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FIELD OF THE INVENTION 
     This invention relates to a window or door drain and, more particularly, relates to a water drain or weep hole at the base of an extruded window or door sash or frame. 
     BACKGROUND OF THE INVENTION 
     Frames used for mounting sliding or rolling vent panels in windows or doors are commonly made of extruded plastic or metal alloy members. The window frame is formed with channels having vertical walls or flanges to accommodate and mount both the sliding or rolling panel and the fixed panel. Such construction is susceptible to moisture ingress, resulting in the collection of water in the channels of the sash. To drain the collected water, weep holes are provided in the flanges or the walls of the channels in the sash. 
     During storms, winds of high velocity cause a zone of high air pressure on and adjacent the walls of buildings, relative to the air pressure within the buildings and relative to the air pressure within the sashes of windows located on said walls, particularly if said windows are snugly mounted. The interiors of the window frames, such as extruded plastic or metal window frames, are essentially hollow and contain recesses in which single, double and triple-glazed window panes are mounted by means of continuous resilient flanges. The high exterior air pressure thus in effect generates a partial vacuum within the window frames which sucks up water as it flows down and across the exterior faces of the windows during storms to accumulate within the window frames. 
     U.S. Pat. No. 3,314,201 discloses a construction comprising inner and outer channels, characterized by an inside and outside flange, and a common flange between the two channels. A weep hole is provided in the common flange to drain the inner channel into the outer channel and then out through a weep hole provided in the outside flange. The weep hole in the common flange includes a flapper valve for preventing inward flow of dirt or moisture into the inner channel. Unfortunately, where a partial vacuum is generated in the window, as above described, the flapper valve may close, preventing escape of collected liquid in the inner channel. 
     SUMMARY OF THE INVENTION 
     In one broad aspect the present invention provides a window unit including an extruded frame and a moveable window panel, the frame comprising a channel for mounting the window panel therein, a cavity disposed outwardly of the channel, first and second throughbores for facilitating communication between the channel and the cavity, wherein the first throughbore is disposed at a level below the second throughbore, a third throughbore for facilitating communication between the cavity and an external environment, and a first weeper, mounted in the first throughbore, including a flapper valve characterized by open and closed positions, wherein the flapper valve assumes the open position upon urging by fluid pressure in the channel. The window unit can further include a second weeper, mounted in the third throughbore, including a flapper valve characterized by open and closed positions, wherein the flapper valves assumes the open position open urging by fluid pressure in the cavity. 
     In another aspect the present invention provides a water drain unit for insertion in a mating wall slot in a window unit, comprising a frame, a first and a second set of mating holes formed in the frame, a first seating surface including a first orifice, and a second seating surface including a second orifice, wherein the first and second seating surfaces are mounted in the frame and wherein the first and second orifices are in communication, and a flapper valve mounted within either of the first or second set of mating holes for seating against the first seating surface when mounted in the first set of mating holes and for seating against the second seating surface when mounted in the second set of mating holes. The frame can further comprise a peripheral flange disposed at a first end for abutment against the wall of a window unit, and defining a drain opening, a deep upper wall with a plurality of upstanding ribs extending therefrom for frictional engagement with the wall slot, a shallow lower wall with a plurality of pliable ribs depending therefrom for frictional engagement with the wall slot, and first and second sidewalls extending between and joining the upper and lower walls, each of the sidewalls terminating and merging with a second end of the frame to define a second open end. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The weep hole construction of the invention will now be described in detail with reference to the accompanying drawings, in which: 
     FIG. 1 is a partially cut-away front perspective view of a window unit of the invention; 
     FIG. 2 is a similar to FIG. 1 with the window being removed from the window frame; 
     FIG. 3 is a front perspective view of an external weeper of the invention; 
     FIG. 4 is a perspective view of the weeper in FIG. 3 showing the weeper in a closed position; 
     FIG. 5 is a side elevation view of the weeper in FIG. 3 showing the weeper in a closed position; 
     FIG. 6 is a front perspective view of the weeper in FIG. 3 showing the weeper in an open position; 
     FIG. 7 is a side elevation view of the weeper in FIG. 3 showing the weeper in an open position; 
     FIG. 8 is a perspective view of an internal weeper of the invention; 
     FIG. 9 is a side elevation view of the weeper in FIG. 8 showing the weeper in a closed position; 
     FIG. 10 is a perspective view of a weeper in FIG. 8 showing the weeper in a closed position; 
     FIG. 11 is a side elevation view of a weeper in FIG. 8 showing the weeper in an open position; 
     FIG. 12 is a perspective view of the weeper in FIG. 8 showing the weeper in an open position. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows internal and external weepers or drain units  8  and  10  installed in a frame  12  of a window unit  14 . Frame  12  is formed by extrusion or other conventional means known in the art. The frame  12  is designed for mounting of inner  4  and outer panels  6 , each of such panels comprising one or more glass panes mounted in a sash. In one embodiment, the inner panel is a sliding panel and the second panel is a fixed panel. Frame  12  is provided with a pair of sill flanges  16  and  18  for mounting of the inner panel by snap-fit engagement with stepped contours provided in the sash  5  of the inner panel  4 . Flanges  16  and  18  extend from sidewalls  20  and  22  respectively and are joined by floor  23  to form a first channel  24  disposed and extending peripherally about the perimeter of the first panel. Sash  12  is further provided with sill flanges  26  and  28  for mounting of the outer panel  6  by snap-fit engagement with stepped contours provided in the sash  7  of the outer panel  6 . Flanges  26  and  28  extend from sidewalls  30  and  32  respectively and are joined by floor  33  to form a second channel  34  disposed and extending peripherally about the perimeter of second panel. 
     Referring to FIG. 2, a cavity  36  is also formed within frame  12  during the manufacturing process. Cavity  36  shares sidewall  22  with first channel  24 , which functions as an inner sidewall, and further includes outer sidewall  38 . In this respect, cavity  36  is disposed outwardly of first channel  24 . Upper and lower ends of sidewalls  22  and  38  are joined by a horizontally extending member  40  and downwardly sloping floor  42 . In one embodiment, and as illustrated in FIG. 1, horizontally extending member  40  of third channel  36  is also floor  33  of second channel  34 . 
     First channel  24  includes upper and lower horizontally extending sections  52  and  54  joined by first and second vertically extending sections  56  and  58  (only one is shown). In this respect, first channel  24  extends about the perimeter of the inner panel. Cavity  36  also includes upper and lower horizontally extending sections  44  and  46  joined by first and second vertically extending section  48  and  50  (only one is shown). In this respect, sections  44 ,  46 ,  48 , and  50  of cavity  36  are separated from sections  52 ,  54 ,  56 , and  58  of first channel  24  by sidewall  22  which includes upper and lower horizontally extending sections  22   a  and  22   b  joined by first and second vertically extending sections  22   c  and  22   d  (only one is shown). 
     A throughbore  60  is formed within sidewall section  22   b  to facilitate direct communication and connection between lower section  46  of cavity  36  and lower section  54  of first channel  24 . Throughbore  60  is provided to facilitate drainage of collected moisture in first channel  24  into cavity  36 . Internal weeper  8  is installed in throughbore  60  to control such drainage and, in this respect, includes a flapper valve  62 . Flapper valve  62  is characterized by open and closed positions. Flapper valve  62  is urged into the open position by fluid pressure in first channel  24 . Without such fluid pressure, flapper valve  62  remains closed to seal cavity  36  from first channel  24 . Throughbore  64  is formed in sidewall  38  to facilitate drainage of moisture collected in cavity  36  into the exterior or outside environment. External weeper  10  is installed in throughbore  64  to control such drainage and, in this respect, includes a flapper valve  66 . Flapper valve  66  is characterized by open and closed positions. Flapper valve  66  is urged into the open and closed position by fluid pressure in cavity  36 . Without such fluid pressure, flapper valve  66  remains closed to seal cavity  36  from the external environment. Second channel  34  is formed with its own throughbore and installed with a separate weeper (not shown) to facilitate controlled drainage of second channel  34  directly into the environment. 
     First channel  24  also communicates with cavity  36  via slot or throughbore  69  formed in sidewall  22   a . Throughbore  69  is disposed at a level above throughbore  60 . In one embodiment throughbore  69  is formed with upper sidewall section  22   a . Throughbore  69  effects permanent communication between first channel  24  and cavity  36 . As such, pressure is substantially equalized between first channel  24  and cavity  36 . 
     During high wind conditions, particularly during storms, it is possible that outside air pressure, external to window unit  14 , is higher than the internal air pressure due to conversion of wind velocity head to static pressure. Under these conditions, a relative vacuum is created within the frame whereby water could be sucked into first channel  24 . Simultaneously, the created relative vacuum could also pull the internal and external weepers  8  and  10  into a closed position, thereby preventing escape of collected moisture from within channel  24  and cavity  36 . By providing upper throughbore  69 , pressure within cavity  36  is substantially equalized with the internal air pressure in channel  24 . Because of this, the head of water collected in channel  24  is able to push open flapper valve  62  and allow the water to drain into cavity  36 . Water, therefore, collects in cavity  36  and the head of water eventually forces open flapper valve  66  when sufficient elevation head is developed in cavity  36  to overcome outside air pressure or when the wind velocity and resulting velocity head decreases thereby urging flapper valve  66  into a closed position. 
     With reference now to FIGS. 3 through 13, in one embodiment, drain unit  100  can be provided to serve as either the internal weeper  8  or external weeper  10  of a window unit  14 . Referring to FIGS. 3 to  12 , drain unit  100  has a first end  102  and a second end  104 . Flange  118  is provided at first end  102  including a first drain opening  118   a . First end  102  is joined to second end  104  by, and is formed integral with, rectangular frame  120 . Frame  120  includes an upper wall  122 , a lower wall  126 , and opposing side walls  128  and  130 . Upper and lower walls  122  and  126  extend between and join sidewalls  128  and  130 . Upper wall  122  of frame  120  has a plurality of longitudinal, equispaced, upstanding V-shaped ribs  124  at each end and lower wall  126  preferably has a plurality of longitudinal pliable ribs  132  projecting rearwardly from convex rear edges  134  and  135  of sidewalls  128  and  130 . Each of sidewalls  128  and  130  terminate at respective distal ends  129  and  131  to merge with and define an open second end  104 . The distal ends  129  and  131  bevelled rearwardly upwardly at about 45° from lower edges  134  and  135  to merge with upper wall  122 . Frame  120  also extends into flange  118  along each of the upper and lower walls  122  and  126  and side walls  128  and  130 . 
     Frame  120  includes a first seating surface  138  and a second seating surface  140 . First seating surface  138  extends between upper and lower walls  122  and  126 , and sidewalls  128  and  130 , and further lies in a plane substantially perpendicular to the longitudinal axes of the upper and lower walls  122  and  126 . First seating surface  138  is further disposed rearwardly of flange  118  and is recessed within opening  118   a . First seating surface  138  includes a plurality of substantially equispaced ribs  142  extending between upper and lower walls  122  and  126  with gaps orifices  143  therebetween. Equispaced ribs  142  include terminal ribs  144  extending from each of sidewalls  128  and  130 . Together, ribs  142  and  144  and upper and lower walls  122  and  126  define first seating surface  138  for providing a planar open seat for flapper valve  6 . 
     Second seating surface  140  also extends between upper and lower walls  122  and  126  and sidewalls  128  and  130 , and further lies in a plane substantially perpendicular to the longitudinal axis of upper and lower walls  122  and  126 . Second seating face  140  is interposed between first seating surface  138  and second end  104  and is, therefore, recessed into frame  120  relative to second end  102 . In greater detail, seating surface includes a plurality of substantially equispaced ribs  148  extending between upper and lower walls  122  and  126  with gaps or orifices  149  therebetween. Equispaced ribs  148  include terminal ribs  150  extending from each of sidewalls  128  and  130 . Together, ribs  148  and  150  and upper and lower walls  122  and  126 , define second seating surface  140  for providing a planar open seat for flapper value  62 . 
     First end  102  communicates with second end  104  to provide a flowpath through drain unit  100 . In this respect, opening  18   a  opens into second end via communication with gaps  143  and  149 . 
     Drain  100  can be provided to serve either as external weep  10 , to facilitate escape of moisture collected in cavity  36  or can be provided to serve as internal weep  8 , to drain first channel  124 . 
     Referring to FIGS. 3 to  12 , rectangular flapper valves  62  or  66  are pivotally mounted in frame  120  between first and second ends  102  and  104 . In this respect, cylindrical lug extensions  154  and  156  are provided projecting laterally from respective rounded upper edges of each of flapper valves  62  or  66 . Lug extensions  154  and  156  project into and can be received by respective round mating holes  162 ,  164  and  166 ,  168  formed in the opposed sidewalls  128  and  130 . 
     In one embodiment, either of rectangular flapper valves  62  and  66  is mounted to lie in a plane characterized by an angular position of 4° from the vertical plane or, in other words, a plane which is substantially normal to the longitudinal axis of opening  118   a . This feature improves sealing of flapper valves  62  or  66  against its associated seating surface. Further, less water pressure is required to effect opening of flapper valves  62  or  66 . 
     Each of flapper valve  62  and  66  is slightly shorter in width than the width of respective seating surfaces  138  and  140  in frame  120  and is centered therein by small guide protrusion at each side edge thereof to ensure free pivotal movement of flapper valve  62  and  66 . 
     Upper and lower stiffening flanges  174  and  176  are provided at the bottom front face of each of flapper valves  62  and  66 . Lower stiffening flange  176  has a central protrusion  178  forming part thereof or adjacent thereto adapted to abut against the upper edge of openings to limit the upward movement of respective flapper valves  62  or  66 . 
     Installation of drain unit  100  in throughbore  60  to act as internal weeper  8  will be explained with reference to FIGS. 1,  2  and  8  to  12 . Flange  118  is pressed against internal surface  23  of sidewall section  22   b  to seal drain unit  100  against sidewall section  22   b . Upper ribs  124  ensure a frictional locking engagement with the throughbore  60 , the upper edge  61   a  of through  60  preferably fitting between upper wall  122  and foremost of the ribs  124 . Lower pliable ribs  132  are biased against the lower edge  61   b  of throughbore  60  to provide a water deflector and a seal while urging the frame  120  upwardly against upper edge  61   a  for secure engagement therewith. Flapper valve  62  is installed within mating holes  166  and  168  to facilitate drainage of first channel  24  into cavity  36 , thereby functioning as a one-way check valve. 
     Installation of drain unit  100  in throughbore  64  to act as external weeper  10  will be explained with reference to FIGS. 1 to  7 . Flange  118  is pressed against outer surface of outer sidewall  38  to seal drain unit  100  against sidewall  38 . Upper ribs  124  ensure a friction locking engagement with througbore  64 , the upper edge  65   a  of throughbore  64  preferably fitting between upper wall  122  and foremost of the ribs  124 . Lower pliable ribs  132  are biased against the lower edge  65   b  of throughbore  64  to provide a water deflector and a seal while urging frame  120  upwardly against upper edge  65   a  for secure engagement therewith. Flapper valve  66  is installed within mating holes  162  and  164  to facilitate drainage of cavity  36  into the outside environment, thereby functioning as a one-way check valve. 
     It will be understood, of course that modifications can be made in the embodiment of the invention illustrated and described herein without departing from the scope and purview of the invention as defined by the appended claims.

Summary:
A window unit ( 14 ) has an extruded frame ( 12 ) and a moveable window panel ( 4 ). The frame ( 12 ) has a channel ( 24 ) for mounting the window panel therein and a cavity ( 36 ) disposed outwardly of the channel ( 24 ). The frame ( 12 ) further has first and second throughbores ( 60, 69 ) for facilitating communication between the channel and the cavity, wherein the first throughbore ( 60 ) is disposed at a level below the second throughbore ( 69 ). A third throughbore ( 64 ) is provided for facilitating communication between the cavity ( 36 ) and an external environment. A first weeper ( 8 ) is mounted in the first throughbore ( 60 ), including a flapper valve ( 62 ) characterized by open and closed positions, wherein the flapper valve ( 62 ) assumes the open position upon urging by fluid pressure in the channel ( 24 ). The frame ( 12 ) may also include a second weeper ( 10 ) mounted in the third throughbore ( 64 ) wherein the first and second weepers ( 8, 10 ) can be configured to be an internal weeper ( 8 ) or an external weeper ( 10 ).