Abstract:
A bi-directional filter has a pair of flapper-type check valve assemblies 20, 21 for directing fluid flow unidirectionally through a centrally supported molded desiccant core 22. Each check valve assembly is a three part structure spot-welded into a unitary assembly having a centering support plate, a core support cup and an intermediate flapper valve plate. A depth-type filter media circumferentially surrounds the desiccant core and extends between the check valve assembly on either end of the core for providing filtering for the fluid prior to entering the molded desiccant core. A depth-type filter media 80, 81 is also provided at each axial end of the core for providing fine filtration of the fluid after the fluid has passed through the core. The outer filter media is arranged to allow a portion of fluid therein to bypass the desiccant core.

Description:
This application claims the benefit of U.S. Provisional Application No. 60/039,846 filing date Mar. 20, 1997. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to filter driers and more particularly to a bidirectional flow filter drier which is especially useful in heat pump systems or any other air conditioning or refrigerant systems where fluid flows may be reversed. 
     Bidirectional flow filter drier assemblies are well-known in these fields and provide convenient, economical devices which utilize a common filter drier medium and a minimum of interconnections with the plumbing of the system which is advantageous both from the standpoints of minimal original equipment and ease of maintenance and repair. 
     One particularly useful biflow drier is shown in Griffin, U.S. Pat. No. 4,954,252, which is owned by the assignee of the present invention. In the Griffin drier, a simplified and reliable biflow filter drier structure is provided which utilizes a minimal number of components. A valving structure in the filter drier is easily fabricated from punched metal parts and readily assembled by spot welding techniques. The valving structure includes a pair of identical check valve assemblies and a single molded desiccant core. The check valve assemblies are located at opposite ends of the core and each includes stainless steel reed-type flapper valves formed from a single sheet of material. While the Griffin drier structure is appropriate for many applications, the desiccant core provides both filtration and water removal functions, which can reduce the operational life of the desiccant. The desiccant in the core has small openings which can plug or clog, particularly on the surface of the core, and which may require frequent drier replacement. 
     As such, it is believed that there is a demand for a further improved bidirectional flow filter drier which has a structure where the desiccant core is not required to provide a filtration function, but which rather performs primarily a water-removing function and which thereby extends the useful life of the filter drier. 
     SUMMARY OF THE INVENTION 
     A new and unique bidirectional flow filter drier is provided where a depth-type filter media layer surrounds the desiccant core in the housing of the drier. The filter media layer extends against and along the outer surface of the desiccant core, preferably in one or more rings extending circumferentially around the core. The outer filter preferably has a greater filtration efficiency than the desiccant core to remove particles before the particles enter the core. The depth type of media for the outer filter captures the particles throughout substantially the entire thickness of the media, which extends the operational life of the desiccant material. 
     An additional filter media layer can be provided at both ends of the desiccant core. The end filters are disc-shaped and are disposed between the end surface of the core and the valve assembly associated with the end surface. The end filters separate fine particles from the fluid exiting axially from the core (depending upon the direction of fluid flow) and prevent the particles from being returned to the fluid system. A portion of the fluid passing through the drier can also pass directly from the outer filter to the end filters and bypass the desiccant core. 
     The filter drier includes a tubular housing, a pair of end caps with flow port fittings at either end of the housing, and a pair of identical check valve assemblies supporting opposite ends of the desiccant core. Each check valve assembly is preferably a spot-welded structure of a centering plate, a core support cup, and an intermediate flapper valve plate. The valve plate includes a pair of flapper reeds extending in opposite directions from a central support surface and normally covering a central valve opening in the core support cup, and at least one offset opening in the centering plate. The valves plates are moved to open positions by fluid pressure and are prevented from overtravel and overstressing by stop surfaces on both the core support cup and the centering plate. The flapper valve plates are formed from a single thin sheet of metal, preferably stainless steel. 
     A screen is provided against the outer end surface of each of the end filters to support the end filters. Perforated plates can also be provided against each of the inner and outer end surfaces of the end filters to support the end filters. The perforated plates on the inner end surface of the end filters also support the ends of the desiccant core and the ends of the outer filter. The brass screen and perforated plates are disposed within and supported by the core support cup in the check valve assemblies. 
     Further features of the present invention will become apparent to those skilled in the art upon reviewing the following specification and attached drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of the filter drier of the invention showing the valves therein in a reverse flow condition; 
     FIG. 2 is a sectional view of the filter drier of the invention showing the valves therein in a forward flow condition; 
     FIG. 3 is an end view of one of the flapper valve assemblies; 
     FIG. 4 is a sectional view of the flapper valve assembly of FIG. 3, taken along the lines  4 — 4 ; 
     FIG. 5 is an end view of the core support cup forming one part of the flapper valve assembly; 
     FIG. 6 is a sectional view of the core support cup of FIG. 5, taken along the lines  6 — 6 ; 
     FIG. 7 is a plan view of the flapper valve portion of the flapper valve assembly; 
     FIG. 8 is a plan view of a perforated plate supported at either end of the desiccant core; 
     FIG. 9 is an enlarged sectional view of the flapper valve assembly shown in FIG. 4; 
     FIG. 10 is a sectional view of a filter drier constructed according to an additional embodiment of the present invention; 
     FIG. 11 is a plan view of one of the perforated plates supported at one end surface of the end filters for the filter drier of FIG. 10; 
     FIG. 12 is a sectional view of the core support cup forming one part of the flapper valve assembly for the filter drier of FIG. 10; and 
     FIG. 13 is a plan view of another of the perforated plates supported at another end surface of the end filters for the filter drier of FIG.  10 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIGS. 1 and 2 there is shown a first embodiment of the filter drier  10  of the invention in the operating modes of reverse fluid flow in FIG.  1  and forward fluid flow as depicted in FIG. 2, for a conventional heat pump system or the like. The filter drier  10  comprises a tubular casing  11  having first and second ends at which end caps  12 ,  14  are positioned. End caps  12 ,  14  are closure members for tubular casing  11  and each respectively includes a fluid flow port  15 ,  16 . In this embodiment of the invention, the fluid flow ports  15 ,  16  are depicted as short tubular stubs centrally positioned in end caps  12 ,  14  and located substantially on the central axis of casing  11 . End cap  12 ,  14  and flow ports  15 ,  16  may comprise separate structures but typically are brazed or welded to one another and to casing  11  to form an integral housing structure. Flow ports  15 ,  16  may be joined to interconnecting conduits of a typical heat pump system by a soldered connection or by another convenient joining technique. 
     Located within casing  11  are first and second valve assemblies  20 ,  21  and porous molded desiccant core  22  which is supported between valve assemblies  20 ,  21 . Molded desiccant core  22  is a rigid, but porous cylindrical structure having a central longitudinal bore  24  therein with slightly outwardly flared ends, although the desiccant core  22  could also be a solid structure without such a bore to maximize the quantity of desiccant material available (see, e.g., FIG.  10 ). In any case, the desiccant core is is preferably formed of activated alumina and molecular sieve with a phosphate bond or an organic bond (such as a polyphenylene sulfide), although many other materials would be suitable. Core  22  includes an outer peripheral cylindrical surface  25  and is adapted in this embodiment of the invention for unidirectional fluid flow through core  22  from outer surface  25  to central bore  24 . 
     An outer porous filter media layer  26  surrounds desiccant core  22 . Outer filter  26  is preferably a depth type of media, such as a non-compressed layer of fiberglass or polyester, and is preferably formed in a ring, donut or annulus, the inner surface of which is located in contact with the outer surface of the desiccant core. Outer filter  26  can be a single ring, or a series of rings in adjacent abutting contact along the desiccant core. The ring(s) extend along at least a portion of the desiccant core between the two valve assemblies  20 ,  21 , and are supported and retained therebetween. The thickness of this outer filter media layer is on the order of 0.4 inches for a desiccant core having a radial diameter on the order of 1.5 inches, but can vary and depends upon the space between the inside surface of casing  11  and desiccant core  22 , the efficiency and required life of the media, and the cost of the media. Generally, the thicker the media layer the longer the useful life of the desiccant material. However, the media layer should not be so thick as to block or substantially restrict fluid flowing around the periphery of the desiccant core. 
     Outer filter  26  is chosen so as to filter out substantially all particulate matter passing radially inward through the desiccant core  22  which would normally clog the pores in the desiccant core and reduce the effectiveness of the desiccant media. The outer filter  26  should therefore provide at least the same and preferably slightly finer filtration (be slightly more efficient) than the desiccant material. By using an outer filter, a larger pore size can be used with the desiccant core, which allows less expensive desiccant material (such as molecular sieve) can be used, thereby reducing the cost of the desiccant core and the overall cost of the filter drier; and increase the flow through the drier, which increases the efficiency of the system. It is believed that the depth type of media for the outer filter  26  allows for increased contaminant removal as compared to a surface-type of media, as a depth-type of media generally collects particles throughout substantially its entire depth while a surface type of media, as the name suggests, only collects particles on its outer surface. However, although not preferred, a surface-type of media could also be used to obtain some of the benefits of the present invention. 
     Each valve assembly  20 ,  21  is identical but positioned reversely in casing  11  to direct fluid flow in the manner depicted by arrows in FIGS. 1 and 2. Only valve assembly  21  will be described in detail and it will be understood that valve assembly  20  comprises an identical construction. Referring more particularly to the enlarged view of FIG. 9 it will be seen that valve assembly  21  comprises only three components consisting of centering support plate  30 , core support cup  31  and flapper valve plate  32 . In the view of FIG. 9 valve assembly  21  is shown in the assembled, normally closed condition, while in FIGS. 1 and 2, valve assemblies  20 ,  21  are shown as subject to fluid flow. 
     With reference also to FIGS. 3 and 4, centering support plate  30  consists of a circular disk shaped member having a flat bottom wall  35 , cylindrical peripheral side wall  36  and outwardly directed annular flange  38 . Support plate  30  is formed as a simple stamping, typically of steel and may be formed of sheet material on the order of 0.024 inch thickness, and having an overall diameter on the order of 2.5 or 3.0 inches. Support plate  30  further includes a generally circular central opening  40  which is formed by punching and partially severing a flap  41  of material which is left angled with respect to the plane of bottom wall  35  at an angle of approximately twenty-five degrees. As will be described in greater detail hereafter, flap  41  serves as an overtravel stop for one of the check valves of valve assembly  21 . A further offset passage  44  is provided in bottom wall  35  of support plate  30 , being positioned about midway between central opening  40  and side wall  36 . The periphery of offset passage  44  is the valve seat for one of the check valves of valve assembly  21 . The passage  44  may be a single circular opening, a slotted opening, or a plurality of openings. 
     With reference as well to FIGS. 5 and 6, core support cup  31  is a circular cup-shaped member having a central flat bottom wall  48 , conical intermediate wall  49 , flat annular shelf  50  and cylindrical outer wall  51 . Support cup  31  further includes a central circular opening  54  in bottom wall  48 , the periphery of which is a valve seat for one of the check valves of valve assembly  21 . Conical wall  49  is angled relative to bottom wall  48  at an angle of about twenty-eight degrees and serves as the overtravel stop for one of the check valves of valve assembly  21 . Core support cup  31  is also formed of thin steel sheet on the order of 0.024 inch thickness. 
     Valve assembly  21  is completed by flapper valve plate  32  which also is a thin plate and which is sandwiched between support plate  30  and support cup  31 . With reference also to FIG. 7, flapper valve plate  32  is preferably a stainless steel, sheet metal stamping, on the order of 0.003 inch thickness and consists essentially of first flapper valve  60 , second flapper valve  61 , and intermediate support section  62 . Flapper valves  60 ,  61  extend in opposite directions from central support section  62  in the form of reed valves and in this embodiment of the invention have generally circular distal ends sized to adequately cover the associated valve seat openings, although the configuration of the flapper valves can very depending upon the configuration of the corresponding valve seat opening. As best seen in FIG. 9, first flapper valve  60  is disposed adjacent opening  54  of support cup  31 , and second flapper valve  61  is disposed adjacent offset opening  44  of support plate  30 . Flapper plate  32  further comprises annular support section  65  which is an extension of intermediate support section  62  and which surrounds first flapper valve  60 . Annular support section  65  includes three holes  68  spaced at ninety degree intervals, which receive weld projections for securing support plate  30  and support cup  31  by spot welds. Flapper valve plate  32  court be formed of other materials as well, such as Teflon® or the like, and the entire assembly joined by staking rather than spot welds, which would avoid heat distortion effects. 
     With support section  62  and annular support section  65  in firm engagement therebetween, support plate  30  and the bottom wall  48  of support cup  31  are positioned in substantially parallel, close engagement with flapper valves  60 ,  61  covering the respective valve seat openings  54 ,  44 , thereby forming a pair of check valves. Since the material of flapper valve plate  32  is thin and flexible, flapper valves  60 ,  61  are able to flex away from their respective valve seat openings  54 ,  44  under the urging of fluid flow to allow flow in one direction, but to prevent flow in the opposite direction when the valves are urged against their respective valve seats. Flapper valve  60  may be moved to an open position away from opening  54  but is limited from over-flexing by overtravel stop  41 . Similarly, flapper valve  61  may be moved to an open position away from opening  44  but is limited from overflexing by conical wall  49  of support cup  31 , both conditions being depicted in FIGS. 1 and 2. In this embodiment of the invention, central valve seat opening  54  is on the order of 0.5 or 0.6 inch diameter, while offset valve seat opening  44  is on the order of 0.375 or 0.5 inch diameter. 
     The valve assemblies  20 ,  21  thus comprise rigid support members, each with a pair of check valves therein and are supported in casing  11  by the placement of flanges  38  between the ends of casing  11  and respective end caps  12 ,  14  and permanently securing the structure by brazing end caps  12 ,  14  to casing  11 . Supported in the facing support cups  31  of the valve assemblies  20 ,  21  is molded desiccant core  22  which includes at either end an annular ceramic gasket  70  and circular perforated plate  71 . Perforated plate  71  is seen in plan view in FIG. 8 as comprising a disk having a plurality of apertures  74  at the center thereof and which together with gasket  70  prevents flow of fluid through the ends of core  22 , and allows flow through center bore  24 . 
     Thus, with reference to FIG. 1 it may be seen that under reverse flow conditions, that is, where fluid pressure is higher at port  16  than at port  15 , flow would occur as depicted by the arrows through the offset valve seat  44  of valve assembly  21  and around the periphery of the desiccant core  22 , radially-inward through outer filter  26 , radially-inward through desiccant core  22 , and axially outward through central bore  24  to the center valve seat  56  of valve assembly  20  and port  15 . Under these conditions, the center valve seat  54  of valve assembly  21  and the offset valve seat  58  of valve assembly  20  would be in the normally closed condition and would be further urged to the closed condition by the fluid flow. The outer filter media layer  26  removes harmful particles, which allows desiccant core  22  to function primarily as a water-removing device, rather than also as a filtering device. 
     In the forward flow direction as seen by the arrows in FIG. 2, flow enters port  15 , then passes through the offset valve seat  58  of valve assembly  20 , around the periphery of the desiccant core  22 , radially-inward through outer filter  26 , radially-inward through the desiccant core  22 , and axially outward through central bore  24  to the center valve seat  54  of valve assembly  21  and port  16 . Under these conditions, the center valve seat  56  of valve assembly  20  and the offset valve seat  44  of valve assembly  21  would be closed and firmly urged to the closed position by the fluid flow. Again, outer filter media layer  26  filters the fluid before the fluid enters the desiccant core. In both the forward and reverse flow situations, fluid flows through desiccant core  22  so that the desiccant material may remove water in both directions. 
     In a further embodiment of the invention as illustrated in FIGS. 10-13, the filter drier  10  can include a porous filter media layer  80 ,  81  at either axial end of desiccant core  22 . In this embodiment, each end filter  80 , 81  comprises a disc-shaped media layer for fine filtration of fluid passing out of the desiccant core. The media is preferably a depth-type of media, such as a non-compressed layer of fiberglass or polyester, which collects particles from fluid flowing through the media through substantially its entire depth. The end filters  80 ,  81  have at least the same filtration efficiency and preferably have a finer filtration than the desiccant core  22  and the outer filter  26 , such that the outer filter  26  captures the larger particulate matter to prevent the matter from plugging the pores in the desiccant core, while the smaller particles pass through the outer filter and the desiccant core and are separated by the end filters  80 ,  81  (depending upon the direction of fluid flow). 
     In FIG. 10, the filter drier is shown in a forward flow condition, and fluid passes radially inward through outer filter  26 , radially inward through desiccant core  22 , and then axially outward through end filter  81  to valve assembly  21  and port  16 . For the reverse flow condition, the fluid passes axially outward from core  22  through end filter  80  to valve assembly  20  and port  15 . 
     In this further embodiment, a circular perforated metal plate  84  (FIG. 11) can be located between and against one end surface of desiccant core  22  and the inner (upstream) end surface of end filter  80 , and between and against the other end surface of desiccant core  22  and the inner (upstream) end surface of end filter  81 . Perforated plate  84  has a similar structure as the perforated plate  71  described above with respect to FIGS. 1-9, however, the plate includes apertures  85  formed across the entire plate for directing fluid flowing axially outward from the desiccant core  22 . Plate  84  is also disposed against and supports an end surface of outer filter  26 , and allows a portion of the fluid to bypass desiccant core  22  and flow directly to end filters  80 ,  81  particularly through the perforations which are located between the end surfaces of outer filter  26  and the peripheral portion of the inner end surface of end filters  80 ,  81 . Because the filter drier operates in a closed system, the fluid which flows directly to the end filters and bypasses the desiccant core is likely to pass through the desiccant core in subsequent passes through the filter drier. Additionally, in this case, the portion of the fluid that passes through the desiccant core will travel more slowly than the fluid bypassing the core. The additional contact time enhances moisture removal in the core. Thus the total moisture removal capability of the assembly is essentially unaffected by the partial bypass flow path. 
     Perforated plate  84  is supported within core support cup  89  against a radially-extending annular shoulder  86  formed by outer cup-shaped portion  88  (FIG.  12 ). Cup-shaped portion  88  also receives and retains a portion of the length of outer filter  26 , along both ends of the filter. 
     A circular brass screen  90  is located between and against the outer (downstream) end surface of the end filter  80  and valve assembly  20 , and between and against the outer (downstream) end surface of end filter  81  and valve assembly  21 . Each screen  90  is received and supported by a shoulder  92  formed between the outer cylindrical wall  93  and the conical wall  94  of the core support cup  89  in each valve assembly. Each end filter  80 ,  81  is likewise retained and supported within the outer cylindrical wall  93  between the screen  90  and the perforated plate  84 , and fills the entire length of this wall. Preferably a further circular perforated metal plate  95  (FIG. 13) is located against the outer (downstream) surface of each screen  90  to provide additional support for the outer end surface of end filters  80 ,  81 . Perforated plate  95  can be similar to perforated plate  84 , that is, with openings  96  across the entire plate, and is located between the screen  90  and shoulder  92  within core support cup  89 . 
     All other aspects of the valve assemblies  20 ,  21  and of the outer casing  11  and end caps  12 ,  14  for the filter drier can be the same in this embodiment as in the first embodiment above with respect to FIGS. 1-9. 
     The principles, preferred embodiments and modes of operation of the present invention have been described in the foregoing specification. The invention which is intended to be protected herein should not, however, be construed as limited to the particular form described as it is to be regarded as illustrative rather than restrictive. Variations and changes may be made by those skilled in the art without departing from the scope and spirit of the invention as set forth in the appended claims.