Abstract:
Valveboxes of this invention comprise a housing including an inner chamber that extends axially through the housing from a housing base. The housing chamber includes a diameter that is defined by a housing sidewall surface that extends outwardly from the base, forming a chamber opening. The chamber opening includes a seal surface that is positioned radially inwardly towards the chamber. The valve box further includes a lid that is positioned over the housing chamber opening. The lid includes a concave center section and a seal surface disposed radially therearound. The lid seal surface is positioned radially towards the chamber, and is placed opposite the chamber opening seal surface. An annular seal is interposed between the housing chamber and lid seal surfaces. The chamber and lid seal surfaces are configured generally perpendicular to the chamber opening, such that internal pressure within the chamber causes the concave center portion to impose a radially outwardly directed pressure onto the lid, thereby further compressing the annular seal to ensure a leak-tight seal.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the benefit of provisional application No. 60/254,731, filed on Dec. 11, 2000. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates to an enclosure known within the industry as a valve box. The valve box is used to enclose fluid handling devices, such as a valve and manifold system, for the purpose of containing fluid leaks and, more particularly, specifically designed to provide an improved degree of fluid containment should the system be under pressure.  
         BACKGROUND OF THE INVENTION  
         [0003]    In certain industries caustic chemicals are used in processing stages that necessitate special handling precautions. The special handling precautions implemented depend upon the particular process operation and the type of product being produced. In instances, the special handling precaution can be limited to the selection of materials, making sure that the material selected to build the fluid handling system does not fail when exposed to the process chemicals. In other instances, it is desired that the material selected to form the wetted portion of the fluid handling system not introduce contaminate materials in the process during use, to thereby avoid contaminating an otherwise ultra-pure process. Further, special handling precautions are taken to provide a containment system around a primary fluid handling device that contains the process fluid, to thereby limit its exposure to the environment and minimize any related health risk or environmental impact, should the primary fluid handling device leak or fail.  
           [0004]    In the semiconductor industry, in particular, extremely acidic chemicals are used during the process of making semiconductors. The process of making semiconductors also requires that the processing liquid be of a high purity level, to not contaminate the final product. Therefore, an additional requirement is that the material selected for making the wetted fluid handling device not introduce containment material into the system during processing. Fluorpolymeric tubing is commonly used for transporting chemicals used in the semiconductor processing operation, but is relatively soft and therefore requires use of a secondary containment system to protect against any potential leakage or rupture.  
           [0005]    Valves used in the semiconductor industry to transport such chemicals are also contained, to protect against potential leakage, by use of a valve box. Valve boxes are designed to enclose the valve, manifold and associated connecting tubing or hosing, and are intended to withstand both vapor exposure (that can permeate through fluoropolymeric tubing) and short term liquid exposure in the event of a valve, fitting, or tubing leak. Valve boxes known in the art are constructed with flat, opaque polypropylene that is first cut to size, and then air welded together in the form of a box. Polypropylene is selected because it is extremely economical, easy to weld, and durable. Clear PVC is typically used as a window, across the front opening of the box, to allow one to view the fluid handling system contained within. The window is also removable to allow access to the system to make desired valve adjustments and/or inspections.  
           [0006]    Such known valve boxes include an O-ring seal that is compressed between the window and the valve box housing, and that operates to prevent leakage of gas or liquid from the valve box. The seal is held in place, between the window and housing, by a plurality of machine screws that extend through opposed flange portions of the window and box. The flange portions are oriented parallel with each other, and with the remaining surfaces of the box and window, and extend along the edge portion of the box and window. The seal is interposed between the two flange portions, and is compressed by the tightened machine screws. This type of seal arrangement is referred to as a “face seal” because the seal is simply positioned between the opposed flat face of the window and box flanges. With such a face seal arrangement the seal is compressed in a direction that is parallel to the axis of the screws.  
           [0007]    Such known valve boxes also include one or more polypropylene fittings welded to one or more side surfaces of the box for making connections with necessary secondary containment piping and/or for running electrical wires and other noncritical tubing through the box. PVC fittings are threaded into the polypropylene fittings in order to make the transition to the secondary containment system, which must have PVC-to-PVC connections for solvent bonding to be effective. Such a known valve box is typically hung on a wall, or attached to a rack. After the valve has been installed within the box, and all necessary fluid connections made, it is typically tested to ensure that it can serve its intended function. Valve boxes known in the art, constructed in the manner described above, must be able to endure a leak test as part of an overall secondary containment system at a pressure of 1 psig for a period of one hour.  
           [0008]    While known valve boxes, constructed in the manner described above, do provide some degree of secondary containment protection to a fluid handling system, they do suffer from some disadvantages. For example, while the use of sheet polypropylene to construct such valve boxes is cost effective from a material perspective, the task of cutting and welding together as many as  15  separate pieces is a time consuming and costly process. Additionally, such construction method produces a box that is heavy for its size, thereby limiting potential mounting and/or placement options.  
           [0009]    A major issue and concern associated with such known valve boxes is the seal design and its susceptibility to leaking when the box is pressurized. As pressure builds up within the box, due either to air during a pressure test or to fluid leaking from tubing or the enclosed fluid handling device, it acts to push the window outwardly away from the box opening. This outwardly directed pressure force causes the opposed flanges to be pushed away from one another, i.e., in a direction opposite from the compression force imposed from the machine screws, thereby causing the seal to be unloaded. Such unloading of the seal can result in gas and/or fluid leakage from the valve box.  
           [0010]    Another problem with the conventional valve box construction is the design of its box having a flat bottom that opens to the flange. This design does not provide a barrier of any sort to prevent leaking liquid from running out of the box once the window is opened or removed. Another problem with such conventional valve boxes is the use of opaque polypropylene material to build the box, which makes it difficult to observe leaks or drips within, at locations remote from the window. A still other problem associated with such known valve boxes is the need to use polypropylene fittings, as they add unnecessarily to the cost of the box and merely serve as a transition from the polypropylene box to the PVC pipe in the secondary containment system.  
           [0011]    Accordingly, it is desired that a valve box be constructed in such a manner that addresses the problems as noted above. It is desired that a valve box be constructed in a manner that: (1) is both time and cost efficient; (2) provides a seal arrangement that is not susceptible to leakage from built up pressure within the housing; (3) protects against the leakage of fluid from the housing upon opening of a valve box lid or window; (4) provides a transparent housing to enable easy visual observation of leaks and drips within the housing; (5) does away with the need to provide polypropylene fittings and (6) provides a reduction in overall weight for installation and handling purposes.  
         SUMMARY OF THE INVENTION  
         [0012]    Valve boxes, constructed according to principles of this invention, are configured having a self-energizing sealing arrangement that produces an increased sealing force with increased internal pressure, thereby improving the ability to provide a leak-tight seal in the event of liquid leakage within the box. Valve boxes of this invention generally comprise a housing including an inner chamber that extends axially through the housing from a housing base. The housing chamber includes a diameter that is defined by a housing sidewall surface that extends outwardly from the base, forming a chamber opening. The chamber opening includes a seal surface that is positioned radially inwardly towards the chamber.  
           [0013]    The valve box further includes a lid that is positioned over the housing chamber opening. The lid includes a concave center section and a seal surface disposed radially therearound. The lid seal surface is positioned radially towards the chamber, and is placed opposite the chamber opening seal surface. An annular seal is interposed between the housing chamber and lid seal surfaces. The chamber and lid seal surfaces are configured generally perpendicular to the chamber opening such that internal pressure within the chamber causes the concave center portion to impose a radially outwardly directed pressure onto the lid, thereby further compressing the annular seal to ensure a leak-tight seal.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The features and advantages of the present invention as described herein are better understood by referencing the following description and accompanying drawings:  
         [0015]    [0015]FIG. 1 is schematic perspective view of a valve box constructed according to principles of this invention;  
         [0016]    [0016]FIG. 2 is a schematic side view of the valve box of FIG. 1;  
         [0017]    [0017]FIG. 3 is a schematic bottom view of the valve box of FIGS. 1 and 2;  
         [0018]    [0018]FIG. 4 is a cross-sectional side view of the valve box of FIGS.  1  to  3 ; and  
         [0019]    [0019]FIG. 5 is a cross-sectional side view of an enlarged section of the valve box of FIGS.  1  to  4 .  
     
    
     DETAILED DESCRIPTION  
       [0020]    Valve boxes of this invention include a box and lid that are specifically designed to provide a seal mechanism capable of providing a leak-tight containment of an enclosed valve and related tubing/hosing/sensors at pressurized internal environments of at least 5 psig.  
         [0021]    FIGS.  1  to  3  illustrate a valve box  10 , constructed according to principles of this invention, generally comprising a box  12  and a lid  14 . The box  12  structure is comprised of a base  16  and four side walls  18 ,  20 ,  22  and  24  that are oriented perpendicular to the base  16 . The four side walls project outwardly from the base to define an opening of the box. The box is formed from a polymeric material, in a preferred embodiment, type II clear PVC.  
         [0022]    The box  12  can be formed by a molding process. In an example embodiment, the box is formed by a thermoforming method, and more preferably, by twin sheet vacuum forming, whereby two sheets of material are heated to a desired temperature and vacuum formed simultaneously to form the hollow part, e.g., a box structure. After molding, the panel opposite the base of the hollow part is trimmed to the desired geometry.  
         [0023]    The thermoforming method of making the box is desired because it drastically reduces the labor and time necessary to make a box, when compared to the conventional valve box construction method of welding multiple panels together. Accordingly, the molding method increases manufacturing efficiency, thus reducing manufacturing costs. Further, the twin sheet thermoforming method enables production of a thick material region surrounding the housing opening, where the two sheets are joined together, and which defines a flange  25  (FIG. 1) that is capable of supporting a desired attachment mechanism, e.g., a hinge, to permit attachment with the lid  14 .  
         [0024]    Another advantage of constructing the box by the thermoforming method is the ability to overcome flat sides and sharp corners, which are not desired in the design of structures being designed to hold pressure. Accordingly, in a preferred embodiment, the box  12  of this invention includes rounded corners and generally rounded side wall surfaces. As mentioned above, the box includes a flange or lip  25  that extends a distance perpendicularly outwardly away from the box side walls. The flange  25  provides a mating surface for a complementary portion of the valve box lid  14  to facilitate attachment therewith by means described below.  
         [0025]    The box base and side walls are configured to accommodate placement of a desired valve within the box, to accommodate attachment of the valve to the box, and to accommodate the necessary routing of tubes/hoses and/or electrical wires to the valve from outside the box. In an example embodiment, the box  12  may include one or more fittings  26  that are attached to one or more box side walls. Since the box is itself formed from PVC, unlike conventional valve boxes formed from polypropylene, there is no need to first attach a transition fitting to the box before attaching PVC fittings to the box. Rather, PVC fittings of the secondary containment system can be connected directly to the box, thereby avoiding further manufacturing time and expense.  
         [0026]    The PVC fittings  26  can be attached to the box by welding, bonding or gasketed clamping method. The welding process can be carried out by a hot air welding, wherein the fittings are welded to the inside and outside side wall surfaces of the box. In a preferred embodiment, the PVC fittings  26  are attached to the box by a friction welding process that is more time efficient welding, wherein the fitting is spun against the box to cause friction between the fitting and side wall of the box to a point where both materials soften and fuse together. Spin welding is preferred because it provides a more consistent, dependable weld, requires significantly less skill to perform, and provides a virtually guaranteed liquid-tight secondary enclosure system without having to relying on a threaded or hot air welded junction.  
         [0027]    [0027]FIGS. 2 and 3 illustrate other sides  20  and  18 , respectively, of the box to which other fittings can be attached. The exact placement of fittings, types of fittings, and number of fittings attached to the valve box housing  12  is understood to vary depending on the particular valve box application, e.g., the type of valve installed within the box. Accordingly, it is to be understood that the box fittings as illustrated in these figures is provided for purposes of reference and is not intended to limit number, type, or placement of fittings on the box.  
         [0028]    Referring now to FIGS. 2 and 3, the box  12  can also include a number of gussets  28  that extend from a bottom surface of the flange  25  to an outside surface of the box side walls  18 ,  30 ,  22  and  24 . The gussets  28  can be in the form of ribs that function to provide structural support and help stabilize to the flange  25 . In an example embodiment, the box  12  includes a plurality of gussets  28  that are spaced equidistantly therearound to provide a uniform support structure for the flange.  
         [0029]    As best illustrated in FIGS. 2 and 3, the box side wall surfaces  18 ,  20 ,  22  and  24  are configured having a stepped shape comprising a first section that extends away from the base  16  a determined distance or length, and a second section that extends away from first section and that is flared outwardly a distance from the first section. This stepped side wall construction is intentionally designed for the purpose of providing a low point in the box for the collection of any leaking liquid. Thus, any liquid that has leaked from within the valve box would run by gravity to the bottom of the box and move along the sidewall  18  from the first section to the relatively lower second section. The passage of liquid along the sidewall in this manner is aided by the rounded transition between the sidewall sections. A drain (see FIG. 3) is used to remove any collected liquid from within the valve box.  
         [0030]    As shown in FIG. 3, the sidewall  18  forming the bottom of this example embodiment valve box includes a drain  30  positioned at the low point of each sidewall. If the particular orientation of the box is not known at the time of manufacture, or it is desired to manufacture a generically oriented valve box, the drains can be placed at the low point of each side wall surface (e.g., see FIG. 2 drain  30 ).  
         [0031]    Referring to FIG. 4, the box  12  includes a collar  32  that is integral with the inside surface of the flange  25 , that projects outwardly generally parallel to an axis running through the box from the base a distance away from the flange. The collar  32  includes a distal end, forming the open end of the box and is configured in the shape of a lip  34  from a portion of the collar directed inwardly into the box. Thus, the box opening includes a lip having three surfaces  36 ,  38  and  40  that are directed generally perpendicularly outwardly from, generally parallel with, and generally perpendicularly inwardly towards, the axis running though the housing from the base  16 .  
         [0032]    The collar  32  serves at least two functions. First, it provides a structure that prevents liquid that has leaked within the valve box from running out of the valve box when the lid is removed, i.e., acts as a fluid barrier. The fluid barrier function is provided by both a ridge  42  formed from a portion of the flange projecting inwardly into the box housing, and the inwardly directed surface  40  of the collar lip  34 . Secondly, the collar provides a sealing structure for the lid, as will be better explained below, that acts to enhance the sealing effect during valve box pressurization. The box collar (described in the above structural elements of the valve box) is integral with the box and formed via the thermoforming process.  
         [0033]    As discussed briefly above, the valve box  10  includes a lid  14  that is positioned over the opening of the box  12 . Referring to FIGS. 1 and 4, the lid  14  includes a concave center section  43  that is defined along an outside perimeter by a raised lip  44 . The concave section  43  is designed to depend inwardly a distance into the box opening, and has a generally constant radius of inward curvature. Referring to FIGS. 4 and 5. The raised lip  44  (referring to the orientation of the valve box in FIG. 4) includes an inwardly directed surface  46  configured for placement against the outwardly directed box collar surface  40 , and a horizontal surface  48  configured for placement against the horizontal collar surface  38  of the box, and an inwardly directed surface  50  configured for placement against an outwardly directed surface  32  of the box collar lip.  
         [0034]    Referring to FIGS. 1 and 4, the lid  14  further includes a sidewall  52  that extends outwardly away from the lip  44  and is configured and sized to run around the box collar  32 . The lid sidewall  52  is defined at a distal end by a flange  54  that is sized and configured to fit against the box flange  25 . The lid sidewall  52  is configured having a slight outward flare, moving from the lip  44  to the flange  54 , to enable placement of the lid flange  54  over the collar lip  34  when placing the lip over and removing the lid from the box opening. The lid sidewall  52  is sized such that a compression force is imposed between the lid lip and the collar lip surfaces when the lid is positioned into a closed position against the box. Configured in this manner, the lid is designed to fit entirely over the box opening to form a compression fit against the box collar  32  and collar lip  34  surfaces.  
         [0035]    The lid is preferably formed from the same type of material used to form the box, e.g., PVC. The lid, like the housing, can be formed using the thermoforming process for purposes of improving manufacturing efficiency and reducing manufacturing costs.  
         [0036]    The lid can be attached to the box in a number of different ways, depending on the particular valve box application. For example, the lid can be attached at one of its flange ends  55  (FIG. 1) by the use of a hinge assembly (not shown), or other means that enables attached movement of the lid vis-a-vis the box. The lid can be tightened down onto the box using a variety of conventional tightening or attaching means, e.g., threaded attachment by use of machine screws that are tightened into and/or through the respective housing and lid flanges, or clamped attachment by the use of hinge clamps or the like that are clamped around the flanges.  
         [0037]    Referring to FIGS. 4 and 5, the lid includes a seal  56  that is disposed within a groove  58  provided in the lid outwardly directed surface section  46 . The seal  56  is in the form of a continuous member that is disposed completely around the surface section  46 , and is positioned along the lid surface section  46  such that it makes compression contact with an opposed surface  40  of the collar lip  34 . The seal  56  can be in the form of a solid or hollow construction, having a symmetrical (e.g., an O-ring) or asymmetrical cross section.  
         [0038]    For use in the semiconductor industry, or other applications call for the use of extremely acidic or corrosive chemicals, it is desired that the seal be formed from a chemically resistant material, e.g., Viton or the like. Alternatively, the seal can be formed from a non-chemically resistant material such as rubber, and be coated with a chemically resistant material to provide the needed degree of chemical protection. A key requirement of the seal, however, is that it provide a desired degree of squeeze when compressed, between the lid and the box, to resist given amount of pressure build up within the valve box. In an example embodiment, the seal  56  is configured having a round cross section, with a reduced radius when compared to the seal groove  58 . This is desired because it allows the seal to fit into the seal groove  58  while still protruding some distance to create the contact required on surface  46  to maintain a liquid tight seal when the lid is in a closed position over the box. Additionally, in an example embodiment, the seal has a hollow construction, that is designed to provide an added amount of elastic squeeze deformation under compression to provide an enhanced sealing effect.  
         [0039]    Referring to FIG. 4, the concave lid section  43  is designed to project inwardly inside of the housing a desired distance, parallel to the axis running through the housing from the base  16 . In an example embodiment, the concave lid section  43  projects about midway along the housing collar  32 . The concave lid section is designed in this manner, and is designed having deformable construction, for the specific purpose of providing a radially outwardly directed force to the lip  44  of the lid  14  in response to a built-up pressure force inside of the box. The pressure that becomes built up within the box imposes an outwardly directed force onto the concave lid section, that deforms the concave lid section outwardly a desired degree, and that translates to perpendicularly or radially directed force to the lid lip  44 . This perpendicularly directed force serves to further compress the seal  56  between the opposed lid lip and housing collar lip surfaces, thereby enhancing the ability of the valve box to resist leakage with increasing internal pressure.  
         [0040]    Thus, configured in this manner, the lid and housing geometry work together to form a self-energizing seal construction that provides improved resistance to increasing pressure built up within the valve box, when compared to conventional valve boxes that have sealing surfaces that move away from one another when exposed to pressurization within the box.  
         [0041]    Valve boxes, constructed according to principles of this invention, display several advantages when compared to convention valve boxes as described above. Use of the thermoforming method for forming the valve box housing and lid enables the valve box to be formed in a single 15 minute forming cycle that requires less than 15 minutes of trimming, and that enables forming a box have rounded surfaces. This compared to the labor intensive multistep process associated with cutting and welding multiple panels to produce a box having squared comers and surfaces.  
         [0042]    Additionally, use of the thermoforming process enables production of a valve box that weighs roughly 40 percent less than that of a comparably sized conventional valve box, thereby facilitating system installation. Also, the ability to use spin welded fittings facilitates valve box construction and reduces the chance of a leaks using conventional fittings. Valve boxes of this invention are also configured having a liquid collection reservoir, without a welding step, to avoid fluid leaking from the housing upon opening or removing the lid. Also, valve boxes of this invention formed from transparent or clear PVC enable viewing into the box to observe fluid leakage from above, from the side, or from below the box. Further, valve boxes of this invention comprise a fluid drain that, in conjunction with the fluid reservoir, enable collected fluid within the box to be drained or removed therefrom from a safe distance.  
         [0043]    The valve box feature of a self energizing seal is critical to being able to provide a valve box capable of meeting or exceeding a desired or necessary valve box pressure rating for use in certain applications. Conventional valve boxes are known to leak or fail during pressure testing up to 1½ psi. Valve boxes of this invention size are able to provide leak-tight service at pressures of at least 5 psi.  
         [0044]    Other modifications and variations of valve boxes, constructed according to principles of this invention will be apparent to those skilled in the art. It is, therefore, to be understood that within the scope of the appended claims, this invention may be practiced otherwise than as specifically described.