiting the flow rate of the cleaning fluid through the filter  34 . The filtered used cleaning fluid exits the filtration chamber  106  through side outlet  114 . A recycled fluid line  122  is connected to the side outlet. The recycled fluid line returns the filtered cleaning fluid to the cleaning fluid tank  12 . 
     When the filtration valve  102  is open, the majority of the cleaning fluid passes straight through the central region  120  of the filtration chamber  106 . As it does so, it collects soil and other dirt trapped by the screen  108 , leaving the screen and central region free of accumulated soil and other particulates and ready to filter subsequent additions of cleaning fluid when the filtration valve is again closed. 
     Cleaning the filter  34  in this way reduces operating costs by using waste cleaning fluid rather than fresh water to remove accumulated particles from the filter. Further, by cleaning the filter during the cycle, considerable time is saved because the operation of the washer  1  is not halted to allow for separate cleaning. 
     The invention has been described with reference to the preferred embodiment. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.