Abstract:
An integrally formed riser pan member for use as a modular component within an access passageway for an on-site waste disposal system, such as a septic tank, to receivably retain a secondary cover member within, the riser pan member including a cylindrical body having an upper portion having a vertical wall member adapted to receive another modular passageway component thereon, and a lower portion which includes an integral pan portion to seatably receive a secondary cover member. The riser pan member further includes an annular ring between the upper and lower portions. The riser pan member can be employed as a lowermost, a highermost, or as an intermediate component in, for example, an access passageway formed of multiple stackable riser members. In addition, the riser pan member may be formed integrally with a stackable riser member.

Description:
REFERENCE TO RELATED APPLICATIONS  
       [0001]    This disclosure is entitled to the benefit of the filing date of U.S. Provisional Application No. 60/353,620, filed Feb. 1, 2002, as to all subject matter commonly disclosed therein. 
     
    
     
       BACKGROUND  
         [0002]    1. Field of the Invention  
           [0003]    This disclosure relates generally to access covers for septic tanks and generally vertical access passageways between a septic tank (or another underground on-site waste disposal system or drainage collection system component) and grade level, and more specifically, to a component for use with (or without) a passageway formed by multiple stackable riser members, which component is capable of being cast into a concrete septic tank top, as well as being stackable with one or more riser members, and removably accepting a concrete or other heavy material cover or inspection lid therein, as well as being adapted to removably accept another cover thereon.  
           [0004]    2. Description of the Prior Art  
           [0005]    An important consideration in the construction of septic tanks and other underground waste or drainage systems is how to provide water tight access to the buried system components for purposes of periodic maintenance (such as for pumping out a septic tank, which is typically done at least every few years, and in some cases, annually or even more frequently). Often, septic tanks and other underground liquid waste-holding components are provided with precast concrete covers, preferably with lift handles cast therein, in order to gain access to the interior of the septic tank. The concrete cover is typically located in the concrete top section, or lid, of the septic tank.  
           [0006]    There have been problems related to the use of make-shift access passage assemblies, such as modified chimney flues made of clay tile or cement, or extended lengths of large diameter pipe (such as smooth-walled PVC pipe, or corrugated or co-extruded pipe), used to form passageways between septic tanks and grade level. In order to overcome problems associated with such make-shift assemblies, a favorable alternative has been developed in the form of durable stackable riser members, as typified by the riser members disclosed in U.S. Pat. Nos. 5,617,679 and 5,852,901, owned by Tuf-Tite, Inc., the assignee of the present invention. Such riser members are typically made of comparatively lightweight, but sturdy material, such as polyethelene. Such injection-molded stackable risers allow for easy adjustment of the overall height of the access passageway, since additional risers can be easily added to increase the height, or risers can be removed to shorten the passageway. In a preferred manner of using these stackable riser members in conjunction with concrete septic tanks, the lowermost riser member is cast directly into the concrete top of the septic tank form. In this manner, perpendicularity of the entire access passageway, formed by a stack of risers, to the top of the septic tank is reliably established and maintained.  
           [0007]    As disclosed in U.S. Pat. No. 5,852,901, the riser members can be interconnected by means of a generally inverted U-shaped connecting member or channel provided at a lower end of the riser member, which is adapted to receive a free upper end of a next-lower riser member in a given stack of risers.  
           [0008]    It is recognized that later-developed riser members, such as the stackable riser sold by Polylok, Inc. and United Concrete Products, Inc. of Yalesville, Conn., employ variations of technique of interconnection of the riser members disclosed in U.S. Pat. No. 5,852,901. For example, as described in U.S. Pat. No. 6,484,451, the risers employ a channel end and an opposite tapered or straight end. The channel end of the riser member includes a middle wall, with notches or slots at regular intervals therein, defining two concentric channels. In a cylindrical stackable riser of the type disclosed in that patent, the middle wall is essentially an interrupted ring. The outermost channel receives the tapered or straight end of the next-lower stackable riser member, and the inner channel of the channel end, together with the notches in the middle wall of the channel end, receive vertical reinforcing ribs provided on the interior wall of the next-lower stackable riser member.  
           [0009]    Access passageways formed by stackable risers, such as those described in U.S. Pat. No. 5,852,901 of Tuf-Tite, Inc., are known to be used in conjunction with an injection molded cover used at grade level. The injection molded cover can terminate a stack of risers by being placed on the uppermost riser in the same manner of interconnection as the other risers, e.g. by an inverted U-shaped channel extending downwardly from the cover.  
           [0010]    The cover is secured to the uppermost riser by, for example, securement screws and screws which extend vertically through the cover at its perimeter, and which are received in screw bosses provided around the exterior of the uppermost riser in a stack of risers, all for safety and security reasons. Such covers are preferably provided with additional horizontally-oriented securement screws, screws, or other fasteners, which extend in a direction perpendicular to the vertically-extending securement screws. Instead of being received in screw bosses, these lateral securement screws may abut the upper lip of the uppermost riser which is received in a channel provided in the bottom of the cover, or alternatively, extend through screw holes provided in the upper lip of the uppermost riser in a stack of risers. Even with such securement methods available for the injection-molded covers, there exists a need for an additional cover in the form of a heavy-duty concrete (or other heavy material) secondary cover provided either just below the injection molded cover, i.e. at or near grade level, or alternatively, in or immediately adjacent to the concrete lid of the septic tank, i.e. at or near the bottom of the passageway.  
           [0011]    Those of ordinary skill in the art will understand that the term “concrete lid” of the septic tank refers to the large, horizontally-oriented concrete slab, typically on the order of 4 feet by 8 feet, for example, provided at the top of the septic tank having a capacity from about 750 to about 1,250 gallons, and supported by the walls of the septic tank, as opposed to the term “concrete cover”, which as used herein, refers to the well-known removable, generally smaller (and typically round) cover member associated with an opening in the concrete lid and used to gain access to the interior of the septic tank. Such concrete covers are generally flat, have cylindrically-shaped outer peripheral walls, while others may be tapered, and may include a stepped portion. The concrete covers sit atop the concrete lid, over the lid&#39;s access opening. These concrete covers allow a point of access to the interior of the septic tanks for drainage, cleaning, or other maintenance, including access to effluent filters provided at the inlet or outlet of the septic tank, for cleaning or replacement of the filters. Even in instances where a covered access passageway is provided over the concrete lid of the septic tank, there is a growing need for such secondary concrete or other heavy material covers over the lid&#39;s access opening in order to comply with many existing and imminent state and local regulations requiring such covers, as well as for added safety considerations. In those localities where there are no regulations requiring covers of a particular material or weight, it is still beneficial to use an internal cover within a septic tank or other on-site waste system access passageway, even if the cover is made of a lightweight material, such as plastic.  
           [0012]    It is recognized that conventional on-site waste system access passageways formed of extended lengths of PVC pipe have been outfitted with plastic or fiberglass covers, often secured to the top of the PVC pipe by screws. However, such arrangements are considered even less secure than the stackable risers with injection-molded covers. Further, the PVC pipe passageways, which typically have smooth inner walls, do not provide any means for accepting and retaining secondary concrete or other heavy material septic tank covers, either at or near grade level, or lower down in the passageway.  
           [0013]    One difficulty relating to the use of concrete covers in the lid of the septic tank, especially in combination with such passageways formed by stackable risers, occurs when the concrete cover is cast in place in the concrete lid of the septic tank. Such covers are typically formed in a steel forming pan used repeatedly by a concrete pre-caster, for the sole purpose of casting concrete covers. The installer has little room in which to cast the lowermost riser in place around the pre-cast concrete cover. Due to such space considerations, the casting of a concrete lid for a septic tank with a cast-in lowermost riser is often achieved using several separate pouring operations. First, a lowermost riser is placed on the floor and a steel pan is placed therein. Next, concrete is poured in the space between the outside of the steel pan and the inside of the lowermost riser. After that, concrete is introduced into the inside of the steel pan to form the concrete cover. The steel pan is often frustro-conical in shape, with a lower end having a smaller diameter than the upper end. Before the concrete cover dries, it is desirable to add a cast-in handle, such as the H1 “Cast In Handle” available from the present assignee, Tuf-Tite, Inc., i.e. to the center of the concrete cover to facilitate removal and replacement of the cover. Finally, concrete can be poured to form the concrete lid of the septic tank around the outside of the lowermost riser, thereby encasing and retaining the lowermost riser within that concrete lid.  
           [0014]    The concrete cover is removed from the ring of concrete formed in the interior of the lowermost cast-in-place riser, and the steel pan is removed for re-use. Due to the frustro-conical shape of the pan, once the steel pan is removed, the resulting concrete cover has a frustro-conical profile which can then be placed over the complementary concrete ring formed in the interior of the lowermost stackable riser, which serves as a mating angled seat for the concrete cover. There is a tendancy for there to be a mismatched fit, which results in a locking wegde fit between the concrete cover and the complementary concrete ring, which is undesirable.  
           [0015]    At least one such stackable riser, such as is available from Tuf-Tite, Inc., includes an interiorly-extending annular ring, which provides some internal support for the concrete interior ring. However, due to the relatively narrow width of the concrete ring within the concrete riser, there is some concern about degradation of the concrete seat for the concrete cover. Over the years, repeated access to the septic tank via the concrete cover may tend to cause chips or cracks in the concrete seat, particularly if people accessing the tank drop the concrete cover in place from any significant height above the top of the septic tank, as is not uncommon due to both the weight of the concrete cover and the depth of some septic tanks.  
           [0016]    It would be desirable if the lowermost, cast-in-place riser could also form the mold pan for the concrete cover and also remain in place as the seat for the concrete cover when the concrete septic tank lid is installed underground on a septic tank. This approach would advantageously avoid the need for a separate steel form pan, reduce the number of pouring operations during casting, and add reliability to the resulting seat for the concrete cover. The manner in which these and other benefits of the present invention are achieved will be explained in greater detail in the following Detailed Description of the Invention and the drawings. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 is a perspective view of a riser pan of a first embodiment of the present invention;  
         [0018]    [0018]FIG. 2 is a perspective, partially exploded view of the riser pan shown in FIG. 1, in combination with a pair of stackable risers and a cover for use at grade level;  
         [0019]    [0019]FIG. 3 is a front elevation view of the riser pan shown in FIG. 1;  
         [0020]    [0020]FIG. 4 is a bottom perspective view of the riser pan shown in FIG. 1;  
         [0021]    [0021]FIG. 5 is a bottom plan view of the riser pan shown in FIG. 1;  
         [0022]    [0022]FIG. 6 is a cross-sectional view of the riser pan shown in FIG. 1, taken along lines  6 - 6  of FIG. 1;  
         [0023]    [0023]FIG. 7 is an environmental cross-sectional view of the riser pan, stackable riser, and cover combination shown in FIG. 2, with the riser pan cast into a concrete lid of a septic tank, and showing a cross section of a concrete cover received in the riser pan;  
         [0024]    [0024]FIG. 8 is a perspective environmental view, partially broken away and exploded, of a riser pan of the type shown in FIG. 1, cast-in-place into a concrete lid of a septic tank, and positioned over the outlet port of the septic tank, and without any additional riser components, but with an injection-molded cover for the riser pan, a concrete cover to be received in the riser pan, and a sealing gasket to be received between a flat portion of the concrete cover and a flat portion of the riser pan to form a substantially liquid-tight seal between the concrete cover and the riser pan;  
         [0025]    [0025]FIG. 9 is an enlarged cross-sectional view, broken away, taken along circular line  9  in FIG. 6, of the riser pan of FIGS.  1 - 8 ;  
         [0026]    [0026]FIG. 10 is a perspective, partially exploded view of a riser pan of the type shown in FIG. 1, in combination with a pair of stackable risers and a cover for use at grade level, depicting placement of the riser pan in an alternate position (i.e. higher in a stack of risers than is shown in FIG. 2);  
         [0027]    [0027]FIG. 11 is a perspective view, partially broken away, of a second embodiment of the riser pan, wherein the riser pan is formed as an integral part of a stackable riser member;  
         [0028]    [0028]FIG. 12 is a cross-sectional view of the second embodiment riser pan of FIG. 11, taken along lines  12 - 12  of FIG. 11, with cross-sections of a portion of the two conventional risers immediately above and below the riser pan shown in phantom lines for better viewing;  
         [0029]    [0029]FIG. 13 is a bottom perspective view of the alternate riser pan shown in FIG. 11;  
         [0030]    [0030]FIG. 14 is an exploded perspective view of the alternate riser pan shown in FIG. 11 in combination with an injection-molded cover for the riser pan;  
         [0031]    [0031]FIG. 15 is an exploded perspective view of a third embodiment of the riser pan in combination with another form of existing prior art stackable riser member, and additionally showing in phantom lines alternate, more preferred positions for the exterior annular ledge of the riser pan and for the stackable riser;  
         [0032]    [0032]FIG. 16 is a perspective view of the alternate riser pan and prior art stackable riser combination shown in FIG. 15, and also showing in phantom lines alternate, more preferred positions for the exterior annular ledge of the riser pan and for the stackable riser;  
         [0033]    [0033]FIG. 17 is an exploded perspective view of the alternate riser pan and prior art stackable riser combination shown in FIG. 15, with the relative positions of the riser pan and stackable riser reversed, depicting this third embodiment of the riser pan stacked above the prior art stackable riser;  
         [0034]    [0034]FIG. 18 is a cross-sectional view, broken away, of the alternate riser pan and stackable riser combination shown in FIG. 17;  
         [0035]    [0035]FIG. 19 is a cross-sectional view, broken away, of the alternate riser pan and stackable riser combination shown in FIGS. 15 and 16;  
         [0036]    [0036]FIG. 20 is a perspective view of a fourth embodiment of the riser pan, as integrally formed with the alternate type of riser member shown in FIG. 15;  
         [0037]    [0037]FIG. 21 is a cross-sectional view, broken away, of the alternate riser pan and riser integral combination as shown in FIG. 20;  
         [0038]    [0038]FIG. 22 is a perspective view of a riser pan of a fifth embodiment of the present invention;  
         [0039]    [0039]FIG. 23 is a cross-sectional view of the riser pan shown in FIG. 22, taken along lines  23 - 23  of FIG. 22;  
         [0040]    [0040]FIG. 24 is an enlarged cross-sectional view, broken away, taken along circular line  24  in FIG. 23 of the riser pan of FIGS. 22 and 23;  
         [0041]    [0041]FIG. 25 is a perspective view of a riser pan of a sixth embodiment of the present invention;  
         [0042]    [0042]FIG. 26 is a cross-sectional view of the riser pan shown in FIG. 25, taken along lines  26 - 26  of FIG. 25;  
         [0043]    [0043]FIG. 27 is an enlarged cross-sectional view, broken away, taken along circular line  27  in FIG. 26 of the riser pan of FIGS. 25 and 26;  
         [0044]    [0044]FIG. 28 is a perspective view of a riser pan of a seventh embodiment of the present invention;  
         [0045]    [0045]FIG. 29 is a cross-sectional view of the riser pan shown in FIG. 28, taken along lines  29 - 29  of FIG. 28; and  
         [0046]    [0046]FIG. 30 is an enlarged cross-sectional view, broken away, taken along circular line  30  in FIG. 29 of the riser pan of FIGS. 28 and 29, and showing a cross-section of a sealing gasket provided on the interior of the riser pan. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0047]    A first embodiment of a riser pan  10  for use in conjunction with an access passageway formed of stackable, interconnecting risers  12 ,  14  is shown in FIGS.  1 - 10 . In a preferred embodiment, the riser pan  10  takes the form of an injection-molded cylindrical member made of high density polyethylene. More specifically, the riser pan  10  includes an upper cylindrical wall  16 , a lower pan portion  18 , and an intermediate, generally flat annular ring  20 . The pan portion  18  is preferably frustro-conical, has a lowermost edge  22  and an upper end  24 . The frustro-conical pan portion  18  is tapered inwardly, such that its diameter at the lowermost edge  22  is less than at the upper end  24 . In a preferred embodiment of the riser pan  10 , the degree of taper of the pan portion  18  is in the range of between approximately 0° and 45°, and preferably about 14.796° for a 24″ riser pan, but those of ordinary skill in the art will appreciate that an even wider range of angles for the taper are possible, and even varying angles within the length of the taper so as to impart a curvilinearly-profiled surface to the frustro-conical pan portion  18 , and all are within the scope of the present invention. While the incline of the frustro-conical pan portion  18  preferably extends substantially the entire height of the pan portion  18 , alternatively, and also within the scope of the present invention, the pan portion  18  could include both generally vertical and generally inclined portions so as to form a stepped profile within the pan portion  18 . In the event a stepped profile is employed, it is further recognized that the degree of incline of the inclined portions may differ from one another to facilitate removal of a cover cast within the riser pan, among other benefits.  
         [0048]    Preferably, as best seen in FIGS. 1 and 9, the riser pan  10  is provided with a standing circular rib  15  having a generally vertical outer surface  17  and an inner surface  19  that is preferably slightly tapered or inclined. Inasmuch as the standing circular rib  15  allows a concrete or other material cover to have a stepped profile, as discussed below, the degree of taper of the pan portion  18  may be 0° without causing the cover to fall through pan portion  18 . The degree of incline of the inner surface  19  of the standing circular rib  15  is preferably in a range of about 0° (i.e., vertical) to about 5° from vertical with respect to the generally flat annular ring  20  of the riser pan  10 . However, it is recognized that other degrees of incline for inner surface  19  are possible. The preferred subtle incline to the inner surface  19  of the standing circular rib  15  advantageously facilitates proper centering and alignment of a concrete or other heavy material cover  58  (see FIG. 7; discussed in more detail below). It is recognized that while the internal cover  58  disclosed herein is described as being made of concrete or other heavy material, it is also within the scope of the present invention to use an internal cover made of a lightweight material, such as injection molded plastic.  
         [0049]    The portion of the generally flat annular ring  20  between the upper end  24  of the frustro-conical pan portion  18  and the standing circular rib  15  provides a circular, generally flat, step  21 . In those applications in which a cover  58  is taller than the frustro-conical pan portion  18 , i.e. where the cover  58  extends further up into the region of the riser pan  10  defined by the standing circular rib  15 , the step  21  advantageously provides a generally flat interface between the cover  58  and the riser pan  10 . Inasmuch as obtaining a water-tight seal is significantly more difficult between inclined, as opposed to flat, surfaces, it is preferable that any means for providing or enhancing a water-tight seal between the riser pan  10  and the cover  58  be accomplished in the area of the step  21 .  
         [0050]    For example, an O-ring or generally flat annular sealing ring gasket  61  may be provided on the step  21  to form a substantially water-tight seal between the riser pan  10  and a cover  58  received therein. By way of example only, the inner side  19  of the standing circular rib  15  may be horizontally spaced anywhere from ¼-inch from the upper end  24  of the frustro-conical pan portion  18  to a location ¼-inch inwardly from the outer wall, and the standing circular rib  15  may have a height of {fraction ( 1 / 2 )}-inch to 1 inch, preferably ¾-inch, but may be made taller or shorter, if desired, by the manufacturer. The standing circular rib  15  may also be spaced closer to or farther from the upper end  24  of the frustro-conical pan portion  18 , if desired by the manufacturer.  
         [0051]    The generally flat annular ring  20  preferably extends radially outwardly from the upper end  24  of the frustro-conical pan portion  18  past a lower end  26  of the upper cylindrical wall  16 , and terminates at an outer edge  28  which is outside the upper cylindrical wall  16 . Thus, an annular ledge  30  is provided around the exterior of the lower edge  26  of the upper cylindrical wall  16 , which, in this first embodiment, co-extends with the surface provided inside the upper cylindrical wall  16  by the generally flat annular ring  20 . The upper cylindrical wall  16  terminates at an upper end  25 .  
         [0052]    The annular ledge  30  provides a useful gripping portion for use during installation of the riser pan  10  when placed onto a passageway  31  of stackable risers  12 ,  14  (see FIG. 2) at a location other than its most preferred cast-in location at the concrete lid section of the septic tank. Also, while being buried in the ground as part of such a passageway  31  formed, at least in part, by stackable risers  12 ,  14  and the riser pan  10 , the backfill (not shown) rests upon the annular ledge  30  to help hold the riser pan  10  in its position relative to the stackable risers  12 ,  14 , thereby improving the lateral stability of the entire passageway  31 . Furthermore, the backfill also tends to exert downward loads on the annular ledge  30 , which tends to push the riser pan  10  down toward other stackable risers (not shown in FIG. 2) that are interconnected in the passageway beneath the riser pan  10 . As discussed in U.S. Pat. No. 5,852,901, which is incorporated herein by reference, the stackable risers  12 ,  14  are provided with horizontal, outwardly-extending annular ledges  29 , which provide a similar function. As seen in FIGS. 2 and 10, the stackable risers  12 ,  14  may each include a plurality of such outwardly-extending annular ledges  29 , as the ledges  29  advantageously improve rigidity of the risers  12 ,  14 , and thereby increase the rigidity of the entire passageway  31 .  
         [0053]    This first embodiment of the riser pan  10  further includes a plurality of exterior, vertically-oriented ribs  32  extending above the annular ledge  30  along the outside of the upper cylindrical wall  16 , which are provided to help distribute load transmitted to the riser pan  10  from a next-higher riser  12  stacked thereon. In addition to the ribs  32 , several screw bosses  33 , each having sidewalls  34 ,  36 , an inner wall defined by an outer portion of the upper cylindrical wall  16 , and an outer wall  37 , are provided at periodic locations about the upper cylindrical wall  16 , which also extend above the annular ledge  30 . These screw bosses  33  may take the form of a pair of closely-spaced ribs which are adapted to securely receive a threaded screw therebetween, but it is preferred that the screw bosses  33  be enclosed on the bottom and sides thereof, so as to prevent dirt or, more importantly, concrete (when the riser pan  10  is cast into a concrete septic tank lid), from entering the screw bosses  33  and obstructing the screw-receiving opening therein. Preferably, the screw bosses  33  may be hollow cylindrical or, in the embodiment shown, substantially rectangular hollow polygonal members. The purpose of such screw bosses  33  is to enable securement of an injection molded polyethelene riser cover  38  directly to the top of the riser pan  10  or riser  12 ,  14 , if it is desired to place a riser pan  10  at or near grade level, i.e. at the top of a passageway  31 , as shown in FIG. 10. The screw bosses  33  need not be internally threaded to faciltitate securely receiving a threaded screw therein, inasmuch as the opening within the screw bosses  33  is sized so as to become self-threading, i.e. the threads of the securement screws will cut into the interior walls of the screw bosses  33  upon initial securement of the molded cover  38  thereon.  
         [0054]    Additional screw bosses  35  are also preferably provided, which are spaced apart from the screw bosses  33 . These additional screw bosses  35  extend downwardly from the annular ledge  30 . Like the screw bosses  33 , these additional screw bosses  35  are preferably enclosed, aside from the screw-reciving bore therein, to prevent dirt or concrete from interfering with or corroding a screw (not shown) received in the additional screw boss  35 . Because the additional screw bosses  35  are spaced from the screw bosses  33 , it will be recognized that screw bosses  33  will also be out of alignment with screw bosses  33   r  of an adjacent riser  12  to which the riser pan  10  is secured, as shown in FIG. 10. Instead, the screw received in the additional screw boss  35  is received in the screw boss  33   r  aligned with the additional screw boss  35 .  
         [0055]    It is recognized that there are often instances where a septic tank may be buried such that its concrete lid is just below grade level. As shown in FIG. 8, the riser pan  10  advantageously facilitates the use of two covers, one being the injection-molded cover  38  secured to the top of the upper cylindrical wall  16  of the riser pan  10 , and the other being a cover  58  (shown in FIG. 7) made of concrete (or some other heavy material) fitting within the frustro-conical pan portion  18 , in such applications where there is essentially no room for the use of access passageways such as those formed by the use of multiple interconnected stackable risers  12 ,  14 . When the cover  58  is made of concrete, which is typically the case, such a concrete cover  58  may advantageously be cast directly in the riser pan  10 , thereby avoiding the need for a separate mold for casting the concrete cover  58 . It is recognized that there are applications in which the concrete or other heavy material cover  58  is adequate, and no external injection molded cover need be used.  
         [0056]    As best shown in FIGS. 4, 6 and  9 , the underside of the riser pan  10  includes a channel  40 , generally of an inverted U-shape in cross-section, which extends downwardly from the generally flat annular ring  20  and ledge  30 . The channel  40  has legs or sidewalls  42 ,  44 , which extend generally about the entire periphery of the riser pan  10 . As described in more detail in certain other embodiments discussed below, it is recognized that these legs or sidewalls  42 ,  44 , while preferably continuous to provide optimum water tightness, could be interrupted legs or sidewalls without departing from the scope of the present invention. The channel  40  may be advantageously sized to receive an uppermost male edge  46  of a complementary riser  14 , in applications where it is desired to stack the riser pan  10  higher in a passageway  31 , rather than the riser pan  10  being cast, as at a lower level, into the concrete septic tank lid  56 .  
         [0057]    It is recognized that the sidewalls  42 ,  44  of the channel  40  may alternatively be spaced apart any desired distance by the manufacturer, so as to accommodate more conventional access passageway components, such as corrugated pipe or smooth-walled PVC pipe of a given diameter. Thus, the riser pan  10  of the present invention can be used to cap off existing access passageways or flues with both an injection-molded, securely screwed riser cover  38 , and also accommodate a secondary concrete cover just below grade level, as may be highly desirable to increase the safety of existing septic tank installations. It can be used as well to bring (i.e., retrofit) such existing in-ground waste systems into compliance with newer state and/or local regulations requiring multiple covers to septic tank access openings.  
         [0058]    Another application wherein the riser pan  10  may be used to retrofit an existing access passageway is a passageway  31  formed by a plurality of stackable risers. A homeowner desiring to install a secondary cover would simply remove the uppermost riser  14  of the existing access passageway and replace it with a riser pan  10 . The riser pan  10  would accommodate both a concrete or other heavy material cover  58  in its frustro-conical pan portion  18 , as well as a securely-screwed injection molded outer primary cover  38  on its upper cylindrical wall  16 . Yet another potential application for the riser pan  10  is in an access passageway formed entirely of cylindrical concrete segments. Advantageously, one could cast the riser pan  10  such that it is sandwiched between two cylindrical segments within the passageway, i.e. two risers  12 ,  14 , thus providing a means, by way of the frustro-conical pan portion  18  of the riser pan  10 , to use a secondary concrete or other heavy material cover  58  at a desired height within the access passageway.  
         [0059]    Most preferably, the sidewalls  42 ,  44  of the inverted, U-shaped channel  40  are of equal length, i.e. height, to one another. It is found that, when casting the riser pan  10  into the concrete form of the septic tank lid, concrete can flow horizontally when riser pan  10  sits on top of the concrete lid form for the septic tank. This allows the concrete to fill any voids under the inverted, U-shaped channel  40 . Alternatively, if the sidewalls  42 ,  44  were of different heights, for example if the inner sidewall  42  were taller than the outer sidewall  44 , the concrete would have difficulty flowing around the inner sidewall  42 , and there would most likely be undesirable voids left between the riser pan  10  and the concrete lid of the septic tank. Also, with a taller internal sidewall  42 , there is less even distribution of vertical loads coming down through the passageway  31 .  
         [0060]    [0060]FIG. 4 also shows the presence of additional ribs or gussets  48 , which are preferably provided at regular intervals, in this first embodiment of the riser pan. These gussets  48  extend from the inner sidewall  42  of the channel  40 , along the underside of the generally flat annular ring  20 , and down along the outside of the frustro-conical pan portion  18 , terminating at the lowermost edge  22  of the frustro-conical pan portion  18 . The gussets  48  help maintain the rigidity of the frustro-conical pan portion  18 , and increase the stability of the frustro-conical pan portion  18 , which is advantageous inasmuch as the frustro-conical pan portion  18  is intended to support a secondary concrete or other heavy material septic tank cover  58  therein. It is recognized that the septic tank cover  58  may be made of a suitably strong material other than concrete, although concrete is, desirable for its weight and is an approved material for use as a septic tank cover in many jurisdictions.  
         [0061]    In order to provide even additional stability to the frustro-conical pan portion  18  for the riser pan  10 , it will be appreciated by those of ordinary skill in the art that the gussets  48 , which appear in FIG. 4 to terminate at a flat edge  50  along the bottom of the generally flat annular ring  20 , actually extend above the generally flat annular ring  20 . Turning back to FIG. 1, there can be seen a plurality of gusset extensions  52 , disposed in the embodiment shown in 45° intervals, which extend from the gussets  48  directly opposite each respective gusset extension  52  on the opposite side of the generally flat annular ring  20 . These gusset extensions  52 , which extend up the inside of the upper cylindrical wall  16  and terminate along the outside of the standing circular rib  15 , help distribute loads exerted on the frustro-conical portion to the upper cylindrical wall  16 . The gusset extensions  52  also reinforce the standing circular rib  15 ; the extensions  52  advantageously help resist damage to the standing circular rib  15  as a heavy cover  58  is repeatedly inserted in and removed from the riser pan  10 .  
         [0062]    The gusset extensions  52  may be further reinforced by the vertically oriented ribs  32 , some of which are directly opposite the upper cylindrical wall  16  from respective gusset extensions  52 . Advantageously, the gusset extensions  52  are preferably each provided with a flat top  53  (see FIGS. 6 and 7), which can accommodate, and thereby help support, an inner sidewall  54  of an inverted generally J-shaped channel extending downwardly from either a stackable riser  12 ,  14  or a cover  38 . That is, the vertically oriented ribs  32  on the outside of the upper cylindrical wall  16  preferably terminate, in this first embodiment of the riser pan, an appropriate distance from the upper end  25  of the upper cylindrical wall  16 , so that the outer sidewall  55  of the J-shaped channel of either a stackable riser  12 ,  14  or cover  38  rests thereon. (See FIG. 7) Thus, the flat top  53  of the gusset extensions  52 , the upper end  25  of the upper cylindrical wall  16 , and the tops of the vertically oriented ribs  32  all preferably cooperate to distribute vertical loads imparted to the riser pan  10  from stackable risers  12 ,  14  and/or the molded riser cover  38 . The U-shaped channel  40  of the riser pan  10  also enables multiple riser pans  10  to be vertically nested together for storage, shipping, or retail display, and alternatively, to be nested with and between riser members  12 ,  14  at any desired location within the stack.  
         [0063]    Advantageously, several riser pans  10  may be cast into a single concrete septic tank lid  56  at different locations therein. For example, one of the riser pans  10  (not shown in FIG. 8) can be cast into the concrete tank lid  56  such that it is positioned over the septic tank inlet, a second riser pan  10  can be cast into the concrete lid  56  over the outlet of the septic tank (as shown in FIG. 8), and, for optimal access and so as to facilitate pumping out the septic tank, a third riser pan  10  (also not shown in FIG. 8) could additionally be cast into the concrete lid  56  so that it is generally centrally positioned over the septic tank to provide interior access.  
         [0064]    Typically, the concrete lid  56  of a septic tank has a thickness in a range from about 2-{fraction ( 1 / 2 )} inches to about 4-{fraction ( 1 / 2 )} inches. It will be recognized that neither the overall height of the riser pan  10 , nor the height of the screw bosses  33 , need to constitute a limit on the thickness of the concrete lid  56  into which the riser pan  10  can be cast. In the event one desires to cast a riser pan  10  into a concrete septic tank lid  56  of greater thickness than the height of the screw bosses  33 , an appropriately-sized shim (not shown), made, for example, of wood or foam, can be placed beneath the riser pan  10  during casting so as to raise the riser pan  10  a desired distance, such that the top of the screw bosses  33 , if desired, can be kept level with, or higher than, the top of the concrete septic tank lid  56 . It will be recognized that in such an installation, the resulting concrete cover  58  would have the thickness of the frustro-conical section of the riser pan  10 , so the concrete cover  58  would not necessarily extend completely to the bottom of the concrete tank lid  56 .  
         [0065]    When casting the riser pan  10  into a concrete tank lid  56 , the tops of the screw bosses  33  are exposed, so that an injection-molded cover  38  can be securely screwed directly to the riser pan  10 , as would occur once the injection molded cover  38  shown in FIG. 8 is seated on the top of the cast-in-place riser pan  10 . This is particularly desirable in instances where, as discussed above, the concrete septic tank lid  56  is just below grade level, so that two covers  38 ,  58  can be used with such a septic tank. However, even in instances where the septic tank is deeply buried, and there is an elongated access passageway  31  formed of multiple stackable risers  12 ,  14 , it is still desirable to have the screw bosses  33  exposed, inasmuch as there may, for example, become a need to remove the passageway  31 , leaving the septic tank buried, and it would be desirable to cap-off the septic tank with both a concrete cover  58  and an injection-molded cover  38  prior to filling in the hole left by the removed components which formed the passageway  31 .  
         [0066]    It is also preferable to cast the concrete cover  58  so as to not only fill the frustro-conical pan portion  18 , but also to fill (at least partially, but preferably, completely) the slightly higher region of the riser pan  10  bounded by the inner surface  19  of the standing circular rib  15 . As shown in FIGS. 7 and 8, the resulting concrete cover  58  has a double-tiered shape having an upper tier  57  that is complementary to the region of the riser pan  10  bounded by the inner surface  19  of the standing circular rib  15  (which, as indicated above, is at least slightly inclined) and the step  21 , and then a lower tier  59  that is complementary to the frustro-conical pan portion  18 . The essentially stepped, double-tiered shape of the concrete or other heavy material cover  58  advantageously assists in preventing the cover  58 , once removed from the riser pan  10 , from being crookedly placed back into the riser pan  10 , and from being taper-locked within the pan portion  18 . The incongruity between the relatively shallow slope of the peripheral edge of lower tier  59  of the cover  58  and the relatively steep slope of the inner surface  19  of the standing cylindrical rib  15 , together with gravitational forces, tend to direct the lower tier  59  of the concrete or other heavy material cover  58  into a proper alignment and position within the frustro-conical pan portion  18 , thereby repeatedly facilitating proper centering and positioning of the concrete or other heavy material cover  58  within the riser pan  10 . In instances where an O-ring or annular sealing gasket  61  is provided on the step  21 , the proper centering and positioning of the cover  58  within the riser pan  10  improves the integrity of the liquid-tight seal between the cover  58  and the riser pan  10 . Alternatively, a sealing tape, a sealing caulk bead, or other suitable sealing means may be used on the step  21  to achieve a substantially liquid-tight seal between the cover  58  and the riser pan  10 .  
         [0067]    The diameter of the passageway  31 , which would preferably be equal to the diameter of the upper cylindrical wall  16 , and the diameters of the openings at the lowermost edge  22  and upper end  24  of frustro-conical pan portion  18  of the riser lid  10 , are all determined by the manufacturer. For example, riser pans  10  may be made with outer diameters of 16 inches, 20 inches, and 24 inches (as these are diameters commonly used in existing cylindrical stackable risers), with corresponding diameters of the respective opening at the lowermost edge  22  of the frustro-conical pan portion  18  being in a range from approximately 12-13 inches, 16-17 inches, and 20-21 inches. The riser pan  10  may have an overall height of about 5 inches, or some other height as selected by the manufacturer, with the height of the upper cylindrical wall  20  being approximately 3 inches, and the height of the frustro-conical pan portion being approximately 2 inches (both given for 5 inch high riser pans, for example).  
         [0068]    The upper end  24  of the frustro-conical pan portion in this first embodiment of the riser pan is, for example, spaced 2-{fraction ( 1 / 2 )} inch from the lower end  26  of the upper cylindrical wall  16 . Each of the screw bosses  34 ,  36  is spaced, in this first embodiment shown, for example, ½ inch from the upper end  25  of the cylindrical wall  16 , such that the height of the top of each of the screw bosses  33  is, for example, 4-{fraction ( 1 / 2 )} inches, as measured from the lowermost edge  22  of the frustro-conical pan portion  18 .  
         [0069]    Turning to FIGS.  11 - 14 , a second embodiment of the riser pan  110  is shown, with like features to those described above with respect to the first embodiment being identified in this embodiment with the same reference number, increased by 100. In the second embodiment, the riser pan  110  shares many of the attributes of a riser  12 ,  14 , as shown in FIGS. 2 and 7, but also includes a frustro-conical pan portion  118 . The riser pan  110  may include one or more horizontal, outwardly-extending annular ribs  129 . The ribs  129  advantageously improve rigidity of the riser pan  110 , and thereby cooperate with adjacently-stacked risers  112 ,  114 , as shown in FIG. 12, to increase the rigidity of an entire passageway  131  of a plurality of risers  112 ,  114  and riser pan  110 .  
         [0070]    Like the annular ledge  29  of the riser pan  10  of the first embodiment, the annular ribs  129  provide a gripping portion to facilitate handling and installation, backfill rests upon the ribs  129  to hold the riser pan  110  in position, while tending to exert downward forces on the ribs  129 , which tend to push the riser pan  110  downwardly toward a next-lower riser  112  in a passageway  131 . The riser pan  110  may further include a plurality of external, vertically-oriented ribs  132  along the outside of an upper cylindrical wall  116  of the riser pan  110 . The vertically-oriented ribs  132  help distribute loads transmitted to the riser pan  110  from a next-higher riser  114 .  
         [0071]    In addition to the ribs  132 , several screw bosses  133 , each having sidewalls  134 ,  136 , an inner wall defined by an outer portion of the upper cylindrical wall  116 , and an outer wall  137 , are provided at periodic locations about the upper cylindrical wall  116 . These screw bosses  133  may take the form of a pair of closely-spaced ribs which are adapted to securely receive a threaded screw therebetween. The screw bosses  133  include an enclosed portion at least near the top opening thereof, extending down to at least an uppermost of the horizontal ribs  129 , as best shown in FIG. 13, so as to prevent dirt or, more importantly, concrete, from entering the screw bosses  133  and obstructing the screw-receiving opening therein. Preferably, the screw bosses  133  may be hollow cylindrical or, in the embodiment shown, substantially rectangular hollow polygonal members. The purpose of such screw bosses  133  is to enable securement of an injection molded polyethelene riser cover  138  directly to the top of another riser (not shown) or to the top of the riser pan  110 , if it is desired to place a riser pan  110  at or near grade level, i.e. at the top of a passageway  131 .  
         [0072]    The screw bosses  133  are sized such that the threads of the securement screw will cut into the interior walls of the screw bosses  133  upon initial securement of the molded cover  138  thereon, as shown in an exploded view in FIG. 14.  
         [0073]    A third embodiment of the riser pan of the present invention is shown in FIGS.  15 - 19 . In the drawing figures depicting this third embodiment, like features to those described above with respect to the first embodiment are identified with the same reference number, increased by 200. The riser pan  210  of this third embodiment, as in the embodiments described above, includes a frustro-conical pan portion  218  to accommodate a concrete septic tank cover of the type shown in FIG. 7 as reference number  58 , and the riser pan  210  is adapted for use with existing prior art stackable risers  212 ,  214 .  
         [0074]    The riser pan  210  has an upper cylindrical wall  216  and between the upper cylindrical wall  216  and the frustro-conical pan portion  218  is an intermediate, generally flat annular ring  220 . Instead of external, vertically-oriented ribs, in this third embodiment a plurality of vertically-oriented ribs  232  are provided on the inside of the upper cylindrical wall  216 . Unlike the gusset extensions  52  (which are shown in FIGS. 6 and 7 to each have a flat top  53  spaced downwardly from the upper end  25  of the upper cylindrical wall  16 , so as to support an inner sidewall  54  of an inverted J-shaped channel at the lower edge of a riser  12 ) and the vertically-oriented ribs  32  of the first embodiment (which terminate some predetermined distance below the upper end  25  of the upper cylindrical wall  16 , and support the outer sidewall  55  of the inverted J-shaped channel of the riser  12 ), the vertically-oriented ribs  232  extend to the upper end  225  of the upper cylindrical wall  216  in this third embodiment.  
         [0075]    The riser pan  210  includes an annular ledge  230  which may co-extend with the surface provided inside the upper cylindrical wall  216  by the generally flat annular ring  220 , like in the first embodiment. However, because there are no external vertically-oriented ribs, in order to strengthen the riser pan  210  it is recognized that it may be preferable to provide the annular ledge at a higher point along the upper cylindrical wall  216 , as shown in phantom lines in FIG. 15 and designated by the reference number  230   a.    
         [0076]    The prior art riser  212  which the riser pan  210  is adapted to receive is provided with an inverted channel with an inner sidewall  254 , an outer sidewall  255 , and intermediate the inner and outer sidewalls  254 ,  255  is an interrupted annular ring  260 . The annular ring  260  is interrupted by a plurality of rib-receiving notches or gaps  262 , spaced to coincide with the vertically-oriented ribs  232 . The vertically-oriented ribs  232  are received in the rib-receiving notches or gaps  262 , thereby interlocking the interrupted annular ring  260  with the vertically-oriented ribs  232  and preventing rotation of the riser pan  210  relative to the riser  212 . Like the annular ledge  230 , it is recognized that the riser  212  may be provided with an external riser ledge  264 . Furthermore, as the riser  212  used in conjunction with the riser pan of this embodiment lacks external vertical ribs, it may be preferable to locate the external riser ledge  264  in a position near the upper end of the riser  212 , such as shown in phantom lines in FIGS. 15, 16 as reference number  264   a.    
         [0077]    Turning to FIG. 17, the underside of the riser pan  210  includes a plurality of gussets  248  extending between the frustro-conical pan portion  218  and an underside of the intermediate, generally flat annular ring  220 . The gussets  248  terminate at an interrupted annular ring  266 . The annular ring  266  is interrupted by a plurality of rib-receiving notches or gaps  268 , spaced to coincide with vertically-oriented ribs  270  located on the the inside cylindrical wall of a riser  214 . An annular wall  272  may also extend downwardly from the annular ledge  230 , spaced outwardly of the interrupted annular ring  266 , forming a channel between the interrupted annular ring  266  and the annular wall  272  to receive an upper edge  274  of the sidewall  276  of the prior art stackable riser  214 .  
         [0078]    As seen in FIGS. 18, 19 the upper edge  274  of the sidewall  276  of the risers  212 ,  214  may be stepped inwardly, i.e. having a reduced thickness as compared to the rest of the sidewall  276 , so that the annular wall  272  forms a continuous wall with the sidewall  276  of the risers  212 ,  214  when stacked to form a vertical conduit or passageway. This will enhance the transfer of vertical loads downwardly through the stack.  
         [0079]    A fourth embodiment of the riser pan is shown in FIGS. 20 and 21. Like features to those described above with respect to the first embodiment are identified with the same reference number, increased by 300. The riser pan  310  is essentially a hybrid of the second and third embodiments described above. Like the riser pan  110  of the second embodiment, the integral combination riser and riser pan  310  of this fourth embodiment preferably has a cylindrical sidewall  316  of a height similar to the height of a regular riser, but also includes a frustro-conical portion  318  to accommodate a secondary cover like the concrete cover  58  shown in FIG. 7.  
         [0080]    Like the riser pan  210  of the third embodiment, the riser pan  310  has at the lower end of the cylindrical sidewall  316  an interrupted annular ring  366 , which is interrupted by a plurality of rib-receiving notches or gaps  368 . An annular wall  372  may be provided axially outwardly of the interrupted annular ring  366 , preferably as an integral extension of the sidewall  316 . An inner sidewall  354  of an inverted channel is also provided axially inwardly of the interrupted annular ring  366 .  
         [0081]    The riser pan  310  further includes a plurality of vertically-oriented ribs  332 , which in this embodiment are located on the interior of the cylindrical sidewall  316  of the riser pan  310 . For purposes of nesting the riser pan  310  with other similar riser pans for shipping or storage, the rib-receiving notches or gaps  368  are sized to accommodate the vertically-oriented ribs  332  of a next-lower riser pan. Likewise, the vertical ribs  270  of a riser  214 , such as on the riser shown in FIG. 17, fit within the rib-receiving gaps  368 . Thus, the interrupted annular ring  366  at the lower end of the wall  316  of the riser pan  310  can lockingly receive either a riser  214  or another riser pan  310 .  
         [0082]    The riser pan  310  also has gussets  348  extending between the exterior of the frustro-conical portion  318  and the inner sidewall  354 . The flat edge  350  at the top of each of the gussets  348  rests along an intermediate, generally flat annular ring  320  running between the frustro-conical portion  318  and the inner sidewall  354 .  
         [0083]    In yet another, i.e. fifth embodiment, shown in FIGS.  22 - 24 , the riser pan  400  may be similar in most respects to the first embodiment described above, but omits the standing circular rib. Instead, the generally flat annular ring  420  extends from the upper end  424  of the frustro-conical pan portion  418 , through the upper cylindrical sidewall  416 , and terminates at an outer edge  428 , outside the upper cylindrical sidewall  416 , thus forming an annular ledge  430  on the exterior of the upper cylindrical sidewall  416 . Contrary to the gusset extensions  52  described above with respect to the first embodiment, the gusset extensions  452  of this embodiment do not terminate along an outer surface of a standing circular rib, because there is no such standing circular rib. Instead, each of the gusset extensions  452  has an angled surface that extends from a flat top  453  of the gusset extension  452  to the generally flat annular ring  420 . In all other respects, the riser pan  410  of this embodiment is substantially identical to the riser pan  10  disclosed in the first embodiment, so further description of the present embodiment is omitted as unnecessarily duplicative.  
         [0084]    In a sixth embodiment of the riser pan  510 , shown in FIGS.  25 - 27 , instead of a standing circular rib  15  extending upwardly from the annular ring  20 , as in the first embodiment of the riser pan  10 , a downwardly-depending circular rib  515  extends from the lowermost end  522  of the frustro-conical pan portion  518 . The downwardly-depending circular rib  515  preferably has two parallel vertical surfaces  517 ,  519 , as opposed to a vertical outer surface  17  and inclined inner surface  19 . However, it is recognized that the inner surface  519  may be inclined, if desired by the manufacturer, to facilitate casting of a cover within the riser pan  510 .  
         [0085]    The riser pan  510  includes gussets  552  and a generally flat annular ring  520  as in the fifth embodiment riser pan  410 , described above, as well as other aspects shown in the drawing figures and described above with respect to previous embodiments, but not described in detail with respect to this embodiment for the sake of avoiding unnecessary repetition.  
         [0086]    Like the standing circular rib  15  shown and described in the first embodiment riser pan  10 , the downwardly-depending circular rib  515  of this sixth embodiment facilitates casting in place of a relatively thicker concrete cover (not shown). Inasmuch as many septic tank lids may have a thickness greater than the height of the frustro-conical pan portion  518 , the circular rib  515  effectively increases the height available in which to cast a concrete cover without the concrete spilling over into the interior region of the riser pan  510  bounded by the upper cylindrical sidewall  516 . The resulting concrete cover would have a two-tiered shape, with a lowermost generally cylindrical portion coinciding with the region of the interior of the riser pan  510  bounded by the downwardly-depending circular rib  515 , and an upper conical portion coinciding with the region of the interior of the riser pan  510  bounded by the frustro-conical pan portion  518 .  
         [0087]    Turning to FIGS.  28 - 30 , a seventh embodiment riser pan  610  utilizes both a standing. circular rib  615   a,  as in the first embodiment, and a downwardly-depending circular rib  615   b,  as in the sixth embodiment. The standing circular rib  615   a  preferably has a vertical outer surface  617   a  and an inclined inner surface  619   a,  similar to the surfaces  17  and  19  in the first embodiment described above. As in the sixth embodiment, the downwardly-depending circular rib  615   b  preferably has parallel outer and inner surfaces  617   b,    619   b,  but it is recognized that the inner surface  619   b  may be inclined, if desired by the manufacturer, to facilitate casting of a cover within the riser pan  610 .  
         [0088]    By providing the standing circular rib  615   a,  the riser pan  610  advantageously assists in preventing the cover, once removed from the riser pan  610 , from being crookedly placed back into the riser pan  610 , like in the first embodiment. As opposed to a two-tiered profile complimenting an inclined pan portion, a step, and an inclined standing circular rib, however, a cover cast into the riser pan  610  would have a profile complimenting not only those portions of the riser pan  610 , but also complimenting the inner surface  619   b  of the downwardly-depending rib  615   b.  An O-ring or annular sealing gasket  661  may also be provided on the step portion  621  intermediate the standing circular rib  615   a  and the pan portion  618  to facilitate a liquid-tight sealing engagement between the riser pan  610  and an internal cover received therein.  
         [0089]    It will be recognized that variations to the foregoing description of the preferred embodiment may be made without departing from the present invention, and which would still be within the scope of the appended claims. For example, the riser pan may have a square or other polygonal shape, rather than round, and the frustro-conical pan portion may have the same or a different shape than the outer wall of the riser pan, as may be desirable for use with stackable risers or other passageways having shapes other than cylindrical.