Abstract:
Assemblies and methods are provided to divert liquids that would otherwise infiltrate utility manholes or other hatchways, while allowing gases to vent to the atmosphere. Preferred embodiments of the assemblies comprise a cover support frame, a sheet of water-repellent gas-permeable material occluding the central opening of the support frame and a cover mated to the frame. Preferably, a stiffening ring or other means of providing structural rigidity to the venting structure is provided. The assemblies are lightweight and are simple to install, and can be fabricated from materials that are readily available. Moreover, the assemblies can be easily modified to accommodate field conditions.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional of application Ser. No. 09/616,019, filed on Jul. 13, 2000 U.S. Pat. No. 6,464,425, which claims the benefit of U.S. Provisional Application No. 60/144,381, filed on Jul. 16, 1999, the disclosure of which is incorporated by reference herein. 
    
    
     FIELD OF INVENTION 
     The present invention relates to apparatuses and methods to minimize the infiltration of liquids through hatchways, particularly utility manholes that provide entrance to subterranean chambers. 
     BACKGROUND OF INVENTION 
     According to information available in the environmental protection industry, the source of at least 35 percent of the inflow to sewage or wastewater treatment plants is rainwater or other non-wastewater liquid that has infiltrated the collection system. Reducing the amount of infiltrating water will reduce the volume demands imposed on these wastewater treatment plants and, thereby, decrease operating costs. Some wastewater authorities do not provide their own treatment, but pipe their wastewater to other facilities for processing, These authorities are charged monthly by the gallon of liquid piped and would immediately benefit by reducing the amount of rainwater or other non-wastewater infiltration. Private wastewater plants can realize the same benefits. 
     Other industries maintain extensive networks of equipment and wiring beneath the ground, for utilities such as electric, gas, fiber optic, telephone and cable services. These companies also desire to reduce the amount of rainwater infiltration to their utility vaults and thus of time and costs required to maintain manholes and vaults in dry and well-ventilated condition. 
     Most of the infiltrating liquid enters the above-mentioned systems through pick holes in manhole covers, which are perforations made through the cover to facilitate its removal and replacement using a pick or other tool. Some water also may enter between the cover and frame, especially if the assembly has become loose or worn. 
     Known systems for minimizing unwanted liquid infiltration include a variety of mechanical sealing devices, intended to prevent liquids from entering by these routes while allowing any gases that may be present to vent to the atmosphere. It has proved difficult to achieve both of these goals in a manner that would be cost-effective, where a large number of entry points are involved. 
     A common approach is to insert a polypropylene or metal bucket between the cover and the interior of the frame to capture and retain the infiltrated liquids. When filled to capacity, these buckets are difficult to remove because they are below the street level and may weigh over 20 pounds. Some devices also provide pressure-relief valves to vent the gases that would otherwise accumulate within the manhole, but the presence of these valves makes it still more difficult to open and close the manholes. U.S. Pat. No. 4,067,659 to Campagna, Jr. et al. discloses a bucket-like structure comprising a circular supporting flange that rests on the internal flange of a manhole cover support frame. A valve-member incorporated into the bucket relieves excessive gas pressure in the space beneath the bucket. Similar devices are disclosed in U.S. Pat. No. 4,650,365 to Runnels, U.S. Pat. No. 4,919,564 to Neathery et al., U.S. Pat. No. 4,957,389 to Neathery, U.S. Pat. No. 5,591,200 to Barton, and U.S. Pat. No. 5,957,618 to Sims et al. The later inventions are focused toward protecting the valves from damage and making the buckets easier to install and remove from the manhole. A similar approach is disclosed in U.S. Pat. No. 4,305,679 to Modi, which discloses the use of a plurality of expanding braces to compress an impermeable flexible membrane against the interior of the manhole frame. The resulting structure captures water flowing through the manhole cover and blocks water from entering the manhole through the joints between the frame and the manhole chimney. The braces must be compressed and removed from the frame to gain entry to the manhole. 
     Another approach is to install a closure plate to block the inflow of water. The use of a plate in place of a bucket reduces the amount of water collected beneath the cover. These devices typically include pressure relief valves to vent gases accumulating beneath the cover plate. The cover plates are designed to rest on an integral flange within the manhole frame. If no flange is present, a retaining ring or other suitable support structure must be installed. Devices of this type are disclosed in U.S. Pat. Nos. 3,712,009 and 3,798,848 to Campagna, U.S. Pat. No. 3,969,847 to Campagna et al., U.S. Pat. No. 3,973,856 to Gaglioti, and U.S. Pat. Nos. 4,030,851 and 4,512,492 to Graybeal. 
     Another approach is to provide an elastomeric seal between the contact surfaces of the cover and frame. The holes in the cover are filled to minimize infiltration or a cover without holes is used. The seal may be held in place by the weight of the cover or bolted securely to the frame. The main drawback of sealing the manhole in this manner is that the gases within the manhole chimney do not vent to the atmosphere and, therefore, may accumulate to hazardous levels. It is also more difficult to open and reseal the access opening. U.S. Pat. No. 4,763,449 to Vigneron et al. provides an elastomeric sealing ring interposed between the cover and an integral flange within the frame. A plurality of bolts and movable flanges recessed within the frame are used to hold the cover firmly against the sealing ring. These bolts and flanges must be loosened or removed to gain entry to the manhole. U.S. Pat. No. 4,934,715 to Johnson discloses the use of an elastomeric gasket to form a water-tight seal between a cover and frame. The circular groove must be formed within the frame to receive the gasket. The gasket is squeezed between the frame and cover using a plurality of bolts. U.S. Pat. No. 4,101,236 to Meyer provides a manhole cover with an O-ring groove and no perforations. The O-ring groove is positioned to allow an elastomeric O-ring to form a seal between the cover and the contact surface of a conventional manhole frame. U.S. Pat. No. 4,440,407 to Gagas discloses the use of an L-shaped elastomeric gasket to provide a seal between the contact surfaces of a manhole cover and frame. U.S. Pat. No. 4,597,692 to Gruenwald discloses the use of elastomeric gaskets and plugs to minimize inflow of water by forming a seal along the perimeter of the manhole cover and closing the perforations within the cover. 
     SUMMARY OF INVENTION 
     The present invention disclosed herein addresses the drawbacks of known devices and methods. One aspect of the present invention provides venting structures that utilize liquid-repellent, gas-permeable membranes to capture liquids that infiltrate manhole covers, while allowing gases to pass through the membranes. Certain preferred assemblies will also be useful to prevent particulate solids, such as sand or dirt, from penetrating between the cover and frame and causing them to bind together. The preferred assemblies are light-weight and simple to install and can be fabricated from materials that are widely available. The most preferred assemblies can be modified to accommodate field conditions. 
     In accordance with one embodiment of the present invention, there is provided an assembly that minimizes the infiltration of liquids into a manhole or other hatchway. The assembly comprises a venting structure that is installed between the manhole cover and frame. The venting structure, most preferably, utilizes a water-repellent gas-permeable fabric to contain or divert liquids that would otherwise enter the manhole through openings in the cover or between the cover and frame. The fabric allows gases and vapors that may exist in the manhole chimney to vent to the atmosphere. 
     In a preferred embodiment of the present invention, the assembly comprises a cover support frame; a sheet of water-repellent gas-permeable material covering the central opening of the support frame and preferably folded over a stiffening ring; and a cover mated to the frame. More preferably, additional sealing materials and/or packing elements are used to minimize movement of the cover in the frame and provide a non-wearing surface for the sheet of material, and to improve the liquid-tight seal between the cover and flange. 
     In another embodiment, the invention provides a venting structure for minimizing the infiltration of liquid into an access opening, such as a manhole or hatchway, while allowing gases to escape through the access opening. The venting structure comprises a sheet of liquid-repellent, gas-permeable membrane adapted to substantially occlude an opening in the venting structure. Preferably, the venting structure is adapted to be installed between the cover and the support frame that defines the access opening. The sheet may be adapted by cutting and folding portions of the sheet over a stiffening ring to provide structural support. The sheet may also be adapted by fluting its edges to form a dish-like structure conforming to the perimeter and underside of a provided cover. 
     In accordance with another aspect of the present invention, there is provided a method for minimizing infiltration of liquids into an access opening while allowing gases to escape through the access opening. Preferably, the method includes cleaning the surfaces of the frame and cover to remove dirt and other abrasive material; placing a venting structure over the access opening, partially overlapping the frame; and lowering the cover into place so that the venting structure is held in place between the cover and frame. More preferably, the method includes inspection of the assembly to determine that the cover is securely seated against the frame so that it does not move under normal traffic conditions and, if the frame is installed in the ground, that the cover is level with the top of the frame and grade. Most preferably, if the assembly is unsatisfactory, the method includes disassembling the assembly and providing a sealing element or packing material is placed along the rim of the frame to improve the fit between the cover and frame. Most preferably, the assembly process and inspection are repeated until the cover is securely seated against the frame. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top plan view of a manhole frame and cover utilized with a preferred embodiment of the present invention; 
     FIG. 2 is a side elevation view of the manhole frame and cover of FIG. 1; 
     FIG. 3 is a bottom plan view of the venting structure of a preferred embodiment of the present invention; 
     FIG. 4 is a bottom plan view of an unfolded sheet of liquid-repellent, gas-permeable material, showing cut marks and fold lines to form the venting structure of FIG. 3; 
     FIG. 5 is a top plan view of a sheet of liquid-repellent, gas-permeable material adapted for use as a venting structure in a preferred embodiment of the invention; 
     FIG. 6 is an exploded view showing the venting structure of FIG. 3 in relation to a manhole cover and frame; 
     FIG. 7 is a fragmentary cross-sectional view on an enlarged scale depicting the cover and frame of FIG. 2 in conjunction with the venting structure of FIG. 5; 
     FIG. 8 is an exploded view showing the venting structure of FIG. 3 in relation to a manhole cover and frame; 
     FIGS. 9 and 10 are fragmentary cross-sectional views on an enlarged scale of the assembly of FIG. 1, depicting a cover and frame in conjunction with the venting structures in accordance with certain embodiments of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of this invention are most suitable for use with conventional utility manholes as illustrated in FIG.  1  and FIG. 2. A typical manhole installation comprises a frame  5  over a manhole chimney  9 , and a manhole cover  3 . Frame  5  defines access opening  1  within frame  5 . Frame  5  is typically installed in ground so that the top of frame  5  is conforms to the level of the surrounding grade  7 . Cover  3  is mated to frame  5  so that cover  3  fits within frame  5  resting on the upwardly-facing surface of flange  8  and the top of cover  3  is level with surrounding grade  7 . 
     A venting structure  10  in accordance with a preferred embodiment of this invention is illustrated in FIG.  3 . Venting structure  10  comprises a sheet  19  of water-repellent, gas-permeable material that has been adapted to occlude access opening  1  while overlapping flange  8 . Where sheet  19  has only one water-repellent side, the side opposite the water-repellent side is designated, preferably, as the underside  18 . Stiffening ring  15  comprises a central opening  16  and an outer edge  17  that is adapted to fit within frame  5 , and preferably resting on flange  8 . Stiffening ring  15  acts as a frame, providing structural support to venting structure  10 . Preferably, stiffening ring  15  is adapted to fit snugly within frame  5  while resting on the upper surface of flange  8 . More preferably, stiffening ring  15  is made of a compressible material so that it serves as a seal element when squeezed between cover  3  and flange  8 . Edge portions  11  are folded over stiffening ring  15  and attached to underside  18  in the central portion of sheet  19  accessible through opening  16 . 
     Assembly  20  comprises the components of venting structure  10 . Sheet  29  of liquid-repellent, gas-permeable material is cut to the shape necessary to make the sheet  19  used in venting structure  10 . The position of stiffening ring  15  is shown in outline. Edge portions  11  are formed by cutting away excess material  22  along cut lines  24  so that edge portions  11  do not overlap each other when folded to form venting structure  10 . Folds are made along fold lines  23  near the outer edge  17  of stiffening ring  25 . 
     As discussed further below, stiffening ring  15  merely needs to fit on flange  8  of frame  5 . Edge portions  11  should be large enough to fold over stiffening ring  15  and tack to the underside  18  of sheet  19 . Methods to determine the dimensions of assembly  20  with edge portions  11 , excess material  22 , and fold lines  23  will be apparent from the foregoing. Also, assembly  20  may be prepared with other shapes than illustrated. An eight-sided shape is shown for assembly  20  for simplicity of illustration. Circular shapes may be approximated more closely by increasing the number of edge portions  11 . It will also be apparent that a functionally acceptable venting structure can be made by folding edge portions  11  onto the underside  18  of sheet  19  without cutting away excess material  22 . If field conditions do not necessitate structural stiffness in venting structure  10 , stiffening ring  15  may be omitted. 
     Edge portions  11  can be secured to underside  18  using starch, adhesives, or other tacky substances. For certain applications, securement of edge portions  11  can be temporary in nature, as it will be sufficient that they are held in position until cover  3  is seated on frame  5 . Edge portions  11  then will be held in place by the weight of cover  3 . 
     Preferably, the sheet of liquid-repellent, gas-permeable material used for venting structure  10  comprises composites or laminates of woven fabric and gas-permeable plastic membranes. More preferably, the gas-permeable plastic membranes will be made of a spun-bonded high-density polyethylene, spun-bonded polypropylene, spun-bonded polyester, spun-bonded polyacrylic, spun-bonded polyaramid, or an expanded polytetrafluoroethylene, and laminates and composites with one or more of the more preferable membranes or with a woven fabric. Other more preferable materials include woven fabrics, such as nylon, polyester, polyacrylic, polyaramid or blends thereof, which have been chemically treated to repel water. These materials can be adapted for use in this invention by mechanical means, such as folding or pleating, by heat-treatment, or by other means known to the art. Commercially available sheets comprise a range of thicknesses, tensile strengths, and other mechanical properties relevant to their use in venting structures of the types disclosed herein. Such sheets may be selected to provide the properties most preferred for particular applications and field conditions. 
     Installation of venting structure  10  is illustrated in FIG.  6 . Venting structure  10  is placed onto frame  105  so that stiffening ring  15  rests on flange  108  and venting structure  10  occludes access opening  101  as defined by frame  105 . Venting structure  10  is installed, preferably, with a water-repellent side upward, that is, with underside  18  facing the manhole chimney  109 , to take the fullest advantage of the water-repellent, gas-permeable properties of the material. Cover  103  is placed onto frame  105  so that stiffening ring  15  is squeezed between cover  103  and the upper surface of flange  108 . Sealing element  111  may be interposed between venting structure  10  and flange  108 . 
     The use of sealing element  111  is particularly preferred in embodiments of the venting structures that do not include stiffening rings. Sealing elements should be selected to improve the water-tight seal between the venting structure and flange and to reduce abrasion of the water-repellent, gas-permeable material where it contacts the flange. Preferably, a gasket with an “L”-shaped cross-section is used to obtain the desired water-tight seal. A sealing substance, such as a caulk of silicone or polyurethane composition, may be preferred depending on field conditions, especially if the cover or frame are old or worn. Alternative materials, such as oakum or packing materials known to the art, may be used to obtain the desired seal. 
     The assembly  30  for another preferred venting structure  40  is illustrated in FIG. 5. A sheet  39  of liquid-repellent, gas-permeable material is cut to a shape that will occlude access opening  1  and overlap flange  8  and the perimeter of cover  3 . The position of stiffening ring  45  is shown in outline. Edge  34  of sheet  39  is fluted by pleating, heat treatment, or some other method known to the art. 
     Installation of venting structure  40  is illustrated in FIG.  7 . Venting structure  40  is placed onto frame  205  so that stiffening ring  45  rests on flange  208  and venting structure  40  occludes access opening  201  as defined by frame  205 . Similarly to venting structure  10 , venting structure  40  is installed, preferably, with a water-repellent side upward, that is, with underside  47  facing the manhole chimney  209 . Cover  203  is placed onto frame  205  so that stiffening ring  45  is squeezed between cover  203  and the upper surface of flange  208 . The fluted edge  34  of assembly  30  folds upwardly to form sidewall  44  which substantially surrounds the vertically-oriented rim of cover  203 . If sidewall  44  extends vertically-oriented rim of cover  203 , excess sidewall material maybe folded onto surface grade  207  and secured to surface grade  207  by use of tar or other sealing material, providing additional protection against infiltration of liquids between frame  205  and venting structure  40 . Cover  203  rests directly on stiffening ring  45 . Sealing element  211  may be interposed between venting structure  40  and flange  208 . 
     Certain liquid-repellent, gas-permeable materials can be shaped to form rigid structures through application of heat and mechanical deformation. Sidewall  44  can be created as a rigid structure by bending and pleating the fluted edge portion  34  of sheet  39  at the same time as the material is softened by application of heat. Folding or rolling the outer edge of sheet  39  at the same time that heat is applied will shape the outer edge of the sheet to form a rigid rim. 
     The venting structures  10  and  40  illustrate two of the preferred embodiments of the venting structure of this invention. These structures, and those of similar construction, may also be used to prevent infiltration of liquids into valve boxes and above ground hatchways. Other embodiments will become obvious to those persons having ordinary skill in the art. For example, the venting structure of this invention may take the form of a bucket or plate having an opening occluded by a layer of water-repellent, gas-permeable material. Another variation entails installing the venting structure within the manhole chimney below the frame, rather than installing it within the frame as illustrated for venting structures  10  and  40 . 
     In another aspect, the invention comprises a method for minimizing infiltration of liquids into the access opening of a manhole while allowing gases within the manhole chimney to escape to the atmosphere. In this method, manhole cover  503  is removed, and the top surface of flange  508  and bottom surface  502  of cover  503  are cleaned to remove dirt, corroded metal fragments, and other substances that would increase the wear on the fabric or interfere with formation of a close contact between the material and the frame. The venting structure  10  is then placed over frame  505  with stiffening ring is resting on flange  508 . Manhole cover  503  is lowered onto frame  505  in such a manner that venting structure  10  is neither dislodged or damaged. Cover  503  is then inspected to determine that cover  503  fits securely within frame  505  so that cover  503  will not move under normal traffic and is level with the top of the frame  505  and surface grade  507 . If cover  503  does not fit securely, cover  503  and venting structure  10  are removed from frame  505 . Sealing element  511  is installed on flange  508  to improve the fit of cover  503  to frame  505 . A gasket with an “L”-shaped cross-section is generally preferred for use as sealing element  511 . A caulking substance or packing material may be preferred for use as sealing element  511  if the frame or cover are corroded or worn, or if other field conditions warrant their use. Venting structure  10  then is replaced onto flange  508  and cover  503  is lowered onto frame  505 . If excess material from venting structure  10  protrudes above cover  503 , it can be pushed into the space between cover  503  and frame  505 , cut away, or secured to frame  505  or surface grade  507  with tar or some other suitable sealing material. Preferably, vent holes  504  are sealed, and pick hole  506  is left open to allow ventilation of the gases that pass through sheet  19 . 
     A completed installation is illustrated in FIG.  9 . The edges of venting structure  50 , a structure of the same general type as venting structure  10  and  40 , are squeezed between cover  303  and the inner flange  308  of frame  305  forming a water tight seal. Stiffening ring  55  aids in forming this seal, as does sealing element  311 . Liquid  320  that infiltrates cover  303  is captured and contained between cover  303  and venting structure  50  until liquid  320  evaporates. If the space between cover  303  and venting structure  50  is filled, additional amounts of liquid will be diverted, and will follow the grade  307  to an existing storm water collection system. The presence of excess material  58  between cover  303  and frame  305  does not interfere with opening and closing manholes of conventional design. The manhole is easier to open because excess material  58  blocks dirt from entering the spaces between the manhole frame and cover, which would otherwise cause those parts to bind to each other. It also will prevent metal-on-metal contacts from binding. 
     Installation of venting structures  10  and  40  may become difficult under windy conditions because of the light weight and relatively large surface area of this type of structure. Such conditions can be accommodated by removably securing the venting structure to the frame before lowering the cover onto the frame. Preferably, the venting structure is secured to the frame by applying an adhesive or other tacky substance to the frame and pressing the venting structure into place. Most preferably, the tacky substance is of a type that will the venting structure to be easily removed from the frame to obtain access to the manhole. 
     The conventional practice has been to replace manhole covers by inserting a tool through pick hole  306  and dragging the cover into position on frame  305 . Using this method with installations such as those shown in FIGS. 6 and 7 creates a risk of damaging the venting structure if the cover is carelessly handled or rests loosely in the frame. Hoists and other machines have been used to lower covers onto frames where careful or accurate placement are needed, but such equipment can be cumbersome to move between manholes. Applicant has discovered that manhole covers can be carefully and accurately placed onto their frames using ribbons of the same materials used to make the venting structures. Two or more ribbons are cut from a sheet of water-proof, gas-permeable material having sufficient tensile strength for this purpose. The ribbons are laid onto a level surface and the manhole cover placed across the ribbons. Two persons can then lift the cover and carefully lower it into position on the frame using the ends of the ribbons as handles. After the cover is seated on its frame, the ribbon ends are cut away or secured to the surface grade. This method also allows careful placement of the cover and venting structure as a unit, providing another approach to installing venting structures under windy field conditions. The venting structure is secured to the cover, using a tacky substance, elastic bands, or some other suitable method, and the assembly is placed across the ribbons. The ribbons are then used as handles to lift the cover and venting structure as a unit and lower it into position. 
     A functional venting structure may be assembled in the field from a single sheet of water-repellent, gas-permeable material. In this method, the frame and cover are cleaned according to the method already described. The sheet of material  60  is placed across the access opening  401  defined by frame  405 , after applying sealing elements  411 , if needed, and the cover  403  is lowered into place so that sheet  60  remains smooth and flat on top of flange  408 , and is held securely by the weight of cover  403 . Alternatively, sheet  60  may be placed on a level surface, cover  403  placed on sheet  60 , and sheet  60  and cover  403  positioned over frame  405  and lowered together onto frame  405  using the excess material of sheet  60  that extends around cover  403  as handles to manipulate sheet  60  and cover  403  together. The assembly is then inspected and the installation repeated as has been described. Excess material overlapping frame  405  then is folded back into the space between the cover  403  and frame  405 , cut away or secured to frame  405  or surface grade  407  using tar or by some other suitable sealing material. Preferably, the excess material is folded over a loop  69  of material that fits snugly to the vertically extensive edge of cover  403  to form a double-layer  68  of material. Loop  69  may comprise wire, cord, elastic, or other element of similar shape. Loop  69  provides structural support to sheet  60  and aids in forming a seal between cover  403  and frame  405 . 
     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.