Filter apparatus and filter element therefor
BACKGROUND OF THE INVENTION 
     The present invention relates to a filtering apparatus. More particularly this invention concerns a filter element usable in a filtering apparatus wherein a separable suspension to be filtered is forced under pressure into the filter element. 
     A filtering apparatus is known having a housing defining a closed chamber in which is provided a hollow shaft carrying a plurality of axially spaced filter elements. Each of these elements comprises a support normally of porous construction and a filter cloth secured to at least one face of the support. 
     As a rule such supports are round so that the filter element closely fills the interior of the chamber. Such shape also facilitates rotating the filter elements during sluicing-off of filter cake that has built up on the filter elements. The filter elements in this arrangement are rotated as a liquid is squirted on them to loosen the filter cake that is then centrifugally driven off. 
     It is also known to have nonrotatable rectangular filter elements provided in a chamber in such manner as to be nonrotatable. With the rotatable filter elements the filtrate is drawn off through the central hollow shaft on which the rotatable elements are carried, but with the nonrotatable elements the filtrate is drawn off through channels that surround the filter surfaces. 
     Various prior-art filters are described in German Pat. No. 877,742, U.S. Pat. Nos. 3,107,217 and 3,190,449 as well as in the article by B. Spiekermeier and J. Stebler appearing in Maschinenmarkt on July 2, 1974 (Vogel-Verlag Wurzburg; vol. 53). 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide an improved filtering apparatus. 
     Another object is to provide an improved filter element for such an apparatus. 
     Yet another object is to provide an improved filter element wherein the filter cloth is used advantageously, but wherein excellent cleaning of the filter elements is possible. 
     These objects are attained according to the present invention in a filtering apparatus wherein a plurality of axially spaced polygonal filter supports are mounted on a hollow shaft extending axially through a closed chamber. Each of the supports has at least one face provided with a polygonal panel of filter cloth. Thus, the material constituting the filter cloth is used with maximum efficiency. At the same time excellent sluicing of the filter cake off the filter elements can be obtained. 
     According to yet another feature of this invention the filter cloth is formed as a pair of juxtaposed and coextensive generally square panels having three sides permanently joined together so as to form a pocket. Openable means is provided joining the other sides of the panels together and the flat stiffening member or support is provided within this pocket. Thus it is possible to make a very inexpensive filter element which can readily be changed merely by opening the one side, pulling it off, and replacing it with another whose open side is then easily closed. 
     In accordance with the present invention the three sides of the filter-cloth pocket may be stitched or welded together. 
     In accordance with yet another feature of this invention the corners of the filter-cloth panels are cut off so as to give them a generally octagonal shape and the support received in the pocket constituted by the cloth is generally square and has a maximum dimension which is equal to at most two-thirds of the maximum dimension of the pocket. Thus it is possible to slip such a filter element into one open side of the generally octagonal filter cloth. 
     The support may be in accordance with this invention an imperforate metal plate either formed with corrugations or other formations giving it a nonplanar shape or may be flanked by a pair of screens so that the filter can be sucked out from within the filter-cloth pocket. 
    
    
     The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing. 
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a vertical and axial section through an apparatus according to this invention with the end cover removed; 
     FIG. 2 is a vertical cross section through the apparatus of FIG. 1; 
     FIG. 3 is a large-scale sectional view of a portion of the apparatus of FIG. 1; 
     FIG. 4a is a side view of a filter cloth in accordance with this invention; 
     FIG. 4b is a side view of the support usable with the filter cloth of FIG. 4a; 
     FIG. 5 is a side view partly broken away of a filter element as used in FIGS. 1-3 and employing the cloth and support of FIGS. 4a and 4b; 
     FIG. 6 is a view similar to FIG. 4a showing another cloth in accordance with this invention; 
     FIG. 7 shows in side view a filter element according to this invention; 
     FIG. 8 is a vertical section through the element of FIG. 7; 
     FIG. 9 is a view similar to FIG. 8 showing another filter element according to this invention; 
     FIG. 10 is a top view partly broken away of a filter element according to the present invention; and 
     FIG. 11 is a vertical section through the filter element of FIG. 10. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As shown in FIGS. 1-3 the filter apparatus according to the present invention comprises a cylindrical housing 1 having a horizontal central axis A, removable cover 1&#39; at one end and a closed opposite end 1&#34;. A hollow shaft 2 is rotatably supported on this housing about the axis A by a bearing 20 at the end 1&#34; and a bearing 21 at the cover 1&#39;. This shaft 2 is formed with a multiplicity of radially opening perforations 2&#39; so that liquid can pass inwardly through these openings 2&#39;. A motor 7 is mounted on the end 1&#34; for rotation of the shaft 2 about the axis A. 
     A plurality of rectangular filter elements 3 are carried on the shaft 2, each element 3 extending in a plane perpendicular to the axis A. Each of these elements 3 is spaced from the adjoining elements on the shaft 2 by means of spacer rings 19, and clips 10 carried on axially extending rods 9 ensure proper axial spacing of these elements 3. The rods 9 are carried on a spider 13 in a rectangular array, the spider 13 being bolted to a flange 14 on the shaft 2. In addition the shaft 2 is provided with three sets of angularly equispaced arms 23 each carrying a roller 11 that engages the inside surface of the housing 1. Thus, these rollers 11 serve to rotationally support the entire assembly shown in FIG. 3 within the drum 1. 
     During normal operation a suspension containing particles to be filtered from a liquid is fed into the apparatus by a pump P at an inlet 4 and clear filtrate leaving the interior of the shaft 2 by the outlet 6. During such operation the motor 7 is not energized so that the shaft 2 stands still. A filter medium such as diatomaceous earth is added to the suspension to be filtered at the beginning of each filtering cycle so that it forms a filter cake on the elements 3. 
     Once the filter cake has become too thick or is clogged the pump P is turned off and the motor 7 is energized. This causes the filter elements 3, the shaft 2, the rods 9, and the associated structure to rotate in the housing 1 about the axis A. Simultaneously lower outlets 5 are opened on the housing and nozzles 12 connected to a manifold 8 squirt liquid between the rotating filter elements 3. This effects an extremely thorough washing-off of the filter cake on the elements 3. 
     FIGS. 4a, 4b, and 5 show a filter element 3. This element comprises a rectangular piece 15 of filter cloth bent over so as to form a pocket in which is received a rectangular support screen 16. The edges 15&#39; of the pocket are stitched tightly together and the edges 15&#34; are closed after insertion of the screen 16 by clamping these edges between a pair or rigid bars 17 held together with screws 18. Thereafter, the entire assembly is mounted on the shaft 2 and locked in place via bolts 22 (FIG. 2). 
     FIG. 6 shows a generally square filter element 3a formed with a central hole 24 like the element 3. This element 3a has cut-off corners 3a&#39; which are straight and have a length 1 equal to less than one-third the length L of the longer straight side 3a&#34; of the element 3a. 
     FIGS. 7 and 8 show how such a filter element 3a is made. It is provided internally with a metal plate 18 which is square and has sides whose length is equal to less than L. This plate 18 is surrounded on both sides with support screens 16 that are then received within the pocket 15 shown in FIG. 6. In this arrangement the plate 16 is metallic, planar, and imperforate. 
     FIG. 9 shows how the plate 18 can be replaced by a plate 19 that is profiled so that the screens 16 can be dispensed with and the cloth 15 can be applied directly over this plate 19. 
     With the arrangement shown in FIGS. 6 and 7 it has been found possible to cut off the corners of the panel 15 as indicated by removing a triangle having a base corresponding to the edge 3a&#39; with the length of 5 cm. This reduces the effective surface area of the filter element, equal to 200 cm 2  here, by 2%. At the same time the total volume of the housing 1 can be reduced by approximately 18%, by reducing its diameter by 10 cm. This makes for a considerable saving in first cost of the apparatus. 
     FIGS. 10 and 11 show an element 3b comprising an imperforate base plate 20 on the bottom, a coarse support screen 16, and a fine filter cloth 15 all of square shape. The edge is closed up on all four sides by bars 17 and screws 18 as described above. In addition a seal 21 may be provided around the screen 16 and between the cloth 15 and the base plate 20. 
     With the system according to the present invention it is therefore possible to produce a very inexpensive filter element which can readily be cleaned. Such an arrangement has the considerable cost advantages and construction advantages of the nonrotatable types with many of the operational advantages of the rotational filter types. 
     It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of apparatus differing from the types described above. 
     While the invention has been illustrated and described as embodied in a filter apparatus, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. 
     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.