Abstract:
A multiple fluid filter apparatus is disclosed having a locking arrangement for securing multiple filter elements that accommodates different size filters, permits axial expansion and contraction of the filters, yet prevents warping.

Description:
This application is a continuation of PCT/EP99/04216 filed on Jun. 17, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     Filter housings equipped with several filter elements such as filter cartridges or wound modules are used, for example, for pressure filtration of fluids such as liquids and gases for separation of undesirable components such as heavy metal ions, microorganisms from waste water or beverages, for the concentration of proteins, for sterile filtration in the pharmaceutical industry, and so forth. Such filter elements are subjected to mechanical loads during both filtration and filter cleaning. The bending or warping of plastic filter elements in their longitudinal axis has a particularly serious effect in that it results in damage to the filter elements, including the filter materials, rendering them unusable. Such warping is caused primarily by flow turbulence, by pressure surges, and by backflushing. 
     Attempts to prevent such warping of the filter elements by means of locking devices is known. For example, Soviet Union Patent No. 17 54 157 Al discloses a multiple filter housing with several filter elements that are accommodated on the permeate side by a base plate. Above the filter elements on the feed side there is a plate-shaped contact pressure device through which adjusting screws are inserted to the end caps of the filter elements in order to lock them in place. The plate-shaped contact pressure device is attached to a central spacer rod. With this locking device, differences in the overall heights of the filter elements can also be accommodated on an individual basis by the adjusting screws. However, a major drawback to such an arrangement is that the filter elements cannot expand along their length at varying elevated temperatures such as are encountered with inline superheated steam sterilization, which can still lead to warping damage of the filter elements. Other drawbacks of this arrangement are that the locking device consists of many components, which makes assembly and disassembly of the filtering apparatus very time-consuming, and that the multiple components have numerous edges and cavities that are difficult to clean. Moreover, such a design does not comply with generally accepted regulations of the U.S. Food and Drug Administration (FDA), does not comply with FDA Good Manufacturing Practices and generally does not provide a satisfactory technical solution. 
     It is therefore a principal object of the invention to provide a multiple filter apparatus with a locking device for filter elements from a minimal number of components whereby bending or warping of the filter elements is prevented, differences in the length of the filter elements caused by manufacturing tolerances are tolerated, and thermal expansion and contraction of the filter elements is permitted. Another object of the invention is to provide a multiple filter apparatus with a locking device that is simply constructed and easy to lock, and that has a minimal number of parts that are difficult to clean. 
     These objects and others which will become apparent to one of ordinary skill in the art are provided by the present invention, which is summarized and described in detail below. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention comprises a multiple filter housing consisting of a housing dome and a housing base with a base plate, the housing being equipped with a locking device consisting of a spacer rod and a centering plate. The housing is provided with connections for the feed and discharge of fluids and accepts a number of cartridge-type filter elements, such as filter cartridges or spiral wound modules, that are accommodated and affixed to the base plate in conventional fashion so as to divide the feed and permeate zones, whereby the fluid to be filtered proceeds from one zone to the other only through the filter material of the filter elements by the application of a pressure difference between the feed and permeate zones. The filter elements have guide adapters on their ends distal to the base plate which have a smaller diameter than the overall diameter of the filter elements themselves and that usually taper at the top. The multiple filter housing can be operated in any position, but is preferably operated so that the filter elements stand upright, i.e., the guide adapters point upward. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 is a vertical section through an exemplary embodiment of a multiple filter housing according to the invention. 
     FIG. 2 is a plan view of an exemplary centering plate according to the invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Referring to the drawings, wherein the same numerical references refer to the same elements, there is shown in FIG. 1 a multiple filter apparatus comprising a housing  1 , the housing consisting of a housing base  2  having feed inlet  3  and filtrate outlet  4 , a housing dome  5  with a vent  6  and optional handle  7 . Base plate  8  is shown accommodating a plurality of cartridge-type filter elements  9  of a single model size which are provided with guide adapters  10  that have tapered segments  16 . The locking device consists of a spacer rod  11  and a centering plate  12 . Centering plate  12  accepts either the filter elements  9  or the guide adapters  10 . Spacer rod  11  is attached at its end perpendicular to housing base  2  or base plate  5  and lies on the median axis of multiple filter housing  1 . Spacer rod  11  has three distinct segments  13 ,  13 ′ and  13 ″ and two locking profiles  15  and  15 ′ in the sections  14  and  14 ′, respectively: in the embodiment of the invention shown, the area of the first end segment  13  of spacer rod  11  begins above guide adapter  10  and ends above the tapering segment  16  of the guide adapter, while the lower border of section  14  with locking profile  15  is positioned at the height of the guide profile  17  of the guide adapter. The free end of the spacer rod  11  is inserted through the locking opening  18  of centering plate  12 . Centering plate  12  rests on a lower stop of section  14  of the spacer rod, or on the guide profile  17  of the guide adapter, whichever has the greatest overall height. Centering plate  12  is initially movable radially around and axially along spacer rod  11  as it is mounted in the area of the first end segment  13  and, in the area of section  14  with locking profile  15  in locked position, is only movable axially along spacer rod  11 . Shorter filter elements may be secured by a centering plate locked on locking profile  15 ′. 
     As shown in FIG. 2, centering plate  12  has openings  19 ,  20 , and  21  to accept guide adapters  10 . Opening  21  is shown as an oblong hole to facilitate locking and unlocking. Locking opening  18  is keyhole-shaped, formed of a circular aperture  22  with a notch  23  having a smaller width than the diameter of the circular aperture  22 . The center of the notch  23  coincides with the center of centering plate  12 , whose outermost peripheral regions lie on a circular arc that is slightly smaller than the internal circumference of the multiple filter housing. Circular aperture  22  of locking opening  18  serves to guide spacer rod  11  through locking opening  18  when centering plate  12  captures guide adapters  10  with openings  19 ,  20  and  21  by turning and lowering the centering plate  12 , and, after the area  14  of the spacer rod has been reached, to move the centering plate  12  with its notch  23  over the locking profile  15  of spacer rod  11 , thereby achieving locking. Centering plate  12  is also equipped with another opening  24  formed as an oblong hole, which is in contact at its outer periphery with the closed housing dome  5  and assures locking. In the embodiment of the centering plate  12  shown, openings  21  and  24  and locking opening  18  are aligned along an axis S-A, which forms an axis of symmetry of centering plate  12 . This construction, which is asymmetric with respect to every other axis, assures the correct and secure installation of the centering plate  12 , even by personnel with little experience. 
     As mentioned, centering plate  12  of the locking device has a locking opening  18  and openings to accommodate either the filter elements  9  or the guide adapters  10  of the filter elements. Spacer rod  11  is perpendicular to and rigidly attached to housing base  2 . It has a locking profile  15  in at least one area  14  of a first segment  13  and another locking profile  15 ′ in at a least one area  14 ′ of a second segment  13 ′. In a preferred embodiment of the invention, the at least one area of the first segment  13  is the end segment of the free end of spacer rod  11  and begins above guide adapters  10  and ends within the upper half, preferably within the upper third, of filter elements  9  or, in an alternative embodiment, within the tapered segment  16  of guide adapters  10 . The at least one area of the second segment  13 ′ of spacer rod  11  with locking profile  15 ′ reaches halfway up the length of the rod at the most, preferably as high as the end of the upper third of filter elements  9 . In an alternative embodiment, the lower terminus of the segment  13  with the locking profile  15  is positioned at least at the height of the guide profile  17  of the filter element guide adapters  10 . 
     In the case of two centering plates, spacer rod  11  penetrates locking opening  18  of each centering plate  12  with its free end in such a way that the centering plates are radially movable around spacer rod  11  in the area of the first segment  13  and in the area of the second segment  13 ′, but with the respective locking profiles in locking position, the centering plates are only movable axially along spacer rod  11 . During assembly, a given centering plate  12  with its locking opening  18  is slid to the first segment  13  of spacer rod  11  and turned radially until its openings  19 ,  20  and  21  can accept the guide adapters  10 . It is then lowered in the axial direction and locked with the locking profile of the spacer rod. In locking position, an orthogonal adjustment of filter elements  9  in relation to base plate  8  is ensured, so that housing dome  5  can be readily mounted and secured to housing base  2 . 
     Locking profiles  15  and  15 ′ of centering plate  12  preferably have a key-shaped cross section to mate with locking opening  18 , comprising a generally circular portion and a generally rectangular portion with the rectangular or notch portion having a width less than the diameter of the circular portion. To achieve locking, spacer rod  11  is pressed in the direction of this notch in such a way that the locking profile  15 ,  15 ′ of spacer rod  11  positively penetrates the notch. The notch portion is preferably in the shape of three sides of a rectangle, preferably with rounded corners. If spacer rod  11  extends along the median axis of the multiple filter housing, it is advantageous that if the center of the notch lies on this axis and the center coincides with the center of a circle beyond which the periphery of centering plate  12  does not extend. The center of the notch thus coincides with the center of a circle (shown in dashed line in FIG. 2) that is slightly smaller than the circumference of the internal wall of the multiple filter housing. Otherwise, housing dome  5  is not attachable or centering plate  12  will at least not be horizontally mountable in the multiple filter housing. As displacement of centering plate  12  is only possible in the axial direction, filter elements  9  can only expand axially, and are not permitted to warp. If centering plate  12  only accommodates guide adapters  10  of filter elements  9  in the alternative embodiment, then centering plate  12  will simply be displaced upward by the filter elements expanding axially. In this alternative embodiment, because the lower terminus of the segment  13  with the locking profile  15  of the spacer rod  11  is positioned at the height of the guide profile  17  of the guide adapter  10  of the filter element with the largest overall height, the length of the second segment  13 ′ with the locking profile  15 ′ of spacer rod  11  is shorter than the height of the guide adapter  10  of the filter elements, and the diameter of the openings of the centering plate  12  for accepting the guide adapters of the filter elements is larger than the diameter of the guide adapters, but smaller than the diameter of the filter elements. Because of this, variance in overall height clearances of the filter elements is immaterial. 
     As filter elements  9  contract, e.g., as they cool, centering plate  12  lowers of its own weight. Centering place  12  is therefore preferably made of a heavier material such as stainless steel. In a further advantageous embodiment of the invention, centering plate  12  has peripheral recesses and/or perforations. This results in the unhindered circulation of the fluids to be filtered on both sides of the centering plate. Such recesses and perforations also alleviate fluid pressure on centering plate  12  and so counteract the tendency of the centering plate to be dislodged, which can occur during strong surges in the filtration process. For multiple filter housings with more than two filter elements, it is particularly advantageous to design the openings of the centering plate to accept the guide adapters  10  as oblong holes on the periphery of the centering plate as shown, for example, as element  24  in FIG. 2, as such a design facilitates the attachment and locking of the centering plate along the axis of symmetry of the locking opening  18 . Incorporation of such perforations on the periphery of the centering plate permits the perforation&#39;s outermost edge that coincides with the circular arc of the centering plate to serve as additional support of the centering plate on the inner wall of the attached housing dome  5 . 
     As mentioned, another advantageous embodiment of the invention is obtained if centering plate  12  is formed so that it is symmetric about the axis of symmetry of the circular aperture  22 . This allows even unskilled personnel to securely install the centering plate of the locking device. An essential advantage of the invention is that filter elements of different sizes can be used and secured within one and the same multiple filter housing. For example, in a multiple filter housing wherein the housing is designed for operation with 30-inch filter elements the operation and locking of 20-inch and even 10-inch filter elements is also possible. Similarly, in a multiple filter housing designed for operation with 20-inch filter elements, the operation and locking of 20-inch and even 10-inch filter elements is possible. If several model sizes of filter elements are used simultaneously, a number of centering plates may be used that correspond to the different model sizes, the size of their filter element/guide adapter openings or their shape varied in such a way that each respective centering plate can be lowered to the locking height of each respective smaller size of the filter elements, while the last centering plate can be lowered to the locking height of the largest size filter. Multiple filter housings with a very large number of filter elements may be equipped with several spacer rods. A number of openings corresponding to the number of spacer rods are then made in the centering plate; in such instances it will suffice if only one of the spacer rods is equipped with the locking profile(s). It is, however, also possible to provide a customized centering plate for each spacer rod. 
     The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.