WO1989000977A1 - Cartridge type filter for liquid purification - Google Patents

Abstract

A filter cartridge assembly incorporating a filter medium arranged between upper (4) and lower (5) pads of light, fluffy, loosely, packed fibrous matter comprising commingled, non-woven fibers of significant length relative to their diameter. The pads and filter medium are arranged within a cylindrical-shaped housing having top and bottom covers with openings sufficient to permit the free passage of both liquids and gases while substantially preventing the upper and lower pads from being dislodged from their operating positions under normal flow rate. The filter medium is preferably granulated carbon (6) of a relatively fine grain size on the order of 20 x 50 mesh said filter medium being loosely packed in the housing. The filter layers are formed from flossy fibers. The upper and lower filter pads and filter medium extend over the entire inner diameter of the cartridge, which diameter is sufficiently large relative to the thickness of the cartridge so as to produce a small pressure drop at the rated flow nominal of fluid through the cartridge.

Description

  
 



   Cartridge type filter for liquid purification
FIELD OF THE INVENTION
 The present invention relates to filtration systems and more particularly to a novel filtration cartridge for use in filtration systems and capable of providing highly efficient filtration of liquids which may have particulate matter concentration, said liquids passing through the cartridge at a very low velocity.



   A variety of different machines and systems in today's technologically oriented society employ filters and specifically cartridge type filters. The variety of cartridge type filters available for the purification of liquids, vapor and gases are legion.



   Generally, cartridge type filters have several common characteristics which include a filtering and/or purification medium (varying degrees of porosity depending upon the application) which medium is "sandwiched" between porous disk members (also of varying degrees of porosity depending upon the application). The aforementioned "sandwich" of disk members arranged on opposite sides of the filter medium is generally mounted within a hollow enclosure, typically cylindrical in shape, and having end caps each containing at least one port or inlet (or outlet) orifice for both the inlet and outlet of the fluid, said end caps generally serving the dual functions of physical support and containment of the filtering elements.  



   The end caps may alternatively contain a multiplicity of openings or are perforated or screened, with the mesh or size of the screen openings being a function of the filtering application for the fluid involved.



   As one more specific example, the prior art includes cartridge type filters in which fibrous and other types of porous filters are used in conjunction with activated carbon per se or combined with other water treatment and/or purifying agents added to the activated carbon, with all of the aforesaid components enclosed in a rigid housing capable of withstanding water line pressure at levels normally encountered in private homes and apartments, for example.



   The cartridges described above, are generally either connected in series in a pipe or conduit carrying the water to be treated or are connected at the end of a water line, such as, for example, the filter cartridges releasably mounted upon the end of a sink faucet.



   Filters of the aforementioned type require relatively high water pressure for successful operation (typically of the order of 30 psi). These pressure levels are necessitated due to the considerable hydraulic resistance to the flow of liquid through the cartridge due to filter density (i.e. the very small and even microscopic pore spaces found in porous filters) and/or the tight packing of carbon particles provided in such filters. One type of filter employed in such water in-line applications uses  a "carbon block" comprised of sintered carbon granules having microscopic interstices to prevent the passage of cysts and other bacterial contaminants, for example.



   In addition, filters of the above class fail to provide means for desorption of contaminants that have been adsorbed by the activated carbon. For example, for a given charge of activated carbon, only a strictly limited quanity of trihalomethanes can be adsorbed. Above this limit, these and other toxic compounds pass directly through the filter and thus remain in the water delivered to the user.



   The typical elements employed in cartridge type filters and their disadvantages and shortcomings will now be considered.



   The porous disks or pads employed in conventional filter cartridges include paper cloth and felt.



   Paper or paper-like materials in thin sheet form are distinguished by their significantly reduced thickness, typically of the order of 0.2mm to 0.4mm.



   Paper filters of such small thickness tend to clog up rapidly when challenged by a fluid containing high concentrations of entrained particulate matter. The particles carried by the fluid tend to accumulate upon the inlet surface of the paper filter as the fluid passes through the filter paper, and the paper filters have very little penetration distance into which such matter may move. Accordingly, large and small particles alike will pack into  one another to form a   "cake",    and, in a relatively short span of time, i.e. after a relatively small volume of fluid has passed through the filter, the collected particles create an impenetrable barrier necessitating premature cartridge replacement.



   Paper filters are generally tight-pored due to the nature of their manufacture and thus normally serve as a satisfactory means for removing fine particulate matter which nevertheless subjects the filter paper to early blockage and the need for frequent replacement due to their short useful operating lives, thus necessitating tedious and time consuming disassembly, filter removal, filter replacement and reassembly.



   Fabric filters, which are typically woven, suffer from the same shortcomings.



   Felt (a cloth formed of wool or fur often mixed with other natural synthetic fibers and bonded together through the action of heat, moisture, chemicals and pressure) is also employed for forming the porous disk or padded material, specific examples of such structures including woven pad polyester fiber felt and polyester fiber felt.



   In practice, and due to the physical characteristics of the raw materials as well as certain manufacturing limitations, felt porous disks and pads are considerably greater in thickness than paper or fabric filters and generally range from   0.5mm    to several millimeters in thickness and are typically specified by their weight (in ounces) per square  yard of felt "blanket". Typical weights are usually of the order of 10 to 12 ounces per square yard, for example.



   The resistance to fluid flow of a filter material is typically a function of its thickness, the degree of compression, packing or bonding of its fibers, the diameter and nature of the fibers employed, the sizing, chemical treatment, heat treatment and pressures used in the manufacture of the filter, fluid velocity and average velocity of the fluid flowing through the filter. The velocity of the fluid of any section of the filters is a function of both the flow rate and the area across that section and the velocity is also controlled by the fluid pressure available to cause the fluid -to flow.



   Finally, the time it takes for a filter to clog, for a given a velocity of fluid flow therethrough, is additionally a function of the concentration of particulates within the fluid and the spectrum of sizes and the nature of the particulate matter entrained within the fluid.



   All other things being equal, felted filters (like their paper filter counterparts) are capable of efficient removal of fine particulate matter, and have a greater ability to resist clogging than porous paper filters due to the fact that, for a given size (i.e. surface area) filter, in order to obtain the same hydraulic and particulate removal properties of the paper filter, the felted filter must be much thicker than the paper filter. Accordingly, the "cake" of particular matter that builds within  the felt filter is spread over a larger volume of fibers since the particulate matter penetrates to a greater depth within the thickness of the felt filter, as compared with paper filters.



   Rigid, hard, sintered micro-pored materials such as pressed carborundum blocks and ceramic materials are employed in place of the filter paper and pads described hereinabove to remove fine particulate from the fluid stream when high fluid pressures are available.



   Such rigid disks are typically on the order of 0.5mm to several millimeters in thickness. Generally, highly pressurized fluids are required for successful operation of filters employing such micro porous disks elements. The ceramic type filter disks however, can not be used in low pressure applications which, for example, rely upon simple gravity flow under low heads.



   All other factors be equal, the micro porous disk has the greatest tendency to clog when challenged with particulate matter carried by the fluid since such disks are the thinnest, hardest and least penetratable of the types described hereinabove.



  BRIEF DESCRIPTION OF THE INVENTION
 The present invention is characterized by providing a cartridge assembly capable of overcoming the disadvantages of conventional cartridges and capable of fulfilling at least the following general conditions:  
 1. The liquid (typically water) being purified and flowing through the cartridge and all of its components is heated to and maintained at relatively high temperature (that of water boiling at atmospheric pressure - about   2l20F    at sea level) for most of its passage through the filter cartridge and its enclosed components necessitating the ability of the cartridge to withstand such temperatures and to provide effective filtration in the presence of such temperatures;
 2.

  At its inlet side, the filter cartridge is typically open to the atmosphere which permits the venting of steam vapor, unwanted gases contaminating the water, and other volatilized chemical pollutants that are expelled from the water, and/or have been desorbed from the activated carbon - the internal structure of the carbon as well, providing free passage therethrough to permit venting of such pollutants through the cartridge to and out of the inlet side;
 3.

  The cartridge filter presents little resistance to liquid flow at the rated flow rate of the water being purified, the pressure drop, for example, being only about 0.25psi (lbs/square   inch),    which is only of the order of 1 percent   (1)    to 2 percent (2%) of the pressure drop obtained in conventional series - connected cartridge type line filters, enabling the cartridge filters of the present invention to be used in applications where the force of gravity alone as well as a very low magnitude head is available to produce water flow through the  cartridge and its contents and such that adequate flow rates are obtained under operating conditions of extremely low head;
 4.

  When flow is gravitional and downward through the cartridge and its contents, then both the inlet and the outlet ends of the filter of the present invention can be open to the atmosphere, which condition permits considerable aeration of the water being purified, and affords opportunity for the venting of undesired vapors and gases;
 5. In the event that upward flow of water through the filter and its contents is desired for a particular water purifying system design, then, in another embodiment of the invention to be described herein, the inlet (lower) end is capped (i.e. closed) and provided with an inlet pipe connection which closes off the inlet end from the atmosphere.

  In such cases, only a low head mechanical, thermal or other type of pump is required to overcome the small total head of the cartridge filter and contents; again, on the order of 0.2 to 0.3 psi pump output, depending upon the specific construction and rated flow through the cartridge filter;
 6. The cartridge must be capable of providing superior filtration at a low flow rate which is accomplished by dimensionally structuring the cartridge to achieve maximum throughput while maintaining the desired level of filtration capability.  



   The above criteria are met and in fact surpassed with the filter cartridge designed in accordance with the present invention which is characterized by comprising a hollow, preferably cylindrical housing capped at both its axially opened ends with perforated end caps whose openings are sufficient to retain the contents in place under normal operating conditions.



  Fluffy substantially uncompressed blankets or layers of commingled, non-woven fibers, several such blankets forming both the upper and lower pads, are arranged adjacent the respective end caps of the housing, the lower pad at the outlet end preferably being of greater thickness than the pad at the inlet end. The nature and the thickness of the pads are such as to provide relatively easy penetration of particulate matter into the depth of the pad whereby the collection of particulate matter extends over a substantial volume of the pads to significantly reduce clogging and premature replacement of the pads, as well as providing substantially un-impeded pathways for egress and venting of volatized matter as well as providing the least resistance to fluid flow during the long useful operating life of the filter cartridge.



   A filter medium which is typically activated carbon is placed between the pads and has a mesh size in the range from 20 to 50 mesh and further usually containing a small amount of extremely fine carbon particulates as "dust", the carbon being loosely packed within the cylinder and between the aforesaid pads.  



   Both the pads and the filter medium extend over the entire exterior diameter of the housing which is preferably greater in the height of the housing to facilitate filter throughput for use at extremely low flow rates.



  OBJECTS OF THE INVENTION AND BRIEF DESCRIPTION
OF THE FIGURES
 It is therefore one object of the present invention to provide a novel filter structure capable of providing excellent filtration of fluids typically passing through the filter cartridge at an elevated temperature.



   Still another object of the present invention is to provide a novel filter structure capable of providing excellent filtration of fluids passing through the cartridge at extremely low flow rates.



   Still another object of the present invention is to provide a novel filter cartridge construction in which the porous structure contributes to and facilitates the desorption of the filter medium and to the accumulation of particulate matter through a substantial volume of the filter elements to maintain good filter flow through the cartridge and to prevent premature clogging necessitating early filter replacement.



   The above as well as other objects of the present invention will become apparent when reading the accompanying description and drawing, in which:  
 Figures 1 through 3 and 6 show cross sectional views of various embodiments of filter cartridges embodying the principles of the present invention.



   Figure 4 shows a top plan view of the filter cartridge arrangement of Figure 2.



   Figure 5 shows a top plan view of the filter cartridge embodiment of Figure 1.



   Figure 7 shows a top plan view of the filter cartridge embodiment of Figure 6.



   Figure 8 shows a sectional view of a filter cartridge which is useful in explaining both the operation and advantages of the filter cartridges of the present invention.



  DETAILED DESCRIPTION OF THE INVENTION AND THE
PREFERRED EMBODIMENTS THEREOF
 Reference is initially made to Figures 1 through 5, Figures 1, 2 and 3 being cross sections of three different embodiments of the present invention, Figure 4 being a top plan view of the cartridge filter of Figure 2 and
Figure 5 being a top plan view of the cartridge filter shown in Figures 1 and 3.



   In each of Figures 1, 2 and 3, the end of the cartridge marked "A" constitutes the inlets for water being purified while "B" constitutes the outlet of the cartridge filter.



   The embodiment of the cartridge filter shown in Figure 1 is intended for use in purifying apparatus wherein both the inlet A and outlet B are open to the atmosphere. For example, the present invention maybe utilized to  great advantage in the water purification apparatus shown in copending application Serial
No. 054,571 filed May 27, 1987 and assigned to the assignee of the present invention, and incorporated herein by reference thereto.

  The water to be purified flows downwardly by gravity upon lid 2 which is shown as being recessed within housing 1 of the filter cartridge wherein the water flows through a series of perforations 2a in lid 2 and through a fibrous filter pad 4 of a predetermined thickness and continuing downward through a filter medium 6, such as for example, an activated carbon bed, or carbon mixed with another agent such as diatamaceous earth or finally ground limestone, or other purifying agent specifically added for resolving a particular contamination problem for the water being purified.

  The activated carbon (and additive when used) is loosely packed in the cartridge housing so that, under gravity and the pressure of any water that has built-up above recessed lid 2, the water being purified continues to flow downwardly through an additional fibrous filter pad 5, through the perforations 3a in bottom lid 3 and out of the perforations 3a, which constitutes outlet end B, as a stream of droplets.



   According to the method of the invention for purifying contaminated drinking water, the treated water droplets are collected and then reintroduced, for example, by thermal or other pumping means from outlet B to inlet A a number times before the process of purification is completed, the water under treatment being  raised to an elevated temperature level at the boiling point of water during the filtration operation. A more detailed description of the method and apparatus for performing said method is set forth in the aforementioned copending application Serial No. 054,571 filed May 27, 1987.



   Figure 2 shows an embodiment of the present invention providing actions similar to that obtained through the embodiment of Figure 1 wherein the cartridge is additionally provided with a central opening 7 through which a tube 11 extends. Tube 11 is provided as a conduit for hot water and vapor delivered from beneath the cartridge assembly and which is introduced and is positioned so that, as the water being purified is pumped out of the upper end of tube 11 it flows downwardly, under the action of gravity or, if it is being forcefully pumped upwardly through tube 11, is deflected downwardly so as to flow towards the inlet area
A and then proceeds through the cartridge and all of its contents as was described hereinabove in connection with Figure 1.



   Figure 4 shows a top plan view of the cartridge filter with the central opening 7 through which tube 11 carries heated water and steam upwardly for ultimate deposit upon the top lid 2.



   Figure 3 shows still another embodiment of the present invention in which the inlet A and outlet B ends are reversed from the arrangements shown in Figures 1 and 2. Liquid is introduced through conduit 8, initially  builds up in the region between the closed bottom 12 and plate 3a and continues build up so that the surface level rises through the perforations 3a and plate 3, through pad 5, activated charcoal 6, pad 1, the perforations 2a in plate 2 and ultimately above the lid 9 of housing 1 whereupon the liquid overflows the lid and flows downwardly along the sides of housing 1 and into a vessel where it is collected typically for the purpose of being reheated and then reintroduced into the filter cartridge by thermal or mechanical pumping, for example, through conduit 8.

  An embodiment of the type just described is also described in detail in the aforementioned copending application Serial
No. 054,571 filed May 27, 1987 which is incorporated herein by reference thereto. The constituents of the filter cartridges described hereinabove, will now be considered in greater detail.



   The filter pads 4 and 5 are flossy layers which by virtue of their structure and dimensional characteristics yield a distinctly novel and unique structure, especially from the point of view of the operational characteristics obtained, as compared with conventional designs.



   Floss, as used herein is defined as a fluffy, fibrous material which alternatively may also be designated as a ("type of fiber") wool pad; "wool" (i.e. fiber wool, plastic wool, steel wool etc.) being a filamentous mass of nonwoven fibers that may be animal wool or other natural fibers and/or a large number of synthetic fibers (such as plastic fibers).  



   The pads or layers utilized in the present invention are thicker, considerably softer and certainly much more "fluffy" than conventional pads and thus are much more penetratable by particulate matter than hard sintered stone, paper thin disks and felt disks known to the art.



   Accordingly, all other things being equal, the flossy layers of the present invention compared with the aforementioned conventional types, produce an entirely unexpected effect by virtue of the physical differences whereby the flossy layers of the present invention provide a filter element that is:
 the least prone to clogging and providing the least resistance flow during the long useful operating life of the filter. The loose arrangement of fibers provides very small resistance to fluid flow and does not lead to displacement, distortion or destruction of the floss pads due to the limiting pressures of fluid flow rates used in the filtration process.



   In the examples to be set forth hereinbelow, reference will be made to the particular application of low hydraulic head, gravity flow of a liquid (i.e., the water being purified). Although the examples to be given hereinbelow describe the filtration of water, it should be understood that the present invention is useful for a wide range of fluid applications (i.e., liquid, gas and vapor - being subjected to filtration either individually or in combination).



   Figures 6 and 7 show a typical filter cartridge assembly comprised of an upper flossy  layer 21 in the form of either polyester fiber floss or polyester wool, formed of undulating commingled fibers, and a lower flossy layer 22 of the same structure. In the preferred embodiment, the thickness of lower pad 22 is greater than that of upper pad 21. However, a certain latitude in thickness is possible, depending upon the liquid application (pressure available) and the concentration of suspended particulate matter being carried by the liquid, such that both layers can be made of substantially the same thickness if that is desirable without any significantly large change in the operating characteristics of the cartridge filter.



   The floss pad employed in laboratory and field tests was manufactured from polyester fibers have diameters extending over a range and averaging between 0.0005 and 0.0007 inches (about 10 micron) in diameter, each fiber being of considerable length compared with its diameter, said fibers having lengths extending over a range and preferably on the order of 0.25 to 3.0 inches, there being a mixture of fibers between the lower and upper ranges of both length and diameter.



   The fibrous material employed is typically provided by the manufacturer in loosely rolled, uncompacted "blankets" having an uncompressed thickness of the order of 20mm.



   The specific weight of compressed flossy layers of the type described hereinabove is approximately 0.00066 grams per cubic  centimeter. Such material compressed as in a felt blanket corresponds to a felt with a weight of the order of 2 ounces per square yard.



   The manner of assembly of the embodiment shown in Figure 6 is as follows:
 Four thicknesses of the polyester floss blankets were utilized to provide the circular lower pad or layer 22 so that it completely fills the inner diameter of the circular-shaped end cap 25. The lower end of cylindrical housing 24 is then pressed into lower cap 25 and is force fitted therein so that lid 23 tightly compresses the marginal portion of floss pad 22 between the inner surface of cap 25 and the outer surface of cylindrical housing 24, substantially preventing water or any other liquid from escaping through the seal formed by end cap 25, housing 24 and the marginal portion of pad 22. Cap 25 may be thermally spot welded or otherwise sealed to cylinder 24 if both of these components are formed of polyproplene, for example.



   Granulated carbon of relatively fine grain size (for example 20 x 50 mesh including several percent of extremely fine carbon particles as "dust") is then loosely packed in cylindrical housing 24 and upon filter pad 22 whereby the filter medium reaches a height which fills cylinder 24 to about 85 percent of its volume as shown in Figure 6. It should be noted that under the weight of the carbon, the polyester floss pad 22 is compacted to about one-half of its thickness, i.e., is reduced to a thickness on the order of 4cm from an original thickness on the order of 7 or 8cm when uncompacted.  



   The upper portion of the cartridge assembly is sealed with a pad or layer comprised of three thicknesses of the polyester floss material cut to form circular disks which occupies substantially the inner diameter of upper end cap 26 which is then pushed into and sealed over the lid 23 provided in the upper end of cylindrical housing 24 in a manner substantially the same as that utilized to mount end cap 25 and pad 22 upon the lower end of cylindrical housing 24. "Cylindrical" as used herein is defined as any substantially regular cross sectional shape such as square, rectangular, circular elliptical or any polygonal shape (pentagonal, hexagonal octagonal, etc.).



   The cartridge is now ready for use by proper placement within the water purification apparatus, such as for example, that described in the aforementioned application Serial No.



  054,571 filed May 27, 1987.



   In certain liquid and water purification applications, it is convenient to provide an integral funnel attachment 27 at the inlet end of the cartridge filter and specifically end cap 26, forming a liquid-tight seal therebetween.



   The gravity flow operation of the cartridge is as follows (making reference to
Figure 6, for example):
 Water flowing in the direction shown, for example, by arrows 28 is delivered to funnel attachment 27 and flows and penetrates the various porous materials in the cartridge, eventually flowing out of the perforated end cap 25 as denoted by arrows 30. When the flow rate  is increased beyond a predetermined magnitude, the water delivered to funnel 27 begins to rise, eventually filling the funnel until the surface level reaches the top edge of funnel 27, which level is the distance H above the bottom of the cartridge assembly shown in Figure 6.



   The anti-clogging characteristics of the filters of the present invention are explained making further reference to Figure 8 in which the fluid (liquid or gas) F carrying entrained particles 38 passes through the sandwiched construction of the cartridge including perforated inlet plate 26, inlet floss pad 21, fluid treating medium (for example, activated carbon) 31, outlet floss pad 22 and outlet perforated plate 25.



   In laboratory tests, it has been found that very large size particulate matter 32 tends to lodge on upper plate 26; large size particulate matter 33 tends to pass through the perforations 26a in upper plate 26 and is trapped on the inlet surface of floss pad 21; medium size particulate matter 34, migrates a small distance into the floss pad 21 and small sized particulate matter 35, if not trapped on a previous layer of matted floss fibers, will migrate still further into the floss pad before becoming trapped; and very small particulate matter 36 will continue its passage through floss pad 21 and be carried by fluid F until trapped at the interface 37 between pad 21 and purification and filter medium 31.



   It is important to note that, due to the selective trapping of particles of varying sizes  at different levels in the thick floss pad, a very large volume of trapping space is provided for the particulate matter being removed.



   Thus, all other things being equal, the large volume floss filter pads of the present invention are capable of trapping a larger total quantity (i.e. weight) of particulate matter entrained in the fluid than is capable of being removed by filters constructed according to conventional techniques, thereby assuring a correspondingly increased useful service life.



   2. Further, due to the early removal of the larger particles, the deeper layers of the floss filter 21 are available for trapping and collecting the finer particles so that there is no single - thin - layer in which a "cake" of particulate matter forms to clog the filter and thereby impede flow.



   Some of the very finest particulate matter, in the micron and submicron range, will continue its migration through the medium 21 and be trapped at locations along the relative long path provided. The action in trapping the very finest of particles is either almost entirely mechanical (i.e. the particle is trapped at a nexus of fibers, or in narrow interstices of granular material), or the trapping action can be due to the phenomenon of adsorption (by activated carbon, for example) into one of the many billions of small carbon pores in the activated carbon filter media.



   The outlet floss pad 22 is also of considerable thickness and, in practice, it has been found that a pad at the outlet end which is  thicker than the inlet end is preferred for the following reasons:
 1. It appears that most fluid filtration in purifying reagents (activated carbon, alumina, ion exchange resins, sand and other comminuted or pulverized materials) typically contain a small but significant fraction of extremely small particles.



   Without an outlet floss pad 22, the fluid flowing through the filter would pick-up the small particles and actual contaminate the outlet fluid 40 with these particles derived from the filter medium 31. Thus, a thick outlet pad is extremely useful to trap these particles.



   2. Any of the finest particles entrained in the fluid being filtered and purified and not trapped in a previous layer have the opportunity of being trapped in the final layers of floss pad 22 before the fluid being purified exits from the filter cartridge.



   Making to reference to Figure 6, T represents the thickness or height of the filter cartridge assembly. Proportionally, the thickness of upper floss pad 21 is about 20 percent of the height T, the thickness of filter medium 31 is about 50 percent T and the thickness of the lower floss pad 22 is about 30 percent T.



   The thickness of the perforated end plates 25 and 26 is not critical and these plates can be made of any convenient thickness of well perforated (open to flow) material and may take the form of metallic or other type of material screens, if desired. The criteria of  the perforated plates 25 and 26 is that the resistance to flow introduced by these perforated end caps should only be a small part of the total resistance collectively presented by the fibrous pads 21 and 22 and filter medium 31. End caps 25, 26 retain the pads in their proper operating positions, it being understood that the pads will not be distorted or pushed through the perforations at either the inlet end or the outlet end since the flow rate is quite low and since the pads freely permit the flow of fluid therethrough.



   The diameter D of the filter apparatus is dependent upon the flow rate of the particular application. The greater the desired flow rate (of water, for example) through the filter apparatus, the larger the surface area of the filter required. The criterion for liquid flow is that the velocity of the fluid (liquid in the example given) through the filter should be only about 0.6cm/sec; which is a very low velocity. For the example given hereinbelow, the diameter D is 1.4   T.   



   It should be noted that low fluid velocity enhances the filtration and purification for the reasons that the "residence time" of the fluid in the filter is increased and the particles will not be stripped from or prevented from settling into a nexus or into the pores of the porous material due to the otherwise high kinetic energy of the fluid entering the cartridge to be filtered and purified.  



   In a laboratory test, a prototype cartridge filter having the following dimension was evaluated:
 H - the over-all height of cartridge and funnel - 96mm
 D - inner diameter of cylindrical housing -   112mm   
 T - the inside axial length of the cylindrical housing - 70mm
 t - the thickness of each perforated end cap - 3mm
 The distance from outer surface to the outer surface of the end caps of the cartridge is 3 + 70 + 3 = 76mm. The diameter D may be the diameter of a circular cylinder or the average diameter of the cross-sectional area of the "cylinder".



   The perforated end caps were each provided with 16 openings each of 8mm diameter which were uniformally and symmetrically disposed over the planar surface of the end caps.



   The cartridge assembly was provided with 450 cubic centimeters (weighing about 240 grams) of a 20 x 50 mesh activated carbon.



   The upper floss pad was slightly compressed when the cartridge was sealed and its thickness was of the order of 0.2 T which in the present case was   14mm.   



   The lower floss pad was compressed by the weight of the carbon to a thickness of the order 0.25 x 70 =   18mm,    approximately.



   In use (especially with hot and boiling water) and when wetted, the thicknesses of the  floss pads was reduced by about 20 percent or so as compared with their thicknesses when dry.



   The cartridge having the aforementioned dimensions passed the maximum flow of water with water backed up to the top of funnel 27 of four liters per minute (approximately over 1 gallon per minute).



   The hydraulic head moving the water through the filter corresponds to the height H which in the present example is 96mm of water.



  The height is equivalent to the resistance drop across the filter cartridge, which in other equivalent units is only 0.14psi (lbs/sq in), which is a very small pressure drop indeed for a flow rate-of approximately 1 gallon per minute.



   The velocity of the water flowing through the filter was, on the average of 0.7cm/sec which corresponds to the criteria for velocity stated hereinabove.



   Although a paper porous disk or felt porous disk could be designed to pass a similar flow rate of water at a correspondingly small head loss or pressure drop, such results could only be accomplished by increasing the porosity of both the paper and felt disk very significantly in order to permit use of a filter pad of the same diameter D of the prototype set forth hereinabove. To maintain the same pad diameter it would be necessary to reduce the hydraulic resistance of the filter and increase its porosity. By making both the paper and felt structures extremely thin and with large apertures between their fibers. Such structures would become entirely ineffective in the  filtering of small particles of contaminants entrained in the water being filtered and purified.

  Considering a sintered ceramic type disk, it would be effectively impossible to design such structures for the application of the present invention.



   In addition, the activated carbon or other granular reagent would have to be extremely well graded and devoid of fine particles since the fine particles would pass through the filter and lower pad and be added as contaminants to the water being filtered - and supposedly being purified - since these fine particles would be picked up by the water flow through the carbon bed and passed through the thin and open porous filtered disk along with the otherwise "treated" water.



   Summarizing, the conventional structures set forth hereinabove, and which are available in the prior art, in order to accomplish the results of the present invention would offer high resistance to fluid flow or pass fine particulate matter or be subject to blockage by formation of a particulate barrier which would result in a filter structure which is impractical and in fact inoperative.



   By comparison, the filter cartridge of the present invention has been found to prove itself reliable and has satisfactorily reduced particulate levels of materials causing turbidity, undesirable odors and unpleasant and foul taste in water. Due to its operation at high temperature it is capable of producing water without any traces of vegetative  bacteria. Additionally, the filter structure reduces levels of many toxic organic compounds to exceptionally low values and significantly reduces concentrations of toxic heavy metals.



  High concentrations of minerals causing hardness have been significantly reduced.



   By virtue of its construction and the temperature range over which the filter described hereinabove is used (boiling hot water and vapor pass through in according to the method of the invention) a significant degree of desorption of volatile compounds occurs, freeing the activated carbon to absorb still more high molecular weight organics than is the case in conventional activated carbon closed cartridge filters. The open porous design of the cartridge structure of the present invention further facilitates venting of such desorbed matter to the atmosphere.



   The pressure drop across the filter is only approximately one-quarter pound per square inch (psi) which is a small fraction of typical drops across carbon line filters in which pressure requirements reach 20 psi or so at rated capacity and thus have a pressure drop which is approximately 80 times as great as the pressure drop encountered in the present invention.



   A latitude of modification, change and substitution is intended in the foregoing disclosure, and in some instances, some features of the invention will be employed without a corresponding use of other features.



  Accordingly, it is appropriate that the appended  claims be construed broadly an in a manner consistent with the spirit and scope of the invention herein described. 

Claims

WHAT IS CLAIMED IS:

1. A filter assembly comprising a container having an inlet and an outlet; a first flossy fibrous filter covering said inlet; a second flossy fibrous filter covering said outlet; a filter medium of activated carbon particles being loosely arranged in the region between said first and second filters, said filter medium and first and second filters having a porosity to permit matter desorbed from the carbon particles to freely escape through said first and second filters and be vented to the atmosphere.

2. The assembly of Claim 1 further including a holder receiving said filter assembly and having a plurality of openings at said inlet and at said outlet to facilitate the flow of water therethrough, said openings providing the least flow resistance as compared with said first and second filters.

3. The assembly of Claim 2, wherein the porosity of said first and second flossy fibrous filters and said carbon particles is chosen to be sufficiently great to facilitate the flow of water through the filter assembly from inlet to outlet at a relatively low pressure drop.

4. The assembly of Claim 3 wherein the pressure level is determined solely by gravity and the head available for producing through the filter and is determined by the height of the assembly which is measured between said inlet and said outlet.

5. The assembly of Claim 4 wherein the height of said assembly is no greater than approximately 20 centimeters.

6. The assembly of Claim 2 wherein said holder is a hollow, substantially cylindrical container and the upper and lower ends of said container respectively define said inlet and said outlet.

7. The assembly of Claim 6 wherein said inlet and said outlet ends each include a plurality of openings.

8. The assembly of Claim 7 wherein said openings have a diameter of the order of one centimeter.

9. The assembly of Claim 6 further comprising a hollow tubular member extending through said container for delivering water upwardly through said cylindrical container to an outlet opening thereof positioned above said container inlet, enabling the water leaving said tubular member to drop into said inlet under the influence of gravity and thereby percolate downwardly through the filter assembly.

10. The assembly of Claim 9 wherein said tubular member extends through said first and second filters and through the region containing said carbon particles.

11. The assembly of Claim 10 wherein said tubular member is substantially aligned with the longitudinal axis of said cylindrical container.

12 The filter assembly of Claim 1 wherein said first and second filters are each comprised of a layer of flossy fibrous matter having an uncompressed specific weight approximately 0.010 grams per cubic centimeter.

13. The filter assembly of Claim 12 wherein said first and second filters are each comprised of a at least one layer of the specific weight described in Claim 12.

14. The filter assembly of Claim 13 wherein the thickness of the second filter layer is greater than the thickness of said first filter layer.

15. The filter assembly of Claim 12 wherein said fibrous matter is formed of spun polyester fibers.

16. The filter assembly of Claim 15 wherein said layer of fibrous matter has an uncompressed thickness of the order of two centimeters.

17. The filter assembly of Claim 1 wherein said container outlet is located vertically above said inlet, said container including means for introducing water into said inlet whereby the water introduced into the container fills the filter assembly and undergoes filtering as the water rises through said filter assembly and ultimately passes through said outlet when the filter assembly is filled to overflowing whereby the filtered water runs down the sides of the container.

18. The filter assembly of Claim 1 wherein the low resistance to liquid flow through the filter assembly is small enough to permit a pressure drop of as little as 0.25 psi to assure substantially unimpeded flow of water therethrough, said low resistance being obtained by the porosity of the first and second filters and the loose packing of the filter medium in said container.

19. The filter assembly of Claim 1 wherein the first and second fibrous filters are formed of a non-woven fibrous layer comprised of loosely commingled fibers, capable of providing adequate filtering of particular without displacement and/or destructions of the filter at a pressure level of the order of less than 5% of the pressure levels encountered in conventional in-line series connected cartridge-type filters.

20. The filter assembly of Claim 1 wherein the low packing density of the carbon particles and the high porosity of the first and second fibrous filters is sufficient to substantially freely permit contaminants adsorbed by the activated carbon to be desorbed and escape from said filter assembly inlet and/or outlet when water substantially at the boiling point passes though the filter assembly.

21. The filter assembly of Claim 1 wherein material capable of inducing particulate matter to agglomerate is mixed with the carbon particles.

22. The filter assembly of Claim 1 wherein a material is mixed with the carbon particles to inhibit the growth of bacteria.

23. The filter assembly of Claim 1 wherein at least one of the additives taken from the group consisting of diatemaceous earth, limestone and silver oxide is mixed with the carbon particles.

24. The filter assembly of Claim 1 wherein the porosity of said first and second filters is sufficiently great and the density of the loosely packed carbon particles is sufficiently low to permit water having a pressure head of less than about 0.5 psi to pass through the interstices of the filter assembly at the rated flow capacity of the filter assembly at the filter's nominal flow rate.

25. A water purification apparatus comprising, in combination, the filter assembly of Claim 1 and a vessel for receiving said filter assembly positioned above the bottom of said vessel for collecting water passing through said filter assembly and the outlet thereof; said vessel having an opening adjacent to and above the inlet of said container to permit volatized matter emitted from said filter assembly to escape from said filter assembly and said vessel into the atmosphere.

26. The filter assembly of Claim 1 wherein the container is cylindrical-shaped and has a height T and has an average cross-sectional dimensional or diameter, D, where D ranges from 0.5T to 2 or more times the value of T.

27. The filter assembly of Claim 26 wherein D = l.4T.

28. The filter assembly of Claim 26 wherein the accumulated height of the first and second filter pads is about 0.5T.

29. The filter assembly of Claim 26 wherein the height of the carbon particles layer in said container is about 0.5T.

30. The filter assembly of Claim 26 wherein the openings in the ends enclosing the container are each about lcm and are uniformly disposed over said ends.

31. The filter assembly of Claim 1 wherein the container is comprised of a cylindrical housing open at opposite ends; a pair of perforated end caps each comprised of a flange which is telescoped over an associated end of said cylindrical housing.

32. The filter assembly of Claim 31 wherein a marginal portion of each of said first and second filters is pressed between the telescoped ends of said cylindrical housing and said end caps to facilitate the provision of a fluid-tight seal thereat.

33. The filter assembly of Claim 31 wherein the end caps and cylindrical housing are formed of a plastic material.

34. The filter assembly of Claim 33 wherein the end caps are spot welded to the cylindrical housing.

35. The filter assembly of Claim 33 wherein the plastic material is polypropylene.

36. The filter assembly of Claim 31 wherein one of said end caps is provided with an integral funnel portion to permit liquid to accumulate upon the surface of said one end cap joined to said funnel when the flow rate of liquid through the filter approaches the rated maximal flow for the filter.

37. The filter assembly of Claim 1 wherein said first and second filters each comprise uncompressed flossy layers comprised of non-woven fibers.

38. The filter assembly of Claim 37 wherein said fibers have an average diameter on the order of 8 to 12 microns.

39. The filter assembly of Claim 38 wherein the average diameter is preferably about 10 microns.

40. The filter assembly of Claim 37 wherein said fibers have a length of approximately 0.25 to 3.0 inches.

41. The filter assembly of Claim 38 wherein said fibers have a length of approximately 0.25 to 3.0 inches.

42. The filter assembly of Claim 37 wherein the specific weight of the flossy layers is on the order of 0.0005 to 0.00075 grams per cubic centimeter.

43. The filter assembly of Claim 42 wherein the specific weight of the flossy layers is preferably about 0.00066 grams per cubic centimeter.

44. The filter assembly of Claim 37 wherein the flossy layers are comprised of undulating non-woven fibers which are loosely arranged in said layers to provide a very high porosity sufficient to enable particulate matter carried by a fluid passing through said pad to penetrate deeply into said layer to provide for collection and accumulation of particulate matter over a substantial amount of the volume of said layer to prevent premature clogging of the filter layer.

45. The filter assembly of Claim 44 wherein the large porosity, loose commingling of said fibers is substantially undisturbed and is sufficient to prevent displacement of the fibers within the flossy layer when the flow rate therethrough is less than 1.0 cm per second.

46. The filter assembly of Claim 44 wherein the large porosity, loose commingling of said fibers is substantially undisturbed and is sufficient to prevent displacement of the fibers within the flossy layer when the pressure drop applied to said flossy layers from the source of liquid flowing to said layer is less than 1.0 psi.

47. The filter assembly of Claim 44 wherein the large porosity, loose commingling of said fibers is substantially undisturbed and is sufficient to prevent displacement of the fibers within the flossy layer when the pressure drop applied to said flossy layers by the fluid is less than about 1.0 psi.

48. The filter assembly of Claim 45 wherein the openings in the ends of the container are sufficiently large to provide less resistance to liquid flow as compared with said first and second filters and said filter medium.

49. The filter assembly of Claim 48 wherein the size of said openings are sufficiently small to prevent the flossy filter layers from being distorted and forced into said openings when fluid flow velocities are maintained below 1.0 cm per second.