Abstract:
A radial flow cartridge, especially for use with an ion exchange resin, includes inner and outer tubular cages, and a tubular knitted liner extending the length of the cartridge between the inner and outer cages and spaced apart from the outer cage. The resin medium fills the space between the liner and the inner cage. During use, the medium absorbs fluid and expands, stretching the knit liner radially and, thereby filling the space between the liner and the outer cage.

Description:
FIELD OF THE INVENTION 
   The invention relates to cartridges containing loose media that may expand in use, and especially to radial-flow ion-exchange cartridges for use in reducing the Total Acid Number (TAN) of lubrication, insulating, and hydraulic oils. 
   BACKGROUND OF THE INVENTION 
   Triaryl phosphates and other phosphate esters have been used as fire-resistant hydraulic fluids and lubricants for some years. A problem with these fluids is that they tend to degrade, especially by hydrolysis if water is present in the fluid, to generate acidic products, potentially including phosphoric acid, that may impair the properties of the fluids and/or corrode the equipment in which they are used. It has therefore been proposed to remove the acid products, and one way of removing them is by means of an ion exchange resin. This has proved to be an extremely successful solution. However, over time, the resin needs to be changed. To facilitate this, it is common to provide the ion exchange resin in a radial-flow cartridge. 
   In use, the ion exchange resin tends to swell as its water content increases, and to contract as its water content decreases. Thus, it is desirable to fill, store, and supply the cartridges with a relatively low moisture content in the ion exchange resin, both to avoid the possibility of water exuding from the cartridges in storage or handling, and to provide cartridges which are designed to absorb as much water as possible. However, it has been determined that when the ion exchange cartridges are used on fluids having a high initial total acid number (TAN), the expansion of the resin can generate forces sufficient to swell, or even burst, the cartridge. 
   To prevent bursting, partially filled cartridges have been proposed. The goal was to allow the vacant space in the cartridge to accommodate the expansion of the resin. However, since ion exchange resin is loose, it tends to settle at the bottom of the cartridge, leaving the expansion space at the top end. As such, the resin tends to pack within the cartridge. The tight packing of the resin inhibits upward movement as the resin expands. As such, the sides of the cartridge are, again, subject to excessive forces. In addition, it has been determined that a partially filled cartridge can lead to the development of pockets of open spaces through which the circulating fluid may bypass the resin, reducing the efficiency of the ion exchange. 
   A need, therefore, exists for an improved ion exchange resin cartridge which is designed to provide efficient moisture removal while reducing the occurrence of bursting. 
   SUMMARY OF THE INVENTION 
   It is an object of the invention to provide a radial flow cartridge that can reliably accommodate expansion of a medium contained within the cartridge, and a method of making such a cartridge. 
   The invention provides a radial flow cartridge having inner and outer tubular cages, and a non-rigid tubular liner extending the length of the cartridge between the inner and outer cages and spaced apart from a first of the cages. A medium fills the space between the liner and the other cage. When the medium expands, the liner stretches or otherwise deforms, allowing the medium to expand radially towards the outer cage. 
   The invention also provides a method of making a radial flow cartridge that comprises providing a cartridge that has inner and outer tubular cages and a non-rigid tubular liner extending the length of the cartridge between the inner and outer cages and spaced apart from a first of the cages. A medium for filling the cartridge, which medium tends to expand and/or contract in use, is provided. The medium is adjusted to a condition in which its volume is not substantially greater than the minimum volume that it is likely to have in use of the cartridge, and is introduced to fill the space between the liner and the first cage. 
   Preferably, the medium is located between the liner and the inner cage. The liner is preferably made from an elastic material. Circumferential tension in the liner is designed to allow the medium to expand only as necessary, while restraining unwanted expansion, thereby ensuring that voids do not develop in the medium. 
   The liner may be spaced from the first cage by one or more circumferential bands that restrict the circumference of the liner to a dimension between those of the inner and outer cages. If the first cage is the outer cage, the band may be elastic. Alternatively, the band may be effectively inelastic, and the medium may expand by expanding the liner to either side of the band. 
   Alternatively, the liner may be spaced from the first cage by one or more radial spacers extending from the liner to the first cage, which may be in the form of an annular disk, preferably with axial flanges at the rim that engage the liner. 
   When the medium expands, the liner stretches and/or deforms, allowing the medium to expand radially towards the first cage. The amount of medium is preferably selected such that at its maximum expansion expected during use the medium substantially fills the space available between the inner and outer cages. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For the purpose of illustrating the invention, there are shown in the drawings forms of the invention which are presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown. 
       FIG. 1  is an axial elevation view, partly cut away and partly in section, of a first embodiment of an ion exchange cartridge according to the invention. 
       FIG. 1A  is a an axial elevation view, partly cut away, of the ion exchange cartridge shown in  FIG. 1 . 
       FIG. 2  is an enlarged view of detail  FIG. 2  of  FIG. 1 . 
       FIG. 3  is a view similar to  FIG. 1  of a second embodiment of an ion exchange cartridge according to the invention. 
       FIG. 4  is a view similar to  FIG. 1  of a third embodiment of an ion exchange cartridge according to the invention. 
   

   DETAILED DESCRIPTION OF THE EMBODIMENTS 
   Referring to the drawings, and initially to  FIGS. 1 ,  1 A, and  2 , one embodiment of an ion exchange cartridge according to the present invention is indicated generally by the reference numeral  10 . The cartridge  10  comprises an inner cage  12  and an outer cage  14  in the form of coaxial tubes. The inner cage  12  is of mesh or perforated construction, with holes sufficiently small to prevent beads of ion exchange resin  16 , with which the cartridge  10  is filled, from passing into the inner cage. Alternately, a sleeve  17  of material may be disposed about the inner cage. The sleeve is permeable to fluid so as to permit a fluid to pass from inside the inner cage to inside the liner. If a sleeve is used, the sleeve is preferably made from spunbonded continuous filament polyester material. The material may then be 15 mils (380 μm) thick, with a basis weight of 3 oz/sq. yd. (100 g/m 2 ) and a Frazier airflow of 192 cfm (airflow of 192 cubic feet per square foot per minute at a differential pressure of 0.5 inch water (58.5 m/s at 124.5 Pa)). 
   As will be explained below, the resin  16  does not come into direct contact with the outer cage  14 . However, the outer cage  14  may be made of similar mesh or perforated material as the inner cage  12 . The cages may be made of perforated, louvered, or expanded cold-rolled or stainless steel. The steel may be coated or plated for corrosion resistance. The cages  12  and  14  may be straight or spiral continuous seamed, spot welded or can seamed, to form an open cylinder. 
   The inner and outer cages  12 ,  14  are joined at one end by a lid or end cap  22 . The end cap  22  is preferably clamped or otherwise secured to the outer cage. A sealing disk  18  is preferably located inside the cap  22 . The sealing disk  18  is preferably formed from a urethane material. The axial ends of the inner and outer cages  12 ,  14  are both preferably embedded into the urethane, thereby providing a fluid tight seal between the ends of the inner and outer cages. The sealing disk  18  and end cap  22  have a central opening  20  that opens into the space inside the inner cage  12 . A seal or gasket  24 , such as an O-ring, may be incorporated around the opening  20  to inhibit leakage between a fluid inlet or outlet that is intended to be connected to the cartridge in use. 
   A second end cap  28  is swaged or otherwise attached to the opposite end of the canister  10 . A second sealing disk  26  is placed between the ends of the inner and outer cages. The second sealing disk  26  is preferably made from urethane which is poured into the canister between the inner and outer cages. A bail  30  may be attached to the end cap  28  to assist in inserting the cartridge  10  into, and removing the cartridge from, a cartridge housing (not shown) of an apparatus with which the cartridge is to be used. 
   A tubular liner  32  is arranged between the inner and outer cages  12 ,  14 . The liner  32  is preferably attached at its axial ends to either the outer cage  12 , the inner cage  14  or the end caps. In the illustrated embodiment, the attachment is provided by folding the ends of the liner over the edges of the outer cage, then either embedding the combination in the urethane sealing disks  18 ,  26  or using the end caps  22 ,  28  to secure the liner ends. Alternately, the liner could be just attached to the sealing disks  18 ,  26 . 
   One or more retaining bands  34  are located in the middle of the liner  32 . The retaining band  34 , or each of the retaining bands, acts as a restriction on the diameter of the liner. In the illustrated embodiment, the retaining band restricts the liner to a diameter about halfway between the diameters of the inner and outer cages  12 ,  14 . Thus, the retaining band  34  forms the liner into a tube with concave sides. As discussed above, the ion exchange resin  16  fills the space between the liner  32  and the inner cage  12 . The space  36  formed between the liner  32  and the outer cage  14  is initially empty. 
   The liner  32  is preferably made from a tubular knit sleeve of polyester material. The tubular knit structure is highly beneficial since the absence of an axial seam removes a major point of weakness. The knit sleeve also has sufficient elasticity such that, when the cartridge is initially filled, the sleeve can contain the ion exchange resin  16  in the region adjacent to the inner cage  12 . However, during use, as the ion exchange resin absorbs acid and water and begins to expand, the liner  32  will stretch rather than tear. The liner  32  thus allows the resin to expand towards the outer cage  14 , into the space  36 , while still retaining it in a continuous and fairly even bed over the length and circumference of the cartridge  10 . In one preferred embodiment, the liner is made from the 150/50 200/48 #5 knit BEANE BAG TM material supplied by C S &amp; S Filtration, of Chattanooga, TN, under the item number 2K0510.5-045. This material has a weight of 13.92oz/yd 2 , a tensile strength of 76.5 lbf in the machine direction and 52.5 lbf across the machine direction, an elongation before failure of 5.109″ for an initial sample size of 3″ between jaws (170.3%) in the machine direction and 4.494″ for an initial sample size of 3″ between jaws (149.8%) across the machine direction. The material has a Frazier airflow permeability of 116.3, and a Mullens burst strength of at least 60.0 psi. 
   Another possible material for the liner is the antistatic 150/50 150/50 BEANE BAG TM material supplied by C S &amp; S Filtration under the item number 2K128.0-050 AS. The antistatic material contains a minor proportion of carbon fibers. This material has a weight of 15.21 oz/yd , a tensile strength of 56.5 lbf in the machine direction and 64 lbf across the machine direction, an elongation before failure of 4.170″ for an initial sample size of 3″ between jaws (139%) in the machine direction and 2.447″ for an initial sample size of 3″ between jaws (81.6%) across the machine direction. The material has a Frazier airflow permeability of 16.95, and a Mullens burst strength of at least 60.0 psi. However, the antistatic material is not generally necessary. 
   The retaining band or bands  34  is or are preferably formed from tubular knit polyester material and has a length of approximately ¼ to ¾ of the length of the cartridge  10 . In one preferred embodiment, the retaining band  34  is made from material the same as that of the liner  32 , but with a smaller unstretched diameter. It is also contemplated that the liner  32  could be formed with more dense or a different type of knitting in the central area where the retaining band is in  FIG. 1 . The variation in the knit liner would cause the liner to behave in much the same way as the liner in  FIG. 1  when subjected to expansion of the resin (i.e., the portion of the liner where the knit is less dense or selected to facilitate expansion would stretch more than the central portion of the liner.) This variation of the invention eliminates the need for a retaining band. 
   To assemble the cartridge  10 , one end cap  22 , including the gasket assembly  24 , is preferably swaged or otherwise attached to the end of the inner cage  12 . Urethane is poured into the canister to form the sealing disk  18 , and the outer cage  14 , with the liner  32  folded over its end, is inserted into the end cap, embedding into the urethane. The retaining band or bands  34  is or are then positioned around the middle of the liner  32 , if that has not already been done. 
   The liner  32  is also folded over the other end of the outer cage  12 . The liner  32  is drawn sufficiently taut lengthways that it adopts the curved shape shown in  FIG. 1 . The middle part is narrowed to the diameter of the retaining band  34 , and the liner bells out smoothly at either end to the diameter of the outer cage  12 . A measured quantity of the resin  16  is poured in between the inner cage  14  and the liner, filling the cartridge to within about ½″ of the top. That end is then closed by pouring in urethane and allowing it to set to form the sealing disk  26 . The end cap  28  is placed over the urethane sealing disk  26 , and swaged or otherwise attached to the end of the inner cage  12 . A bail  30  is then added. 
   One suitable ion exchange resin for use in the cartridge  10  for removing phosphoric acid from phosphate ester fluids is Hilite E, supplied by The Hilliard Corporation, of Elmira, N.Y. This resin is supplied in the form of approximately 40 mesh spherical beads. This bead size typically weighs approximately 40 lbs/cu. ft. For use in the cartridge  10 , it has been determined that the weight of resin can be reduced by first drying the resin using warm air. This reduces the density to approximately 30 lbs/cu. ft. The drying process, thus, reduces the overall weight of a batch of the resin by approximately 35%. 
   As an example of suitable dimensions, an ET 718 cartridge is approximately 18″ long, 7.5″ outside diameter, 2 3/32″ to 3½″ inside diameter at the gasket  24 , and weighs approximately 20 lbs when dry. An ET 119 cartridge is approximately 19″ long and 11″ in diameter, with a 2 3/32″ diameter inner cage, and contains about 1 cubic foot of ion exchange resin. When a cartridge as shown in  FIG. 1  is charged with Hilite E ion exchange resin, a liner  32  of tubular polyester material having an unstretched diameter of approximately 4⅝″ to 5¾″ may be suitable. 
   Referring now to  FIG. 3 , a second embodiment of the cartridge according to the invention is shown and generally indicated by the reference numeral  40 . This cartridge  40  is similar to the cartridge  10  shown in  FIGS. 1 and 2 , except that a retaining band  44  extends inside the liner  42  almost the entire length of the liner. As a result, the liner adopts a largely tubular configuration, with only short end regions that are unsupported by the retaining band  44 . These ends spread out to wrap over the ends of the outer cage  14 . 
   The assembly and use of the cartridge  40  shown in  FIG. 3  are similar to those of the cartridge  10  shown in  FIGS. 1 and 2 . However, when the ion exchange resin  16  swells the sleeve  42  and retaining band  44  expand along their entire length. Consequently, the entire space  46  between the sleeve  42  and the outer cage  14  is fully available for expansion. As shown in  FIG. 3 , this allows an expansion space  46  that is narrower radially than the middle part of the expansion space  36  in  FIG. 1 , for the same expansion of the ion exchange resin  16 . 
   As with the embodiment shown in  FIGS. 1 and 2 , instead of using a retaining band, the liner may be formed with different or denser knitting in the region where the retaining band is shown in  FIG. 3 . 
   Referring now to  FIG. 4 , a third embodiment of the cartridge is shown and generally indicated by the reference numeral  50 . This cartridge is similar to the cartridge  10  shown in  FIG. 1 , except that there is no retaining band  34 . Instead, the liner  52  is separated from the outer cage  14  by two spacer rings  54  to form an expansion space  56 . The spacer rings  54  each consist of an annular disk with an axial flange  58  at the inner edge which rests against the liner  52 . The flange  58  of the spacer ring  54  is designed to inhibit expansion of the liner  52 . The free end of the flange  58  may be angled radially outward, so that the liner  52  does not contact the edge and tear. Alternately the free edge of the flange  58  may be carefully smoothed and rounded. The spacer rings  54  may be fixed to the outer cage  14  in any appropriate way. 
   The use of two spacer rings  54 , instead of a single retaining band  34  permits the liner  52  to stretch, and the ion exchange resin  16  to expand outwards, between the spacer rings as well as outside them. 
   Although specific embodiments of the invention have been described, various modifications are possible. In particular, although three embodiments have been described, those skilled in the art will understand how parts and features from different embodiments may be combined to produce a variety of permutations. 
   It is also contemplated that the present invention can be modified to include a sensor which detects and indicates when the cartridge is substantially filled. For example, a sensor could be incorporated which includes contacts on the liner and the outer cage such that when the liner expands and the contacts touch, a light or other indicator is activated. It is also contemplated that one or both ends of the cartridge could include a removable access lid that permits removal and replacement of the resin. 
   The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.