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FIELD OF THE INVENTION 
     The present invention pertains to apparatus for controlling flushing of a toilet, and more particularly to a device that selectively limits the degree of opening of a water valve such that the amount of water dispensed in a single flush is limited. 
     BACKGROUND OF THE INVENTION 
     Over the years, water conservation requirements have been imposed on residential toilets. Formerly, when no water usage limits were imposed, toilets were built with tanks containing about five gallons. A single flushing apparatus dispensed most of this water. Later, the amount of water stored and dispensed was reduced to about 1.6 gallons per flush. 
     In conventional toilets the water for flushing is held in a tank mounted higher than the toilet bowl and flows from the tank into the bowl when the user opens a valve between the two by depressing a control lever. In some such toilets (usually called flapper toilets) the linkage from the lever to the valve, and the valve itself, are designed so that the valve drops partly or entirely back into its seat, reducing or stopping the flushing, as the user partly or entirely releases the control lever. However, in most conventional toilets, the linkage from the control lever to the valve, and the valve itself, are designed so that as soon as the user depresses the control lever by more than a very minimal amount the valve floats completely off of its seat and the flow of water from the tank into the bowl cannot be reduced or stopped by the user but water flow stops only when the water level in the tank falls almost to the empty level, thereby allowing the valve to sink back to its seat. The present invention pertains to the latter type of toilet. 
     Conserving water in a conventional toilet has been attempted using expedients such as placing bricks in the tank to reduce tank capacity, and bending float rods to lower the water level in the tank. However, none of these prior art efforts have proven entirely satisfactory. 
     Another factor in water conservation is the effectiveness of the flush valve action. Valves may fail to seat properly, thereby continuously leaking tank water into the toilet between flushes. This can account for considerable waste of water over the course of a year. 
     Another attempt at water conservation is using a dual flush lever arrangement, one for relatively great volume flushes and the other for small volume flushes to control the amount of water used. 
     It would therefore be desirable to have an apparatus that adjustably limits the amount of water used in a conventional toilet by giving the user control over the volume and flow rate of water being released for each flush, and promoting effective seating of the valve following the flush. 
     Although water conservation achievable by the toilet user&#39;s having control of the rate and amount of flushing is of prime importance, it is desirable in some circumstances to have the toilet flushing operate without the user&#39;s exercising such control. This may be the case if, for example, the toilet is to be used by a young child, an infirm person, a house guest, or a visitor to a public establishment. It would therefore be desirable to be able to reversibly convert the toilet easily and without expense between the mode in which the user controls the rate and amount of water flow and the mode in which he or she does not. 
     DISCUSSION OF THE RELATED ART 
     U.S. Pat. No. 1,335,763 for CLOSET FLUSH VALVE, issued Apr. 6, 1920 to E. G. Stoltz teaches a spring that exerts downward-directed sealing pressure on a valve. 
     U.S. Pat. No. 1,556,301 for WATER CONTROLLING MECHANISM FOR FLUSH TANKS, issued Oct. 6, 1925 to Daniel A. O&#39;Neill teaches a spring that holds a rod/valve member in a closed position. 
     U.S. Pat. No. 1,932,224 for FLUSH VALVE FOR BOWLS, issued Oct. 24, 1933 to J. A. Mitchell shows a spring that urges a plunger downward against a disk. 
     U.S. Pat. No. 5,440,765 for REVISED AUTOMATIC WATER SHUT OFF FOR STUCK OPEN FLUSH VALVES IN TOILET WATER TANKS, issued Aug. 15, 1995 to Richard L. Weir provides an automatic shut off mechanism for stuck open flush valve. A coil spring, a ball float, and a spring release mechanism separate two cylinders, one within the other. 
     U.S. Pat. No. 5,819,330 for TOILET ENHANCEMENT, issued Oct. 13, 1998 to Don Yokel teaches a flush handle having push button setting for light and heavy flushes. 
     U.S. Pat. No. 7,464,415 for AUTOMATIC CUT-OFF VALVE, issued Dec. 16, 2008 to Ovie L. Randolph teaches a supplemental fill valve for use in a toilet tank. 
     None of the patents, taken singly or in any combination, are seen to teach or suggest the novel toilet flush control device of the present invention. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention a toilet flush control device is provided that limits valve opening and promotes effective closure of the valve. The device limits both the distance and time duration of opening of the valve, so that the amount of water dispensed can be limited. The toilet flush control device also forcibly and effectively returns the valve to its seated or closed position after each flush, thereby assuring effective closure of the valve. The toilet flush control device includes an override feature thereby being readily convertible between a conventional mode of operation and a water-limiting mode of operation. 
     It is, therefore, an object of the invention to provide a novel toilet flush control device, for use in toilet tanks utilizing a rigid rod to connect the flushing handle to the flush valve, the rigid rod typically being held in place by a guide. 
     It is another object of the invention to provide a flush control device that utilizes a compressible spring disposed between the flush valve and the guide. 
     It is yet another object of the invention to provide a flush control device wherein release of the control lever frees the spring to expand, thereby propelling the flush valve back into a seated or closed position. 
     It is also an object of the invention to provide a flush control device wherein the user can open the flush valve fully or, optionally, open the flush valve partially by operating and holding the control lever less than fully. 
     It is a further object of the invention to provide a flush control device wherein when the toilet is flushed, the rising valve compresses the spring thereby limiting upward movement of the flush valve. 
     It is a still further object of the invention to provide a flush control device that provides a user controllable flushing duration wherein release of the flushing lever immediately closes the flush valve. 
     It is yet another object of the invention to provide a flush control device that may readily be overridden by hand (i.e., by manual detachment of enclosing portions of the flush control device from one another) to allow conventional operation of a toilet into which the flush control device is installed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various objects, features, and attendant advantages of the present invention will become more fully appreciated as the same becomes better understood when considered in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the several views, and wherein: 
         FIG. 1  is a side cross sectional view of a toilet flush control device in accordance with the invention; 
         FIG. 2  is a front, elevational view of a flushing mechanism for a toilet with the toilet flush control device of  FIG. 1  incorporated therein; 
         FIG. 3  is a front elevational view of the flushing mechanism for a toilet of  FIG. 2  with the toilet flush control device in an operative, compressed position, and with the toilet flush valve open; and 
         FIG. 4  is a front, elevational view of the flushing mechanism for a toilet of  FIG. 2  with the toilet flush control device in an operative, expanded position with the toilet flush valve closed. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention provides a toilet flush control device for controlling water discharge from a toilet water tank during a flushing operation and also ensuring tight closure of a flush valve upon release of the toilet&#39;s flush handle. 
     Referring first to  FIG. 1 , there is shown a novel toilet flush control device  100  for limiting duration and travel of the flush valve of a toilet, in toilets having a rigid linkage rod leading to and connected to the flush valve. 
     The toilet flush control device  100  has a compressible coil spring  102  having a proximal end  114  and a distal end  116 . Coil spring  102  is contained (i.e., enclosed) within a housing  104  that comprises a hollow cylinder. The housing  104  comprises a sleeve  106  and an end cap  108 . The sleeve  106  and the end cap  108  each have respective openings  110 ,  112 , not shown, for passing the rigid linkage rod entirely through the toilet flush control device  100 . The openings  110 ,  112  are large enough to accommodate the diameter of the linkage rod, and will typically be between approximately one sixteenth and three eights of an inch in diameter. 
     End walls  118 ,  120  serve to retain the coil spring  102  within the housing  104  when the sleeve  106  is connected to the end cap  108 . The sleeve  106  and the end cap  108  may have respective mutually mateable screw threading  122 ,  124  so that the end cap  108  may be removably coupled to the sleeve  106  when it is desired to maintain the coil spring  102  in a compressed configuration. 
     In an uncompressed or free state, coil spring  102  limits travel of the flush valve  142  ( FIG. 4 ) of the toilet. 
     In a compressed configuration, the toilet flush control device  100  is inhibited or overridden. Flush valve  142  may then travel freely. 
     Of course, fastening arrangements for holding the sleeve in the housing are not limited to threading. Rather the inventive concept and enhancement may be applied using various methods for connecting and disconnecting a sleeve within a housing. Such methods are believed to be well known to those of skill in the art and are not further described herein. 
     Referring now also to  FIG. 2 , there is shown a portion of a flushing mechanism contained within the water storage tank  140  of a toilet, tank  140  not shown in its entirety, for operating a flush valve  142 . The linkage includes a manual operator such as a control lever  132  which is accessible from outside the toilet, an arm  134 , and a lift rod that, when raised by arm  134 , lifts a rigid rod  136  that leads to and is connected to the flush valve  142 . The rigid rod  136  is held in vertical orientation by a guide arm  138 . 
     In  FIG. 2 , toilet flush control device  100  is shown with the end cap  108  threaded to the sleeve  106 . The rigid rod  136  has been passed entirely through the toilet flush control device  100 . The housing  104  is selectively disposed to hold the toilet flush control device  100  in a compressed state exerting no significant influence on valve operation, so that the toilet operates in conventional fashion. 
     Referring now also to  FIG. 3 , there is shown the toilet flush control device  100  in its operative condition, with the control lever  132  shown in the flushing position. The purpose of the toilet flush control device  100  when in its operative condition is to limit valve travel when the valve  142  is opening to release water from the water storage tank during a flushing event and to return the flush valve  142  forcibly back to the closed position depicted in  FIG. 4 . In the operative condition, the end cap  108  is uncoupled from the sleeve  106 . End wall  118  of end cap  108  is forced upward against a lower surface, not specifically identified, of guide arm  138  by coil spring  102 . End wall  120  of sleeve  106  is concurrently forced against an upper surface, not specifically identified, of flush valve  142 . Coil spring  102  is still somewhat compressed, although not as much as seen in  FIG. 2 . The coil spring  102  exerts a downward pressure, as seen in  FIG. 3 , on the sleeve  106 . A similar force is exerted on flush valve  142 . 
     Referring now also to  FIG. 4 , there is shown the position of the flush mechanism after the user releases the control lever  132  at the conclusion of the flush operation. Control lever  132  and the arm  134  pivot clockwise, as seen in  FIG. 4  and as indicated by the arrow  148 . Coil spring  102  continues to exert an upward force on end cap  108  and a downward force on the sleeve  106 . End cap  108  is constrained from moving upwardly responsive to the force of the coil spring  102 . However, flush valve  142  is forced downwardly by spring force into the drain conduit, not specifically identified, where it is securely seated. The drain conduit leads to the bowl of the toilet, not shown, so as to discharge released water into the bowl to flush any contents therefrom. 
     It will be recognized that it is possible to form a housing such as the housing  104  in three pieces or sections such as to include a central sleeve and an end cap at each end of the sleeve (this construction is not illustrated) in place of the two-piece construction described herein. It would also be possible to provide the housing in somewhat open form, such as that of a cage. 
     It is also possible to provide the function satisfied by the coil spring  102  by using another form of spring device. Also, the spring device may be located outside the housing, disposed in a manner that does not interfere with manual detachment and/or reattachment of sleeve portion  106  and end cap portion  108  of housing  104 . 
     While the present toilet flush control device has been described in connection with what is considered the most practical and preferred embodiments, it is to be understood that the present invention is not to be limited to the disclosed arrangements, but is intended to cover various arrangements which are included within the spirit and scope of the broadest possible interpretation of the appended claims so as to encompass all modifications and equivalent arrangements that are possible. 
     Since other modifications and changes varied to fit particular operating requirements and environments will be apparent to those skilled in the art, the invention is not considered limited to the example chosen for purposes of disclosure, and covers all changes and modifications which do not constitute departures from the true spirit and scope of this invention. 
     Having thus described the invention, what is desired to be protected by Letters Patent is presented in the subsequently appended claims.

Summary:
A device for controlling valve travel of the flush valve of a toilet operated by a rigid linkage rod and for forcibly returning the valve to the closed position. The device may comprise a spring contained within a sleeve. The sleeve has end caps bearing openings for passing the rigid linkage rod entirely through the sleeve and spring. One end cap may be threaded to enable it to compress and immobilize the spring for selectively defeating operation.