Patent Publication Number: US-7216673-B2

Title: Non-metallic expansion tank with internal diaphragm and clamping device for same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of priority from U.S. provisional application No. 60/570,733, which was filed on May 12, 2004, the disclosure of which is hereby incorporated by reference in its entirety. 

   FIELD OF INVENTION 
   The present invention relates to water systems, e.g., closed hot water heating systems, pressurized water systems, and the like, that include expansion tanks or well tanks and, more particularly, to water systems including non-metallic expansion tanks with an internal diaphragm that separate air cells from water cells. 
   DESCRIPTION OF THE RELATED ART 
   Water systems that provide and distribute well water domestically in rural parts of the country typically include a pump to draw water from the well; pipes or other conduits through which water travels; and a tank for storing water, e.g., a well tank. Well tanks, e.g., expansion tanks, are structured and arranged to store water until demanded and to accommodate internal pressures of the system. To this end, well tanks typically provide an air cushion for the supply water. 
   Generally, the water chamber in the interior of the tank assembly that stores water is in fluid communication with the pipes or conduits of the domestic water system. By design, the water chamber is structured and arranged to provide an operating pressure, e.g., about 20 to 40 pounds per square inch (“psi”), to the water system. To accomplish this, the compressible gas chamber contains a pressurized gas, e.g., nitrogen or, more preferably, air, that can force water through the water system and that, further, can prevent creation of negative, or back pressures in the water system during the cyclical demand for water and/or volume changes associated with the change in water temperature. If the pressure in the water chamber falls below the operating pressure, the pump is activated and water is added to the water chamber of the expansion tank until the water chamber again provides the operating pressure. 
   In any closed system containing air and water that undergoes natural or artificial temperature changes, the likelihood of problems stemming from interaction of air and water is great. Air is soluble in water and water readily absorbs air. Indeed, the amount of absorbed air in water is inversely proportional to the water temperature. Thus, as water is heated, e.g., in connection with a closed hot water heating system, the air in the water is liberated into the system and as heated water cools, the cooling heated water in direct contact with air, e.g., in the compression tank, absorbs some of the free air. By its very nature and through thermal circulation, air-charged water that is cyclically heated and cooled changes continually so that during the next heating cycle the re-absorbed air is again liberated into the system. This cyclical and reversible process is repeated as often as the heating, or firing, cycle is repeated and the boiler water is heated and cooled. This poses many problems to designers. 
   First, air released by heated water, typically, accumulates in the compression tank and other portions of the heating system. This accumulation results in reduced heating efficiency, often making continuous venting of radiators or convectors to bleed off the air necessary. Moreover, as water is heated, it can expand into the compression tank that is connected to the pipes and other conduits. Typically, in the compression tank, the expanding, heated water is in intimate communication with the released air and any other air in the tank. However, when the heated water reaches a desired temperature, the firing of the boiler ceases and the water begins to cool and contract. As the water cools, it re-adsorbs free air in the compression tank. 
   Second, when a tank includes an air cushion, the cooling water may absorb all or substantially all of the air cushion, leaving a static water system. Without an air cushion, or, more specifically, air pressure to force water through the system, a pressure pump may be needed constantly. Optionally, an air surge chamber can be provided that is not in direct contact with the water, thereby eliminating the need of the pressure pump operating every time a faucet was turned on. Pressure pumps and surge chambers increase the cost of a water system. 
   To address these shortcomings, conventional expansion and well tanks (collectively “tank assemblies”) typically include impermeable diaphragms, or bladders, to separate the interior of the well tank into two chambers, or cells: a liquid, or water, chamber and a compressible, or pressurized, gas chamber. As water is pumped from a well into the tank assembly, the volume of the water in the water chamber increases, causing the diaphragm to contract the volume of the pressurized gas chamber. As the volume of the pressurized gas chamber decreases, the gas pressure in the pressurized gas chamber increases. As a result, when water for the tank is demanded by the water system, the gas in the pressurized gas chamber forces the water into the water system. Consequently, the volume of water in the water chamber decreases and the volume of the pressurized gas chamber increases. As a result, the pressure of the pressurized gas decreases. 
   Conventional diaphragms are constructed of a non-porous, elastic material, e.g., plastic or butyl rubber, and are sealed at the periphery or sidewall of the tank to provide an air- and watertight seal. Not only does use of a diaphragm avoid the above-described air-water problems, but, also, separation of water from the pressurized gas is desirable because water in the presence of oxygen produces oxidation that can damage metal or other portions of the system and, furthermore, can aerate the water, which can affect water quality. 
   An example of a conventional tank assembly is provided in commonly assigned U.S. Pat. No. 5,386,925 to Lane. The Lane patent provides an expansion tank comprising a deformable diaphragm that divides the tank into two sections. The diaphragm separates the gas in the one section of the tank from the water in the other section of the tank and the rest of the system. The gas section is pre-charged with gas under pressure so that the diaphragm is displaced to increase or decrease the volume of this section according to the variations of the volume of water in the other section. 
   The Lane expansion tank system includes two sections that are made of metal, which requires assembly with, i.e., welding to, a metal clamp ring that is disposed inside of the two tank portions. This assembly is relatively expensive and labor and time intensive to manufacture. Moreover, steel tanks can corrode from external environmental exposure, which can lead to deterioration of the tank assembly and the water system. Such deterioration can lead to catastrophic results, such as leaking tanks. 
   To provide some protection from corrosion, the inner surface of the liquid chamber portion of the metal expansion tank is covered by a water, or liquid impervious liner. This, however, requires fabricating the liner in a separate operation and then inserting the liner in the liquid chamber portion. 
   Therefore, it would be desirable to provide a non-metallic tank assembly that does not affect the quality or taste of the water or that does not deteriorate over time in a corrosive environment. It would also be desirable to provide a non-metallic tank assembly with an internal diaphragm interposed between the water chamber and the gas chamber to separate the water from pressurized gas. Furthermore, it would be desirable to provide a non-metallic, diaphragm-type tank assembly that can withstand the internal pressures normally associated with tank assemblies. Finally, it would be desirable to provide a lighter, non-metallic alternative to conventional metallic tank assemblies and to provide such a tank at lower cost. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a non-metallic, diaphragm-type tank assembly for use in combination with a well, potable water supply or non-potable water supply. 
   It is another object of the present invention to provide a lightweight, diaphragm-type tank assembly that is more economical to purchase and to maintain and that has a longer life than conventional metallic alternative tanks. 
   It is yet another object of the present invention to provide a diaphragm-type tank assembly that is more resistant in a corrosive environment than conventional metallic alternative tanks. 
   The present invention attains the foregoing and additional objects by providing a non-metallic, diaphragm-type tank assembly for use with a pressurized water system, the tank assembly comprising a non-metallic outer body; a non-metallic inner shell assembly, including an upper portion and a lower portion, that is contained by the non-metallic outer body; and a diaphragm that is structured and arranged about the upper and lower portions of the inner shell assembly to separate said inner shell assembly into a water portion and a pressurized gas portion. 
   Preferably, the non-metallic outer body is manufactured from wound fiber strands impregnated with a resin matrix, e.g., an epoxy resin or a thermoplastic resin, in a substantially cylindrical shape and, more preferably, the non-metallic outer body is formed as a single piece by at least one of the following manufacturing methods: injection molding, extrusion, blow molding, and roto-molding. 
   In a preferred embodiment, the non-metallic inner body is manufactured from a thermoplastic, e.g., by molding or extrusion, and the upper and lower portions of the non-metallic inner shell assembly are substantially dome shaped. Preferably, the upper portion of the non-metallic inner body has a first overlapable end portion and the lower portion of the non-metallic inner body has a second overlapable end portion, and the first overlapable end portion is secured to the lower portion to provide an airtight pressurized gas portion in the upper portion of the non-metallic inner shell assembly. 
   In one aspect of the present invention, the first overlapable end portion of the upper portion is adhesively secured to the lower portion. In another aspect of the present invention, the first overlapable end portion of the upper portion is secured to the lower portion by spin welding. In still another aspect of the present invention, the first overlapable end portion of the upper portion is secured to the lower portion by heat sealing. Optionally, the lower portion is provided with a ledge to which the first overlapable end portion can be fixedly or adhesively attached. 
   Preferably, the diaphragm comprises a resilient, non-porous material and/or an elastomeric material selected from a group comprising rubber, butyl rubber, thermoplastic, and elastomer plastic. More preferably, the diaphragm includes a bead portion comprising an annular ring that is convex on an inner side and concave on an outer side at its outer periphery. As a result, the bead portion of the diaphragm can be removably secured to the overlapable second end portion of the lower portion of the inner shell assembly to provide a watertight water portion in the lower portion. 
   In one aspect of the present invention, the bead portion is removably secured to the overlapable end portion of the lower portion of the inner shell assembly by a clamping system that comprises an inner clamp hoop and an outer band. Specifically, the outer band can be mechanically crimped to compress and secure the second overlapable end portion and the bead portion of the diaphragm between the inner clamp hoop and the outer band to provide a watertight water portion. 
   In a second embodiment, the present invention discloses a clamping assembly for securing an elastomeric diaphragm to the sidewall of a lower portion of an inner shell assembly to provide a watertight water portion and an airtight pressurized gas portion in the inner shell assembly of the water tank assembly. Preferably, the clamping assembly comprises an outer or external band that is mechanically crimped to provide an external hoop stress and an inner clamp hoop that provides a resisting hoop stress. More preferably, the external band is mechanically crimped to provide an external hoop stress that securely pinches the second overlapable end of the lower portion of the inner shell assembly and a beaded end of the diaphragm against the resisting hoop stress of the inner clamp hoop. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     For a fuller understanding of the nature and desired objects of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawing figures wherein like reference characters and numerals denote corresponding parts throughout the several views and wherein: 
       FIG. 1  is a diagram of an illustrative embodiment of a diaphragm-type tank assembly of the present invention; 
       FIG. 2  is a diagram of an illustrative embodiment of a diaphragm clamping assembly in accordance with the present invention; 
       FIG. 3  is a diagram of an illustrative embodiment of the upper dome portion and diaphragm clamping assembly in accordance with the present invention; and 
       FIG. 4  is a diagram of an illustrative embodiment of a diaphragm clamping assembly in which water pressure has displaced the diaphragm into the pressurized gas chamber. 
   

   DETAILED DESCRIPTION OF INVENTION AND ITS PREFERRED EMBODIMENT 
   Referring now to the various figures of the drawings, wherein like reference characters refer to like parts, there is shown in  FIGS. 1 and 2  an embodiment of a diaphragm-type tank assembly  10  in accordance with the present invention. The tank assembly  10  comprises an outer cylindrical housing or body  12  and an inner shell  14 . The outer cylindrical body  12  is structured and arranged of a non-metallic material to provide structure and to protect the inner shell  14 . The inner shell  14  is structured and arranged of a non-porous, non-metallic material, e.g., plastic, to provide a watertight water cell  18 , or chamber, and an airtight pressurized gas cell  16 , or chamber. A heavy gauge, non-porous, elastomeric diaphragm  20  is structured and arranged within the inner shell  14  to separate the water cell  18  and the pressurized gas cell  16 . 
   Preferably, the outer cylindrical body  12  of the tank assembly  10  is made of fiber strands impregnated with a resin, e.g., an epoxy or thermoplastic resin. The fiber strands are preferably woven filaments, e.g., carbonaceous fibers, fiberglass, aramid fibers (Kevlar®), and the like. The cylindrical body  12  provides structural support to the tank assembly  10  and is capable of withstanding normal operating pressures associated with domestic water systems, e.g., 0 to about 100 psi. The cylindrical body  12  can be formed, e.g., by injection molding, extrusion, blow molding, rotomolding, and the like, to form a single piece. 
   The cylindrical body  12  of the tank assembly  10  includes openings and appurtenant connections that are normally associated with conventional tank assemblies. For example, the lower portion  15  of the cylindrical body  12  can include connections (not shown) or other means for providing fluid communication between the tank assembly  10  and the water distribution pipes or conduits. In addition to the connections, the cylindrical body  12  can include one or more drain-cock valves  11  for draining or bleeding water from the water cell  18 . The connections in the cylindrical body  12  are structured and arranged to be in registration with similar connections (not shown) in the water cell  18  of the inner shell  14 , which are described in greater detail below. 
   Similarly, the upper portion  13  of the cylindrical body  10  can include the necessary connections (not shown) or other means for providing fluid communication between the pressurized gas cell  16  and the ambient atmosphere. For example, these connections can include a pressure release valve (not shown), which extends through the cylindrical body  12  and the inner shell  14 , to bleed off gas pressure in the pressurized gas cell  16  and/or to introduce more gas into the pressurized gas cell  16 . 
   Preferably, the diaphragm  20  is made of a resilient, non-porous, elastomeric material, e.g., elastomer plastic, thermoplastic, rubber, butyl rubber, and the like, that can produce an air- and watertight seal between the two cells  16  and  18 ; that can withstand normal operating pressures associated with domestic water systems; that does not de-ionize or deteriorate in the presence of water and/or ions generally contained in water; and that is responsive to changes in volume of the water in the water cell  18  and to changes in pressure of the gas in the pressurized gas cell  16 . 
   In a preferred embodiment, the diaphragm  20  includes a peripheral, or bead portion  25  at its outer perimeter. Preferably, the bead portion  25  is structured and arranged as an annular ring that is convex on its inner side  25   a  and concave on its outer side  25   b . The diaphragm  20  is sealed at the sidewall of the inner shell  14  and, further, structured and arranged to provide airtight and watertight seals in the pressurized gas cell  16  and in the water cell  18 , respectively. 
   Referring to  FIG. 3 , in a preferred embodiment, the inner shell  14  comprises an upper dome portion  17  and a lower dome portion  19  that have been molded or extruded individually. Preferably, the dome portions  17  and  19  include overlapable, free peripheral end portions  17   a  and  19   a,  respectively, that permit the peripheral end portion  17   a  of the upper dome portion  17  to mate with the lower dome portion  19 . Similar to the cylindrical body  12 , the inner shell  14  of the tank assembly  10  also includes connections and conduits (not shown) that are normally associated with conventional tank assemblies. The connections and conduits are further disposed in registration with similar connections and conduits in the cylindrical body  12 . 
   For example, the lower dome portion  19  of the inner shell  14  can include connections (not shown) for providing fluid communication between the water cell  18  of the tank assembly  10  and the pipes or conduits of the water distribution system and/or drain-cock valves  11  for draining or bleeding water of other fluids from the water cell  18 . Similarly, the upper dome portion  17  of the inner shell  14  can include a pressure release valve (not shown) that is in fluid communication with the ambient atmosphere through the cylindrical body  12  to bleed off gas pressure in the pressurized gas cell  16  and/or a connection for introducing more gas into the pressurized gas cell  16 . 
   A preferred method of securing the diaphragm  20  at the sidewall of the end portion  19   a  of the lower dome portion  19  to provide a water chamber  18  will now be described. Referring to  FIGS. 2 and 4 , the bead  25  of the diaphragm  20  and the end portion  19   a  of the lower dome portion  19  of the inner shell  14  are shown sandwiched, i.e., clamped or pinched, between an inner clamp hoop  22  and an outer or external band  24 . From the innermost diameter of the tank assembly  10 , the clamping assembly includes the inner clamp hoop  22 , the bead  25  of the diaphragm  20 , the overlapped end portion  19   a  of the lower dome portion  19 , and the outer band  24 . 
   Preferably, the inner clamp hoop  22  comprises a grooved metal ring, e.g., a steel ring, that has been pre-fabricated to be substantially convex at its inner diameter and substantially concave at its outer diameter to provide a grooved portion  26 . 
   In a preferred embodiment, the outer band  24  comprises a metal ring, e.g., a steel ring, that is mechanically crimped during assembly to provide a complementary groove that is substantially convex at its inner diameter and substantially concave at its outer diameter. In one aspect of the present invention, the inner, convex side  25   a  of the bead  25  of the diaphragm  20  is in intimate contact with the grooved portion  26  of the inner clamp hoop  22  and the outer, concave side  25   b  of the bead  25  of the diaphragm  20  is in intimate contact with the end portion  19   a  of the lower dome portion  19 . The end portion  19   a  of the lower dome portion  19  is in intimate contact with the outer band  24 . 
   The length of the overlapped portion  19   a  of the lower dome portion  19  should be of sufficient length to provide an acceptable factor of safety against slippage due to the operating pressures of the tank assembly  10  to prevent such slippage from affecting the integrity of air- and watertight seals. 
   Once the bead  25  of the diaphragm  20  and the overlapped end portion  19   a  of the lower dome portion  19  have been disposed in proximity of the groove  26  of the inner clamp hoop  22  and the outer band  24  has been disposed concentrically and coaxially about the inner clamp hoop  22  with the bead  25  of the diaphragm  20  and the overlapped end portion  19   a  of the lower dome portion  19  disposed between the inner clamp hoop  22  and the outer band  24 , the entire assembly can be crimped or pinched together, e.g., using a crimping tool such as a mechanical crimper. Preferably, the crimping tool, e.g., mechanical crimper, can travel around the periphery of the assembled device, exerting a force around the periphery of the outer band  24  to provide a groove in the outer band  24  that is in registration with the groove  26  of the inner clamp hoop  22 . 
   The effect of the crimping or pinching is that the inner clamp hoop  22  produces and exerts a radial, or hoop stress against the closely clamped, i.e., pinched, overlapped end portion  19   a  of the lower dome portion  19  of the inner shell  14 , the bead  25  of the diaphragm  20 , and the outer band  24 . The grooved portion of the outer band  24  is structured and arranged to provide and exert a resisting hoop stress to retain the pinched or crimped overlapped end portion  19   a  of the lower dome portion  19  of the inner shell  14  and the bead  25  of the diaphragm  20 . The diaphragm assembly that is produced does not expose any metal in the water cell  18  of the inner liner  14 . 
   Once the clamping assembly has been crimped, portions of the outer band  24  that do not provide hoop stress resistance can be removed (not shown). Alternatively, as shown in  FIG. 3 , an upper portion of the outer band  24  can be mechanically formed to pass over the upper portion of the bead  25  of the diaphragm  20  and the overlapped end portion  19   a  of the lower dome portion  19 . 
   A preferred method of securing the upper dome portion  17  to the assembled lower dome portion  19  and aforementioned diaphragm clamping assembly to provide a pressurized gas cell  16  and to complete the inner shell  14  of the tank assembly  10  will now be described. Referring to  FIG. 3 , there are shown the previously described diaphragm clamping assembly and the overlapped end portion  17   a  of the upper dome portion  17 . Preferably, the overlapped end portion  17   a  of the upper dome portion  17  can be secured to a shoulder portion  19   b  that is pre-formed in the lower dome portion  19  for that purpose. More preferably, only the tip  17   b  of the upper dome portion  17  is secured to the shoulder portion  19   b  of the lower dome portion  19 . Means of securing the tip  17   b  to the shoulder portion  19   b  include, without limitation, adhesively, by spin welding, by heat-sealing, and the like. However, the invention is not to be construed as being so limited. 
   With this arrangement, gas in the pressurized gas cell  16  and water in the water cell  18  can be confined between the diaphragm  20  and, respectively, the upper dome portion  17  of the inner shell  14  and the lower dome portion  19  of the inner shell  14  to provide airtight and watertight environments. Moreover, in one aspect of the present invention, the diaphragm  20 , as it displaces as a function of water volume and/or gas pressure, is able to displace within the inner circumference of the inner hoop  22 . Further, as the water volume increases, the diaphragm  20  displaces into the pressurized gas cell  16  in such a manner so as to cover the inner hoop  22  and prevent water from contacting the inner clamp hoop  22 . The outer shell  12  can be then be placed about the assembled inner shell  14  in a manner that is well known to those of ordinary skill in the art to complete the tank assembly  10 . 
   Although a preferred embodiment of the invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.