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CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    Not applicable. 
       STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       BACKGROUND OF THE INVENTION 
       [0003]    The present invention relates to plumbing fixtures, and more particularly to the drain at the base of a shower enclosure. 
         [0004]    Bathroom plumbing fixtures such as bath tubs, spas, whirlpools, shower stalls, shower surrounds, free standing partial or full shower enclosures, etc., are well known. Such fixtures can be installed in combination or as separate and discrete fixtures. In the case of stand alone shower enclosures, the upright walls that surround the enclosure are typically mounted onto to a generally flat base, sometimes referred to in the industry as a shower or base “receptor”. U.S. Pat. No. 3,457,568 provides an example of a prior art base receptor. 
         [0005]    In addition to supporting the enclosure walls, the shower base receptor is also the floor of the enclosure on which a person stands during a shower. As such, the floor surface needs to be capable of bearing loads as well as flat and free of uneven surfaces that would be difficult or uncomfortable to stand on. At the same, the base receptor must have a drain to evacuate the water from the shower. 
         [0006]    Many conventional base receptors provide for a recessed drain opening that is only covered by a small grate having openings for the water to pass through. The grate is recessed as well to be generally flush with the floor. However, the openings in the grate must be left unblocked and otherwise make it uncomfortable to stand on with bare feet, and therefore, the usable floor space in the enclosure is effectively reduced by the area of the grate where a person in the shower would avoid standing. 
         [0007]    One approach to overcoming this problem is disclosed in U.S. Pat. No. 5,458,769. This patent describes a floor drain that can be used in a shower environment, albeit not specifically disclosed as for a base receptor, in which the drain opening is covered by a “bell” that can be mounted within the drain opening so that its generally flat, smooth top surface is flush (or near flush) with the surrounding floor. Fluid drains into the drain opening through a narrow passage extending around the periphery of the bell. The bell provides an improved and enlarged stepping area than conventional grates since one can comfortably stand on the smooth top surface of the bell without blocking drain flow through the narrow peripheral passage. 
         [0008]    However, this type of covered drain typically significantly reduces the effective passage area through which water can drain, thereby reducing flow rate and possible causing flow back-up and standing water in the base receptor. Standing in drain water is unpleasant, and the raised water can slip over the short rim of the receptor base. 
         [0009]    The slow drain problem is exacerbated when the water passing through the drain forms a vortex caused by the coriolis effect arising from suction through the drain. The vortex generates a whirlpool-like swirling action in the water as it passes down through the drain. The swirling action of the water passing through the drain can cause water that would otherwise be at the center of the drain to move outwardly toward the drain walls. The unoccupied space in the center of the drain thus effectively diminishes the passage area of the drain, and in further slows the flow rate. 
         [0010]    Anti-vortex drains have been developed to break the vortex and allow water to pass through the full area of the drain. These anti-vortex drains are known in the swimming pool industry, and are used to address problems with debris clogging the drain and/or circulatory pumping system of the pool. They have also be developed to address safety concerns caused by the force of the suction of the circulatory system pulling body parts, particularly that of small children, toward or into the drain. 
         [0011]    U.S. Pat. No. 5,341,523 discloses one prior art anti-vortex drain for a swimming pool application. The disclosed drain breaks up the vortex at the drain by using a large, flat circular cover flush-mounted within the drain opening. Water drains around the circular periphery of the cover in a more steady manner with less swirling action. The disclosed drain provides for adjustment of the opening size of the peripheral passage to allow for slight flow rate adjustment. 
         [0012]    The disclosed drain would be too large and cumbersome for use in a shower receptor. Moreover, like other conventional covered drains, the reduction in drain passage area caused by use of the cover would slow the flow rate through the drain excessively in gravity feed drainage systems, such as shower applications, such that water would likely accumulate around the drain. Thus, the drain disclosed in the &#39;423 patent, even though it is able to reduce or eliminate the vortexes and allow for passage area adjustment, would likely be suitable only for large volume applications, such as pools, which have forced flow circulatory systems and do not need to prevent water from accumulating around the drain. 
         [0013]    Hence, a need exists to provide a shower base receptor with a covered drain system that has enhanced flow characteristics. 
       SUMMARY OF THE INVENTION 
       [0014]    The invention provides a base and drain assembly for a shower enclosure. Specifically, the base has a receptor for mounting at least one upright wall of the shower enclosure. The receptor base also has a floor, a drain well and a drain opening. The drain well is recessed into the floor at the drain opening and defines a drain well perimeter extending about the drain opening. A drain cover is mounted within the drain well above the drain opening in essentially flush relation with adjacent areas of the floor. The drain cover has a drain cover perimeter spaced from the drain well perimeter so as to define a peripheral passage therebetween for peripheral flow to the drain opening beneath the drain cover. The drain cover has one or more anti-vortex ribs extending along an underside of the drain cover and toward the drain opening proximate the drain opening so as to disrupt a vortex in the water passing through the drain opening. 
         [0015]    A preferred radially converging array lays out the ribs in angular spaced apart relation extend in radial directions such that a centerline of each rib intersects a vertical central axis of the drain cover. The ribs can be radially spaced from and symmetric about the central axis, such as in an even number of ribs, for example four, opposed to each other on opposite sides of the central axis. At least one anti-vortex rib extends to a prescribed height above the drain opening, preferably less than 0.25 inches, and more preferably between 0.10 and 0.15 inches, such as 0.13 inches. Further, one or more of the anti-vortex ribs can be contoured to follow a contour of at least one of the drain well and the drain opening. The ribs are preferably formed as a unitary part of the drain cover extending downwardly along the underside thereof. 
         [0016]    The drain cover has an essentially planar upper surface. The drain cover perimeter is defined by at least four sides. One or more of the sides can be straight and/or one or more of the sides can be curved. In any case, the peripheral passage for drain flow can be made to be of an essentially constant dimension about the drain cover. The drain cover can have one or more edge spacers, such as one at each corner, for maintaining the horizontal dimension of the peripheral passage. The drain cover can also have one or more stand offs, again such as one each corner, for contacting the drain well and achieving a vertical gap between the drain well and other portions of the drain cover. Furthermore, the drain cover can be adapted for removable attachment to the base receptor, such as having one or more suction cups for attaching to the surface of the drain well. 
         [0017]    Thus, the shower base receptor and drain assembly of the present invention provides a covered drain system with enhanced flow characteristics, particularly increased flow rate through the drain when compared to an uncovered drain of the same opening dimension. 
         [0018]    Other advantages of the invention will be apparent from the detailed description which follows and accompanying drawings. What follows is merely a description of a preferred embodiment of the present invention. To assess the full scope of the invention the claims should be looked to as the preferred embodiment is not intended to be the only embodiment within the scope of the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  is perspective view of a shower receptor having a flow enhancing covered drain according to the present invention; 
           [0020]      FIG. 2  is a similar perspective view showing the drain cover exploded from the shower receptor; 
           [0021]      FIG. 3  is top plan view of the covered drain as shown in  FIG. 1 ; 
           [0022]      FIG. 4  is a perspective view of the drain cover of  FIG. 1  in isolation; 
           [0023]      FIG. 5  is a top plan view thereof; 
           [0024]      FIG. 6  is a front elevational view thereof; 
           [0025]      FIG. 7  is an end elevational view thereof; 
           [0026]      FIG. 8  is a bottom plan view thereof; 
           [0027]      FIG. 9  is a sectional view of the covered drain taken along line  9 - 9  of  FIG. 3 ; and 
           [0028]      FIG. 10  is a sectional view thereof taken along line  10 - 10  of  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0029]    The accompanying  FIGS. 1-10  illustrate a preferred embodiment of a base and drain assembly  20  according to the present invention for a shower enclosure, referred to generally by numeral  22 . The term “shower enclosure” is used herein to refer to an area where water is sprayed down onto a person that is either standing or sitting. This area can have one or more upright walls  24 , three walls are shown in phantom in  FIG. 1 , and a door or curtain (not shown) so that it is either fully or partially enclosed along one or more sides or the entire boundary of the area. Although not shown, a curtain or a pivotal door could be mounted at the front of the shower enclosure  22  for privacy and to keep water from splashing out of the enclosure. 
         [0030]    The assembly  20  includes a receptor base  26  providing a drain opening  28  and floor  30  of the shower enclosure  22 . The upright walls  24  are supported by the receptor base  24  along the peripheral edges and adjacent the rear and side flanges  32 . The floor  30  is a dished bottom surface that slopes toward the drain opening  28  located in a recessed drain well  34  at its center. The drain well  34  has a generally vertical edge walls  36  defining the drain well periphery  38 . 
         [0031]    The drain well  34  removably receives a drain cover  40  as shown in  FIGS. 1 ,  2 ,  3 ,  9  and  10 . The drain cover  40  mounts inside the drain well  34  so as to be essentially flush with the surrounding areas of the floor  30 . Referring to  FIGS. 4-8 , the drain cover  40  has a smooth, generally flat top surface  42  that terminates at a four-sided peripheral edge having straight, parallel short sides  44  and two convex long sides  46  extending between the short sides  44 . The sides  44  and  46  define the drain cover periphery  50 . The flush mounting and smooth, flat surface at the top of the drain cover  40  make it comfortable to stand on. 
         [0032]    The underside of the drain cover  40  has several elements formed integrally with the top surface  42 . Four receptors  60  are formed at the four corners of the drain cover  40  for support elastomeric stand-offs  62  providing contact surfaces resting against both the recessed floor within the drain well  34  as well as the peripheral edge walls defining the drain well periphery  38 . The stand-offs  62  thus provide firm, yet slightly cushioned contact areas for the drain cover  40  to seat inside the drain well  34  centered within the drain well periphery  38 . Of course, the stand-offs  62  could be formed of the same material as the rest of the drain cover  40 , however, using a co-molding process the elastomeric material can be used to permit flexibility along a controlled range of vertical and lateral movement of the drain cover  40  within the drain well  42  when a load is applied to the drain cover  40 . Six small cylindrical “buttons”  64  with co-molded elastomeric material are also formed at the underside of the drain cover  40  to provide for cushioned structural support against vertical loading. 
         [0033]    For example, under wet conditions, a 70 lb-f load and with the stand-off spaced 0.63 inches from the drain cover periphery, the drain cover  40  could be permitted to move at the short sides  44  laterally (horizontally) 0.011 inches and vertically 0.007 inches, at the long sides 0.04 inches laterally and 0.005 inches vertically, and at the and corners 0.19 inches at the corners, and 0.008 inches vertically. Moreover, it is further noted that each of the stand-offs  62  could be formed in two parts, one for supporting vertical loads and one for centering the drain cover  40  in the drain well  34 . It should be noted that while these values are provide for a 70 lb-f load, the drain cover  40  is preferably rated for 300 lb-f loads, as is commonly required by code for grates. 
         [0034]    Furthermore, the underside of the drain cover  40  has two receptors  66  near the midpoint of the long sides  46  for receiving suction cups  70 . The suction cups  70  removably attach to the floor within the drain well  34  and apply a releasable vertical (and lateral) suction force tending to keep the drain cover  40  mounted within the drain well  34 . 
         [0035]    By centering the drain cover  40  within the drain well  34  and limiting the movement therein, the stand-offs  62  serve to maintain a peripheral passage  78  extending about the drain cover  40  at the spacing between the drain cover periphery  50  and the drain well periphery  38 . In the preferred embodiment described herein, the peripheral passage  78  is of an essentially constant gap width “W” (see  FIG. 3 ), or lateral or horizontal dimension, along its entire length. Aesthetics are enhanced by keeping the gap width as narrow as possible. However, when the gap width is so small that it corresponds to a lower passage area than that of the drain opening  28  the drain cover  40  may become a restriction to drain flow such that flow rate is diminished sufficiently to cause water to accumulate in the receptor base  24 . Other factors will also affect the selection of the gap width. Such factors include the shower flow rate, the number of shower heads, the location and direction of spray and the slope the receptor base floor. However, it has been determined empirically that a gap width dimension of between 0.1 and 0.25 inches is suitable for many common household shower applications with a 2 inch inner diameter drain opening, with a range of 0.13 to 0.16 inches being even more preferable. In the preferred embodiment described herein, a 0.13 inch gap width corresponds to a 5 square inch passage area and a 0.16 gap width corresponds to a 6.2 square inch passage area. 
         [0036]    As best shown in  FIG. 8 , in addition to these elements, the underside of the drain cover  40  includes a number of ribs, including structural ribs  80  and anti-vortex ribs  90 . Two of the structural ribs  80  extend near and parallel to the short sides  44 , intersecting the two buttons  64  nearest the short sides  44 . The other four structural ribs  80  are arranged in a diagonal, radially converging pattern extending from the four buttons  64  toward the center of the drain cover  40  intersected by a vertical center axis  92  thereof (see  FIG. 8 ). 
         [0037]    The four anti-vortex ribs  90  are arranged in a radially converging pattern as well. In the orientation of the drain cover  40  as shown in  FIG. 8 , the anti-vortex ribs  90  at the 12 o&#39;clock and 6 o&#39;clock positions extending radially toward the center axis  92  from the suction cup receptors  66 . The other two anti-vortex ribs  90  are at the 3 o&#39;clock and 9 o&#39;clock positions and extend from the buttons  64  that intersect the structural ribs  80  at the short sides  44  of the drain cover  40 . 
         [0038]    The arrangement and quantity of anti-vortex (and structural) ribs can vary. However, the radial array arrangement allows the ribs to channel water toward the center of the drain opening  28  from all sides of the drain cover  40  along the entire drain cover periphery  50 . While other arrangements could be used, those that act as baffles or others impede flow to the drain opening  28  should be avoided so as not to slow the flow rate. 
         [0039]    The number of anti-vortex ribs in the preferred embodiment described herein was selected to be four after empirical evidence determined an increased flow rate when compared to both no anti-vortex ribs and eight anti-vortex ribs. For example, it was determined that, holding other parameters constant, four ribs provided an 11% improvement in flow rate when compared to eight ribs. 
         [0040]    All of the ribs  80  and  90  depend transversely (vertically) from the underside of the drain cover  40 , and can be parallel to the center axis  92 . The structural ribs  80  are sized to meet the loading requirements of a covered shower drain, for example 300 lb-f. The shape and transverse dimension of the anti-vortex ribs  90  are selected to prevent, eliminate, disrupt or otherwise break up any vortex that would otherwise be present in the drain. 
         [0041]    As can be seen in  FIGS. 6 ,  7 ,  9  and  10 , the bottom edge of the anti-vortex ribs  90  are shaped in part with a curve to follow the contour of the drain well  34  surrounding the drain opening  28 . The remainder of the anti-vortex ribs  90  are configured to extend to a prescribed height “H” above the drain opening  28  when the drain cover  40  is installed in the drain well  34 . Thus, the bottom edge can be straight, that is generally parallel to the top surface  42  of the drain cover  40 , however, the portion show straight could also be oblique to the top surface  42 , curved generally, or otherwise configured to follow a particular contour. 
         [0042]    The prescribed height H, that is the distance from the bottom of the anti-vortex ribs  90  and a top plane of the drain opening  28 , significantly effects the break up of the vortex, and in turn the flow rate through the drain. The prescribed height “H” (see  FIG. 10 ) is selected to meet the flow conditions of particular shower applications. It has been determined empirically that for common shower applications a preferred range of heights H is 0.1 to 0.25 inches, with 0.13 inches being one preferred height which was determined in a four anti-vortex rib arrangement to provide a 3% increase in flow rate when compared to 0.25 inches, all other parameters being the same. 
         [0043]    It was found that the presence of the drain cover  40  using anti-vortex ribs  90  to eliminate the vortex at the drain opening  28  actually increases the flow rate through the drain opening  28  over that when no drain cover  40  was used at all. Empirical study has shown that in a particular gravity fed shower drain application in which a conventional drain grate  100 , as shown in  FIGS. 9 and 10 , was placed over the drain opening  28 , has a maximum flow rate of 14 gpm through the drain opening  28  increased to 17 gpm using a drain cover  40  according to the present invention in which there was a 0.13 inch gap width at the peripheral passage  78  and a 0.13 height between the anti-vortex ribs  90  and the top of the drain opening  28 . 
         [0044]    While there has been shown and described what is at present considered a preferred embodiment of the invention, various changes and modifications can be made therein without departing from the scope of the invention defined by the appended claims. Therefore, various alternatives and revised embodiments are contemplated as being within the scope of the following claims. 
       INDUSTRIAL APPLICABILITY 
       [0045]    The invention provides a base for a shower enclosure having a flat stepping area at a covered drain with peripheral flow and anti-vortex features that enhance the flow rate of water through the drain.

Summary:
A shower enclosure base has a flow enhancing flush-mounted drain cover that conceals the drain opening and provides a flat stepping surface. Drain flow is achieved through a narrow peripheral passage between the drain cover and the drain well in which it is seated. Despite the reduced flow area of passage, flow enhancing features of the drain cover serve to improve the flow rate through the drain. These features are radially converging ribs at the underside of the drain cover that interrupt the natural tendency for drain water to form a vortex as it passes into and through a circular drain opening. The drain cover can be removably secured to the base by suction cups that attach to the drain well.