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You are an expert at summarizing long articles. Proceed to summarize the following text: 
FIELD OF INVENTION 
     This invention relates to plumbing devices and is particularly directed to improved means for blocking floor sink drain openings to prevent passage of large objects, while allowing free flow of fluid therethrough. 
     As is well known, food preparation kitchens are usually provided with a floor sink having a drain opening which connects to a grease trap or sewer to allow disposal of indirect waste water and the like. Unfortunately, rags, napkins, silverware and other large objects are often washed into the floor sink along with the floor washing water and these objects often get carried into the drain and cause blockage, flooding and other problems. Moreover, the loss of napkins, silverware and the like add significant expense to the operation of the restaurant. Unfortunately, most floor sinks have open drains which are subject to the problems noted above. Some prior art drain grates or screens have been provided which are permanently installed in the drain opening. However, these often become clogged and simply add to the flooding problem. Thus, none of the prior art sink drain screens have been entirely satisfactory. 
     SUMMARY OF THE INVENTION 
     These disadvantages of the prior art are overcome with the present invention and an improved floor sink drain screen is provided which positively precludes passage of large objects, while permitting free passage of fluid and which can quickly and easily be removed for cleaning, when desired. In some embodiments, a special, tamperproof locking key may be used to prevent unauthorized disassembly of the installed floor drain screen. 
     These advantages of the present invention are preferably attained by providing an improved floor sink drain screen lock having expandable means for engaging the walls of a floor sink drain, yet being readily collapsible for quick and easy removal when desired. 
     Accordingly, it is an object of the present invention to provide an improved floor sink drain screen locking apparatus. 
     Another object of the present invention is to provide an improved floor sink drain screen lock which positively precludes passage of large objects. 
     A further object of the present invention is to provide an improved floor sink drain screen lock which positively precludes passage of large objects while permitting free passage of liquids. 
     An additional object of the present invention is to provide an improved floor sink drain screen lock which positively precludes passage of large objects while permitting free passage of liquids and which can quickly and easily be removed for cleaning, when desired. 
     Yet another object of the present invention is to provide improved floor sink drain screen locks having expandable means for sealingly engaging the walls of a floor sink drain, yet being readily collapsible for quick and easy removal when desired. 
     These and other objects and features of the present invention will be apparent from the following detailed description, taken with reference to the figures of the accompanying drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an upper isometric view of a removable locking floor sink drain screen for enlarged opening embodying the invention. 
         FIG. 2  is a lower isometric view of an embodiment of the invention. 
         FIG. 3  is an exploded front view of an embodiment of the invention. 
         FIG. 4   a  is a plan view of an embodiment of the center section of the locking floor sink drain screen. 
         FIG. 4   b  is a plan view of another embodiment of the center section of the locking floor sink drain screen. 
         FIG. 5  is a plan view of the lower section of the locking floor sink drain screen. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  depicts a locking floor sink drain for an enlarged opening, indicated generally at  10 . An upper grate  12  formed with a central opening  14  is surrounded by a plurality of additional openings  16  through which water or any other liquid can be drained. A middle section  18  has a non-expandable section  19  with an internal flange  32  that supports a plurality of vertical separators  22 . An expandable ring section consists of a number of panels  20  separated by a plurality of slits  21  that permit the panels  20  to be forcefully expanded against the inner surface of a drain pipe (not shown). The vertical separators  22  space the grate  12  from the flange  32  and are themselves spaced apart to permit draining liquid to flow into and through the center cavity of the device and down the drain pipe. Positioners  30  attached to the vertical separators  22  interface with the grate  12  to prevent substantial rotational or sliding movement between the grate  12  and the separators  22 . The separators  22  also position and secure the grate  12  above the middle section  18 . 
     A hollow tapered section  24  has an outer diameter  36  that is larger than the inner diameter of middle section  18  and incorporates internal structure to form a threaded hole  28 . Threaded hole  28  receives a threaded bolt  26  that extends through the central opening  14  of the grate  12 , through the middle section  18 , and secures the grate  12  to tapered section  24 . When tightened, the threaded bolt  26  pulls the tapered section  24  upward and into the middle section  18 , causing the panels  20  of the middle section to expand against the inner diameter of the drain pipe. 
     Although depicted as a square plate, the metal grate can be circular, rectangular, or of an irregular shape, depending upon the configuration of the installation environment. 
       FIG. 2  is a lower isometric view of the drain locking device for an enlarged drain. This view provides some detail of the tapered section  24 , and shows exemplary structure through which threaded hole  28  is formed. 
       FIG. 3  shows an exploded front view of the locking device of this invention. Threaded bolt  26  may have a head  40  which may be a slotted screw, a hexagonal head, a tamperproof head, or any other suitable means know in the art for tightening or loosening bolt  26 . In a preferred embodiment, grate  23  may be metallic, such as brass or stainless steel, although any suitable corrosion-resistant material of sufficient strength and flexibility will suffice, and will have an indented portion  38  to receive the head  40  of bolt  26  and position it flush with the upper grate surface. The grate  23  is supported by vertical separators  22 , and optionally may be secured by positioners  30  or, in some embodiments, suitable fastening means to hold middle section  18  in a fixed relationship with respect to grate  23 . Vertical separators  22  are supported by an internal flange  32  located within upper non-expandable portion  19  of middle section  18 . The lower portion of middle section  18  is a plurality of panels  20  being separated by slits  21  whereby the panels  20  may be forced apart and outwardly against the interior surface of a drain pipe (not shown). 
     A frusto-conical tapered section  24  of the device has a threaded through hole  28  that receives threaded bolt  26 . The upper diameter  34  of the tapered section  24  is smaller than the inner diameter of middle section  18 , while the lower diameter  36  of the tapered section is larger than the inner diameter of middle section  18 . As threaded bolt  26  is tightened, tapered section  24  is drawn up against the expandable section  20  of middle section  18 , causing the panels  20  to expand and press against the inner surface of a drain pipe and lock the device into the drain. 
       FIG. 4   a  is a plan view of the middle section  18  of the device of this invention. As viewed from above in  FIG. 4   a , vertical separators  22  may have a rectangular cross-section and a positioning knob or fastening means  30  to interface with the grate  12 . Fastening means  30  may assist in maintaining the physical relationship between grate  12  and middle section  18 , and may be positioning knobs, threaded screws, or any other suitable fastening means known in the art. An internal flange  32  supports vertical separators  22  within non-expandable portion  19  of middle section  18 .  FIG. 4   b  depicts the separators  22  as being curved, and permits flange  32  to have a smaller lip, thus increasing the size of the cavity through which liquid may flow. Although the embodiment depicted in  FIGS. 4   a  and  4   b  shows four separators, the choice of configuration of separators  22  as rectangular or of some other shape, and of the number of separators, is not critical to the function of the invention and may be a matter of design choice. 
       FIG. 5  is a plan view of the tapered section  24 . Threaded through hole  28  receives the threaded bolt  26 , while the smaller upper diameter  34  and larger lower diameter  36  form a frusto-conical surface that will cause expandable panels  20  to be forced outwardly when the tapered section  24  is drawn upward as bolt  26  is tightened. 
     In use, the locking floor sink drain screen  10  is inserted into the mouth of a floor sink drain so that the grate  12  rests on the surface of the area being drained and, preferably, within an indented cavity that will support the grate flush with the surface to be drained. The middle portion  18  and tapered portion  24  of the device are attached to the grate with threaded bolt  26 , and extend downwardly to fit within the upper end of a drain pipe. The bolt  26  is then tightened which serves to draw the tapered section  24  toward the middle section  18 , which causes the expandable panels  20  to expand laterally to wedge against and frictionally engage the drain pipe opening. This ensures that the device  10  will not be displaced during use. Because the device of this invention is intended for use in drains where the drain pipe is smaller than the mouth of the floor sink drain, liquid can flow through openings  16  in the grate  12  and through spaces between vertical separators  22 , and further through the large opening in tapered section  24 , where it will be channeled into the drain pipe. However, any large objects will be blocked by the mesh-like structure of the grate  12 . If the openings  16  become clogged over time, bolt  26  can be loosened, allowing tapered section  24  to be forced downward, releasing friction on expandable panels  20  and allowing the floor sink drain  10  to be removed for cleaning. Subsequently, the drain screen lock  10  can be reinserted in the floor sink drain opening in the manner described above for further use. 
     Bolt  26  may be tamperproof such that special tools are required for installation or removal of the device from a drain. Because the drain pipe will be some distance below the grate and floor openings, the middle section  18  and tapered section  24  may be of any length, and will be sized to fit within a drain of corresponding size. Vertical separators may be of any height but, preferably, will be no longer than about one inch (2.54 cm). 
     Numerous variations and modifications can be made without departing from the spirit of the present invention. Therefore, it should be clearly understood that the forms of the present invention described above and shown in the accompanying drawing are illustrative only and are not intended to limit the scope of the present invention.

Summary:
An improved locking floor sink drain screen for an enlarged drain is provided. The locking floor sink drain positively precludes passage of large objects, while permitting free passage of fluid and which can quickly and easily be removed for cleaning. Vertical separators provide spaces through which water can flow from the enlarged drain opening into a standard drain pipe. In some embodiments, a special, tamperproof locking key may be used to prevent unauthorized disassembly of the installed floor drain screen.