Apparatus for filtering and heating a liquid
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to liquid handling systems, and, more particularly, to such systems requiring both filtering and heating of a liquid. 
     2. Description of the Prior Art 
     It is known in the prior art that the efficacy of liquids used in processing systems, such as photographic processing systems, can be extended if the liquids are filtered either continuously or periodically. Also, it is often necessary to control the temperature of liquids used in such processing systems. In one type of liquid handling system known to the prior art, a processing liquid is pumped from an applicator assembly, used in a photographic processing apparatus, through a housing containing a filter to a separate housing containing a heater. The heated and filtered liquid is then returned to the applicator assembly. Difficulties encountered using systems of the aforementioned type include excessive pressure drop, possible leakage of liquid at the numerous fittings required and increased space requirements within the processing apparatus for the separate components. 
     SUMMARY OF THE INVENTION 
     The present invention provides an apparatus for overcoming the aforementioned problems encountered with use of the liquid handling systems known to the prior art. By combining the filter element and the heating element in the same housing, the possibility of leakage is reduced because of a fewer number of fittings. Less space is required within the apparatus because only one housing is needed, and there is less pressure drop as liquid passes through only one housing. 
     More specifically, the present invention is directed to an apparatus for filtering and heating a liquid which comprises an elongate housing that is internally divided by a partition into two similarly extending chambers, an outer chamber and an inner chamber that is substantially surrounded within the outer chamber. The outer chamber has provided therein means for admitting the liquid and means for filtering the liquid. After being filtered, the liquid flows from the outer chamber to the inner chamber over a flow path defined by the partition and an end wall of the housing. The partition cooperates with a specially formed end of the housing to define a liquid flow path between the chambers in which undissolved air may be removed from the housing. The liquid then flows along a substantial length of a heating element in the inner chamber. Finally, the filtered and heated liquid is discharged from the housing. 
     The invention, and its other features and advantages, will be set forth and become more apparent in the detailed description of the preferred embodiment presented below. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     In the detailed description of the preferred embodiment of the invention presented below, reference is made to the accompanying drawing, in which: 
     FIG. 1 is a longitudinal cross-sectional view of apparatus depicting one embodiment of the invention; and 
     FIG. 2 is a cross-sectional view taken along line 2--2 of the apparatus of FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Because liquid handling systems are well known, the present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the present invention. It will be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. 
     Referring now to FIG. 1, a cylindrical housing, generally designated 10, is shown having end walls 12 and 14 and vertically extending cylindrical sidewall 16. End wall 12 may be removably affixed to the sidewall 16 by a suitable conventional over-center latching mechanism. Housing 10 is internally divided by an imperforate cylindrical partition or weir 18 into a longitudinally extending outer chamber 20 and a similarly extending inner chamber 22, the latter chamber being substantially surrounded by the outer chamber. End wall 12 comprises a molded member of, for example, a suitable plastic which cooperates with the partition 18 to define a liquid flow path for directing the counter flow of liquid from the outer chamber 20 to the inner chamber 22. It may be noted that end wall 12 at the center thereof includes a dependent portion 12a of generally conical configuration which extends downwardly below the top of the weir so that the vertex thereof is located within the inner chamber to provide a generally smooth flow path for the liquid as it flows over the weir and into the inner chamber 22. A replaceable hollow cylindrical filter element 24 of conventional construction is mounted in the outer chamber 20 and divides the chamber 20 into two parts, generally designated 20a and 20b. In the preferred embodiment end wall 12 has molded thereon an annular tapered ridge 12b which depends from end wall 12 to support and locate one end of the filter element 24. End wall 14 has associated therewith a filter holder member 29 which is inserted about the bottom portion of weir 18. Filter holder member 29 includes a cylindrical inner portion 29a which fits within the hollow end portion of the filter element 24 and an upstanding ridge portion 29b which is adapted to be pressed firmly into the bottom end of the filter element. Closure of the over center latch forces end wall 12 towards end wall 14 and the filter element is properly located and firmly supported by cooperation of filter holder member 29 and ridge 12b to provide a sufficiently liquid-tight seal so that substantially all liquid passing from outer chamber part 20a to outer chamber part 20b will pass through the filter element 24. Liquid can be furnished to the outer chamber part 20a through an inlet pipe 30 that may be connected to end wall 14. As may be noted from FIG. 1, part of the inner chamber 22 extends axially below end wall 14, and into this lower extension a liquid discharge outlet pipe 32 can be provided for removing liquid from the apparatus. Also provided within this lower extension is a threaded well 34 into which a heater, such as electric immersion heating element 36, is screwed. The heated portion of the element 36 extends axially into the inner chamber 22 of housing 10. Means are provided for furnishing electrical power to the heating element 36. Also, there may be provided means (not shown) to sense the pressure and/or temperature of the liquid to control the operation of the heating element 36. 
     In the operation of the preferred embodiment, liquid flows into the housing 10 through pipe 30 in the direction of arrow A. The liquid starts to fill part 20a (direction of arrows B) and passes through the filter 24 (as shown by arrows C) into part 20b, filling that part (direction of arrows D). The liquid, after substantially filling outer chamber 20, flows over weir or partition 18, through the liquid flow path defined by arrows E. The contour of the molded end wall 12 is such that any air entrapped in the liquid flow path is purged by the counter flow of liquid from outer chamber part 20b to inner chamber 22. Thus it can be appreciated that problems associated with the formation of stagnant air pockets within the housing 10 are substantially minimized. The presence of such air pockets is particularly undesirable since the trapped air could be heated to temperatures sufficient to melt the molded end wall 12. After the liquid enters the inner chamber 22 it flows in the direction of arrows F longitudinally along the heating element 36 and exits the housing 10 at pipe 32 (arrows G). 
     Interestingly, it has been found that other than stopping the power to heater element 36 when no liquid is being pumped into the housing, no special measures are required to prevent heat degradation of filter 24 by the substantial heat generated by heating element 36. The combination of liquid flowing in the directions of arrows D and F and the partition 18 provides sufficient insulation and protection for the filter 24. Also, since the liquid flows longitudinally along heating element 36, lower heater operating temperatures can be used to obtain the desired increase in temperature of the liquid. Furthermore, the filter element itself provides some insulation against the loss of heat which would otherwise be lost and not used for heating the liquid. 
     The invention has been described in detail with particular reference to a preferred embodiment thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.