Abstract:
A substantially gas tight cover for an open-top structure such as a tank requires very few fasteners and allows for thermal expansion and contraction movement while still maintaining the nearly complete gas seal. Unique metal extrusions are assembled on-site in a modular system that is easily put together. An important component of the system is a gutter extrusion which includes an elongated gutter and flanges with sealing gaskets for engaging the top surface of the concrete tank rim as well as engaging the inner wall of the tank below the top. At intervals along the gutter strip are hold-down clips that interlock with the gutter extrusion and are secured in the concrete of the tank, spaced back from the tank edge. Fasteners in the inside face of the tank preferably are avoided. Main spanning beams for the tank cover are connected to the gutter extrusions in a way so as to allow for thermal expansion and contraction, without losing the gas seal.

Description:
This application is a continuation in part of Ser. No. 09/248,775 filed on Feb. 12, 1999 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention is concerned with covers for large tanks, particularly tanks in sewage treatment processes, for containing malodorous gases. 
     Tank covers of the general type with which this invention is concerned are shown in U.S. Pat. Nos. 6,151,835, 6,012,259, 5,941,027, 5,911,662, 5,617,677, 5,545,358 and 5,325,646. These patents are incorporated herein by reference. 
     Increasingly there is a need for covers to enclose in-ground and above ground tanks used for storing waste materials including sewage, chemical sludge, petroleum products and other volatile and odorous materials. The materials generally are stored for later disposal or treatment in such tanks. Such a cover must be substantially gas tight for controlling odors in the vicinity of the tank site and for trapping potentially hazardous gases. Often the gases are withdrawn for cleaning, such as by biofiltration, placing a slight vacuum in the airspace above the tank. The tank should be substantially seated to minimize intrusion of air. 
     A tank cover is generally too large to be conveniently or cost effectively shipped in an assembled form from a manufacturer to the site of the tank. Because of this, tank covers for relatively large tanks are generally shipped as components and assembled at the site. 
     Prior art tank covers made of steel are heavy and expensive even to ship in component form. Further, such covers usually require welded connections and bolted connections in their assembly. As such, skilled personnel may be necessary to carry out the assembly, and the assembly process may be lengthy and costly. Some prior tank covers have been formed of sheet metal panels assembled at the site. 
     It is a purpose of the present invention to produce a highly modular tank cover system which requires very few fasteners and which allows for thermal expansion and contraction movement while still maintaining an almost complete gas seal. 
     SUMMARY OF THE INVENTION 
     The invention accomplishes these goals with unique metal extrusions which are assembled on-site in a modular system that is easily put together, with almost no fasteners and with other features providing for efficiency in installation and an effective substantially gas tight seal. 
     The system includes spanning beams of the appropriate size and spacing for the tank span to be covered. This may be, for example, approximately 12 feet to over 20 feet. Such span lengths can overlap with those addressed by the tank cover structure in U.S. Pat. No. 6,012,259, and can extend to greater lengths with larger beams or closer beam spacing. 
     In the system of the invention, a modular and nearly fastener-free cover system, substantially gas tight, is provided for open-top tanks which may be of the types described above. An important component is a gutter extrusion which includes a elongated gutter and flanges with sealing gaskets for engaging the top surface of the concrete on the tank as well as the inner wall of the tank several inches below the top. The gutter extrusion has gas seals at each of these two contact areas. The gasket seal which bears against the inner wall of the tank preferably comprises a structural member as well as a seal, helping hold the flange of the gutter extrusion from the tank wall. The seal preferably is pleated, with a type of bellows configuration, allowing the seal to compress to varying degrees on an irregular concrete surface, while still maintaining a seal. This and other seals may advantageously be formed of multi-durometer Santoprene. 
     The gutter strip is secured to the tank structure by a series of hold-down clips which are spaced apart at intervals, primarily at positions adjacent to the series of beams. These hold-down clips advantageously are extrusions, cut to the desired width (e.g. about 4 inches), with interlocking structure for sliding interlocking engagement with the gutter extrusion upon assembly. The cross section of the hold-down clip is configured to mate with the cross section of the horizontal flange on the gutter strip. On assembly to the tank, these hold-down clips are secured into the concrete using concrete anchor bolts, at a position somewhat removed from the tank edge, e.g. about 5 inches away. This provides for a stronger concrete anchoring by removing the anchor from near the edge of the concrete, and also helps avoid problems with other structure existing around the tank, such as handrails. Further, the bolt hole in the hold-down clip for receiving the anchor bolt preferably is angled such that the bolt is assembled obliquely from the outside, at an angle which may be about 15° to 30°. This further aids in assembly by avoiding problems with handrails and other structure, and also helps draw the clip into firm engagement with the gutter strip. The purpose of the clips is to structurally prevent the gutter strips from pulling or tipping inwardly into the tank. 
     It is an important feature that the gutter is secured only with fasteners entering into the horizontal surface of the concrete, without requiring any fasteners to be secured into the vertical face of the tank, providing for considerably easier installation and avoiding the requirement that the installer enter the tank. 
     The gutter extrusion is thus cantilevered over the tank. Structural spanning beams rest on a platform at the inward side of the gutter extrusion, the entire extrusion having a relatively large width, e.g. 7 inches to 12 inches, and preferably about 10 inches to 11 inches, and extending over the tank about 8 inches to 9 inches in one preferred embodiment. These dimensions of course depend on the scale of the tank cover project, but the preferred dimensions will serve spans of a length somewhat more than 20 feet. 
     The manner which the spanning beams are supported on and secured to the gutter extrusion forms an important feature of the system. Thermal expansion and contraction are encountered to a considerable degree in large tank covers, primarily cause by changes in external atmospheric conditions. A beam of 20 feet or more can exhibit a length difference of ¼ inch to ½ inch, between extremes of temperature. Importantly, the beams in the system of the invention are not secured to the gutter extrusions by fasteners, but instead are retained by a unique connection which allows for thermal expansion/contraction (length of the beam) and for movement in the perpendicular direction as well. This connection comprises a hold-down member which assembles slidingly into the gutter extrusion, at the side of the extrusion inboard of the tank. The gutter extrusion is formed in a preferred embodiment with a “key” shape which receives the slidable hold-down member by end assembly, such that the hold-down member cannot pull upwardly out of the gutter extrusion. Various such slidable, interlocking shapes can be used. The slidable hold-down connection member allows the beams to be moved to the appropriate positions on assembly, and also allows for other shifting in position which may occur due to thermal expansion and contraction affects. 
     The decking of the tank cover system preferably is formed of assembled extrusions (e.g. aluminum extrusions), similar to what is shown in U.S. Pat. Nos. 6,151,835, 6,012,259, 5,941,027, 5,911,662 and 5,617,677, referenced above. These preferably aluminum extrusions are assembled in substantially sealed relationship in panels, each panel resting on two of the spaced apart beams. The panels may be formed of interlocked deck slats extending in a direction perpendicular to the beams, with panel end members attached to edge deck planks and having flanges extending outwardly for sealing, and channel sections extending perpendicular to the deck planks and parallel to the main beams, receiving the ends of the deck planks, and with flanges which extend outwardly to rest on the beams. Gasket seals are positioned between the top of the beam and the flange of the panel. In a preferred embodiment, these gasket seals are slidingly connected to the tops of the extruded beams, in an interlocking connection, and with each gasket seal having two main ribs extending in parallel, each rib positioned to engage the underside of a flange from the deck panel. 
     For sealing the space at ends of the main beams, extruded flashing is secured to the gutter extrusion. These flashing components are continuous along sides of the tank, running perpendicular to the lengths of the beams. The flashing components may be Z-shaped, with a bottom flange having an interlock gasket seal for engaging downwardly against an outer end of the beam platform of the gutter extrusion. This component is secured down to the gutter extrusion, and tapered, self-tapping screws are advantageously used. 
     The upper flange of the flashing member retains a further gasket on its upper surface, and this is for sealing engagement with the overhanging flanges of the deck panels that extend in this direction. The edge of the sealing gasket abuts against the ends of the gasket seals which are secured to the tops of the beams, providing a part of the system gas seal, which is substantially air tight. 
     Another component of the assembly is a cap which is used on top of each beam, running parallel to the beam lengths. The cap, which may be about one-quarter inch thick and about one inch or so wide and formed of stainless steel, has left and right edges which clamp down against the edges of the two adjacent panels on either side of the beam, compressing the overhanging flanges of those panels down against the beam top gasket. The caps may be secured to the beam by self-tapping screws. 
     Accordingly, the tank cover system of the invention provides versatility in serving a wide variety of tank sizes, provides for easy and efficient assembly, substantially avoids fasteners and particularly avoids rigid connections between the beams and the peripheral beam support, makes wide allowance for thermal expansion and contraction, and provides a high integrity gas seal. These and other objects, advantages and features of the invention will be apparent from the following description of preferred embodiments, considered along with the drawings. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional elevation view showing a spanning beam and adjacent cover panels forming a part of the system of the invention. 
     FIG. 2 is a sectional elevation view from a position perpendicular to that of FIG. 1, showing a spanning beam of the system resting on a gutter extrusion, which is secured to the edge of a tank. 
     FIG. 3 is a perspective view showing a hold-down slidable connection member. 
     FIG. 4 is a perspective view showing a portion of the assembly shown in FIG.  2 . 
     FIG. 5 is a perspective view showing a clip which retains the gutter extrusion in place. 
     FIG. 6 is a perspective view showing a section of an elongated flashing member which seals the assembly across ends of the beam. 
     FIG. 7 is a sectional elevation view showing an elastomeric gasket seal used on tops of the beams. 
     FIG. 8 is a perspective view showing a section of an elastomeric gasket seal secured to the gutter extrusion and which bears against the tank wall. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 shows a portion of the system in cross section. One of the main spanning beams  10  is shown supporting a pair of adjacent deck panels  12  and  13 . As noted above, these panels can be formed generally in accordance with the panel constructions shown in the previous patents referenced. The major components may be aluminum extrusions, some of the extrusions being deck planks as indicated at  16  and channel sections as shown at  18 , the channel sections being assembled onto the ends of the series of deck planks  16 , retaining the panels together. These channel sections pursuant to the invention also include overhanging flanges at  20  to extend over the top flange  22  of the beam  10 , each flange  20  preferably having a downwardly depending lip  24 . These lips extend over an elastomeric gasket seal  26 , shown assembled on to the top of the beam flange  22  and captured therein by interlocking cross section, which may be generally a “T”-shape. The gasket  26  is shown in detail in FIG. 7, with the “T”-shaped interlock  28  at the bottom of the gasket, this being shaped complementarily to an extruded cavity in the beam flange. The gasket  26  preferably has hollow edge ridges or flanges  30  for compressibly engaging the channel flanges  20  when assembled thereon, and it also includes a pair of protruding ridges  32  at the bottom side of a main section  34  of the gasket. In the uncompressed state, the gasket  26  preferably is curled upwardly somewhat, so that the main section  34  is concavely curved and the flange ends  30  are at the upper edges of the curved configuration. When the gasket is engaged by the weight of the panels, it compresses down generally to the configuration shown in FIG. 7, and the bottom ridges  32  are pressed tightly and compressibly against the top of the beam, aiding in the gas seal. 
     FIG. 1 also show that an extruded, continuous cap  36  preferably is included in the assembly, pressing down against the channel flanges  20  to increase the sealing compression against the gasket  26 . The cap  36 , which may be of stainless steel, covers the gasket  26  at tops of the beams and aids in sealing. It may be retained down to the beam  10  by self tapping screws such as shown at  38 , bored down through the center of the gasket  26  and tighten into the beam. 
     FIG. 2 shows a portion of the tank cover assembly from a position at 90° to the view shown in FIG.  1 . Here, the edge  40  of the concrete tank on which the assembly is positioned. The beams  10  rest on a gutter extrusion  42 , continuous throughout the length of a side of the tank which is represented at  40 . A portion of this assembly is also shown in FIG. 4, and this discussion will refer to all of the drawings. 
     The gutter extrusion  42  includes a gutter  44 , a platform indicated at  46  and extending over the tank, and horizontal and vertical flanges shown at  48  and  50 , for bearing against the top surface  40   a  and the inside vertical wall  40   b  of the tank as shown. These bearing flanges each have a gasket seal, assembled in the sliding, interlocking cross section arrangement which is typical of these components and shown in FIGS. 1 and 7 as well as FIG.  2  and FIG.  4 . The horizontal seal  52  is compressible and preferably includes a series of deflectable fins extending lengthwise and similar to fins  54  shown on a similar gasket seal  56  in FIG. 5, attached to a gutter retention clip  58 . The clip pad or gasket  56  is also shown in FIG. 2, but it has no sealing function, the retention clips or brackets  58  being non-continuous and of the proportions, for example generally shown in FIG.  5 . These clips are located at intervals as needed, primarily at locations of the beam ends  10 . 
     The retention clips  58  engage the gutter extrusion  42  preferably in a sliding interlocking cross section arrangement such as shown at  60 , similar to other component-to-component assemblies of this system. Anchor bolts  62  retain the clips  58  to the concrete tank rim, preferably at an angle as discussed above and as shown in FIG.  2 . The anchor bolt  62  passes through a bore  62   a  in an angle facet  64  of the clip, as seen in FIG.  2  and as better illustrated in FIG.  5 . 
     As noted above, the gutter extrusion  42  engages, in substantially sealing engagement, both the horizontal surface  40   a  and vertical wall  42  of the concrete tank rim  40 . The gasket  66  engaging the wall  40   b  is indicated in FIG. 2 but better seen in FIG.  8 . The seal  66  is a structural component as well as sealing component, and may be formed in pleated or bellows type configuration as shown in FIG.  8 . The seals, particularly the seal  66 , may be of multi-durometer elastomeric material, advantageously Santoprene. Again, the gasket  66  is provided with an interlocking cross section as shown at  68  for engaging in an interlocking fashion with the aluminum extrusion. This seal, like the seals discussed above, may be provided with fins or wipers  70  to aid in the sealing function. The elastomeric gasket seal  66  shown in FIG. 8 is capable of sealing against a wall with considerable irregularities. As shown in FIG. 2, the gasket seal  66  also serves to hold the extrusion  42  off the concrete wall, compressing the seal  66  and in that sense comprising a structural component. 
     As mentioned above, the end of the beam  10  rests on a platform  46  formed as part of the aluminum extrusion  42  and overhanging the tank. The beam is not fixedly secured to the gutter extrusion  42  in a preferred embodiment. Instead, as explained above, it is allowed to move in the lengthwise direction of the beam to accommodate thermal expansion/contraction, thus sliding left to right on the platform as seen on FIG.  2 . The beam is retained on the platform by a hold-down slidable member  72 , also seen in FIG.  3 . This member  72  can be an aluminum extrusion, extruded in the direction of the arrow  74  in FIG. 3, then cut into the shape shown. This shape engages with an undercut slot extending between the acute undercuts  76  and  78  in FIG. 2, providing a connection that lets the hold-down component  72  slide along the length of the gutter extrusion  42  (into and out of the paper in FIG.  2 ). 
     As can be seen in FIGS. 2 and 3, the hold-down member  72  has flanges or lips  80  which capture the beam flange edges  82 , one of which is seen in FIGS. 2,  4  and  1 . This connection is also slidable, allowing the noted expansion/contraction movement of the beam relative to the hold-down  72  and the gutter extrusion  42 . Thus, the beam end is allowed to move in both perpendicular directions, aiding in correct positioning of the beams upon assembly and accommodating thermal expansion/contraction. 
     As explained above, the panels such as those  12  and  13 , shown in FIG. 1, and made up of assembled aluminum extrusions, rests on the tops of the beams  10 . This provides the needed seal at left and right of each beam, where the beam meets the decking panels. At ends of the beams, a seal is needed for the space between beams, and this is provided by a flashing member  86  which is continuous throughout the length of a side of the tank. This flashing member  86  is shown in FIGS. 2,  4  and  6 . It can be of a generally Z-shaped configuration in cross section, having a tall web  88 , inwardly turned upper flange  90  and an outwardly turned lower flange  92 . At the bottom, the lower flange retains an interlock configuration and elastomeric sealing gasket  94 , bearing down against the gutter extrusion platform  46 . Fasteners, such as self tapping screws  96 , preferably are used to retain the flashing member  86  to the gutter extrusion. At the upper end of the flashing  86 , however, the flashing preferably is not fixedly secured to the beam  10 . The upper flange  90  supports, an interlocking cross section arrangement as previously illustrated, a gasket  98 . The upper flange  90  engages downwardly against the sealing gasket  26  which is secured to the top of the beam  10 . When the panels are erected onto the beams, the channel members  18  (FIG. 1; also seen in FIG. 2) terminate prior to the end of the beam  10 , preferably at the point where an overhanging flange  100  on an extrusion  102  extends outwardly (to the right in FIG. 2) from the extrusion  102 . The extrusion  102  can be a variation of the deck planks  16 , used as a boarder member for the panel and including the special flange  100  for sealing this part of the system. As shown, this sealing flange  102  bears down against the gasket  98  at the top of the flashing  86 . Since the elastomeric beam top gasket  26  preferably abuts into the edge of the flashing top flange  90  and/or its gasket  98 , and the corner of the decking panel closely engages both gaskets, the seal is substantially gas tight in this region. 
     At ends of the gutter extrusions  42 , i.e. at ends of the tank, the gas seal is made in a different way. For example, horizontal flashing may extend from the lower flange of the beam  10  closes to that end of the tank, across to an engagement with the wall of the tank. Such horizontal flashing (not shown) may then engage in seal relationship with the inward surface of the platform  46  of the gutter extrusion  42 , which can be envisioned from FIG.  4 . If FIG. 4 were assumed to show the left end of the gutter extrusion  42 , this extrusion end can be sealed against the tank endwall, and if horizontal flashing can then be placed in engagement with both the lower beam flange  82  and the platform  46 , also sealing against the tank endwall. Other arrangements are possible as well. 
     The above described preferred embodiments are intended to illustrate the principles of the invention, but not to limit its scope. Other embodiments and variations to this preferred embodiment will be apparent to those skilled in the art and may be made without departing from the spirit and scope of the invention as defined in the following claims.