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CROSS-REFERENCE TO RELATED PATENT APPLICATIONS 
     This patent application claims the benefit of U.S. Provisional Patent Application No. 61/102,674, filed Oct. 3, 2008. 
    
    
     FIELD OF THE INVENTION 
     This invention generally pertains to vacuum waste systems and, more particularly, to flush valves for vacuum waste receptacles such as vacuum toilets. 
     BACKGROUND 
     Vacuum waste systems are generally known in the art for use in transportation vehicles such as aircraft. Vacuum waste systems typically comprise a toilet bowl connected by vacuum piping to a waste tank. A flush valve is disposed between the toilet and the vacuum piping. When the flush valve opens, the contents of the toilet bowl are removed by differential pressure to the waste tank because the air pressure in the line under vacuum is lower than ambient air pressure in a toilet bowl. The flush valve maintains the pressure boundary between ambient air in the toilet bowl and the lower pressure of the piping and the waste tank. In an aircraft, the piping may be placed under vacuum pressure at altitudes under about 16,000 feet by a vacuum source. At altitudes about 16,000 feet and above, the vacuum pressure in the piping may be supplied by the atmospheric pressure differential between the cabin and the exterior of the airplane. 
     Conventional flush valves and methods for controlling the removal of waste from the toilet bowl to a waste tank are generally known. Such prior flush valves may use a large, rotating disk having an aperture to admit waste past the aperture. The use of such a large disk is undesirable because it makes the overall flush valve large, heavy and unwieldy for use in confined places such as aircraft lavatories. 
     Furthermore, the use of a disk having an aperture requires precise positioning of the aperture over the waste inlet so that waste moving from the toilet bowl to the piping leading to the waste tank does not catch or accumulate on the perimeter of the aperture or on the solid portion of the disk causing the disk to stick or not seal properly. Also, over time and due to normal wear, the accuracy of the positioning of such disk apertures tend to slip, aggravating the aforementioned problems. 
     Another problem with conventional flush valves using a disk with an aperture to admit waste past the disk is that users are not able to open them manually. This can result in unsanitary back-up of waste in the toilet bowl and overflow of waste from the toilet bowl into the lavatory area if the flush valve becomes stuck in the closed position. 
     A need exists for a smaller, easily installed and more efficient flush valve, which does not rely on a disk having an aperture, for controlling the removal of waste from toilet bowls in a vacuum toilet systems. 
     SUMMARY 
     This invention is generally directed to providing improved power usage, efficiency and reliability in evacuation of waste from a toilet bowl in a vacuum waste system and for providing a more streamlined and compact flush valve design that takes up less space than prior flush valves used in the confined area of aircraft lavatory compartments. The apparatus and method of the invention achieve this by way of a flush valve utilizing a uniquely shaped discharge disk. Such discharge disk does not include an aperture and is just large enough to seal the flush valve outlet. The discharge disk is smaller and lighter than any discharge disk used in prior flush valves. Because the disk is smaller and uniquely shaped, the operation of the disk requires little space and has a relatively small current draw as compared to conventional flush valves. Furthermore, in a preferred embodiment the flush valve is an integral component of a unique lightweight latticed toilet stand. This unconventional integrated design further minimizes the weight and space requirements for the valve. These are important advantages because minimization of weight, space and power usage are top design considerations in the aircraft industry. 
     Additionally, the present valve includes a manual override function for increased reliability. In yet another aspect, the vacuum source used is a centrifugal, single impeller, vacuum generator powered by a brushless DC motor. Because this vacuum generator design generates less heat than prior vacuum generator designs, the impeller and housings of the generator can be made of engineered polymer thereby drastically reducing the generator weight over conventional vacuum generator assemblies used with aircraft flush valves. Also, the smaller and lighter impeller is mounted directly on the motor shaft thereby decreasing the moment of inertia and allowing the vacuum generator to reach and maintain target vacuum pressure while using less power than conventional vacuum generators. These and other advantages of the invention will be apparent from the description of the invention provided herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-noted and other advantages of the invention will be apparent from the description of the invention provided herein with reference to the attached drawings in which: 
         FIG. 1  is a perspective view of the outside of the back of one side of a latticed toilet stand showing key components of the flush valve of the present invention as an integral part of the toilet stand side; 
         FIG. 2  is a perspective view of the front of the toilet stand side depicted in  FIG. 1  in which a cover is applied to enclose the flush valve components; 
         FIG. 3  is a perspective view of the cover of the flush valve in accord with an embodiment of the present invention; 
         FIG. 4  is a cross-section view of  FIG. 1 , taken along lines  4 - 4  of  FIG. 1 ; 
         FIG. 5  is a perspective view of the discharge disk in the flush valve in accordance with an embodiment of the present invention; 
         FIG. 6  is a perspective view of the disk of  FIG. 5  as compared to the size and shape of flush valve disks of the prior art; 
         FIG. 7  is a perspective view of the vacuum generator in accordance with the present invention; 
         FIG. 8  is a perspective view of the vacuum generator in accordance with the present invention; 
         FIG. 9  is a cross sectional view of the vacuum generator of  FIG. 8  taken along lines  9 - 9 ; and 
         FIG. 10  is a perspective view of the toilet stand showing the side panel incorporating the flush valve. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The embodiment of the invention described below is not intended to be exhaustive or to limit the invention to the precise structure and operation disclosed. Rather, the embodiment described in detail below has been chosen and described to explain the principles of the invention and its application, operation and use in order to best enable others skilled in the art to follow its teachings. 
     This invention is generally directed to a flush valve and method for controlling the evacuation of waste from a toilet in a vacuum waste system, including particularly an aircraft vacuum waste system. The following examples further illustrate the invention but, should not be construed as in any way limiting its scope. 
     Turning now to  FIGS. 1-4 , an embodiment of the flush valve of the present invention for controlling the evacuation of waste from a toilet in a vacuum waste system is labeled  10 . In this embodiment of the invention, flush valve  10  is designed as an integral component of a toilet supporting stand  40  ( FIG. 10 ) for a vacuum toilet waste receptacle  47 . The toilet supporting stand  40  has four interlocking sides,  41 ,  42 ,  43  and  44  each of which has an open lattice structure, as shown, to minimize weight and maximize structural strength. Stand  40  is described in detail in a U.S. patent application entitled “Vacuum Waste System and Method for Using the Same,” Ser. No. 61/102,812, filed Oct. 3, 2008. The disclosure of this contemporaneously filed application relating to the structure of the stand is incorporated by reference. 
     Sides  42  and  44  have a series of interlocking dovetails  28  ( FIGS. 1-2  and  10 ) on their edges for attachment to the dovetail receivers  48  ( FIG. 10 ) of adjacent panels  41  and  43  of the stand. In other embodiments, Sides  42  and  44  may have a series of dovetail receivers on their edges for attachment to dovetails of adjacent panels  41  and  43  of the stand. Stand side  44  shown in  FIGS. 1-2  depicts the flush valve  10  of the invention as a component of side  44  of the stand. The key components of the valve comprise a discharge disk  16 , a driver gear  18 , a follower gear  20 , an actuator shaft  22  ( FIG. 4 ), a follower shaft  24 , and a sensor  25  ( FIG. 4 ), all of which are mounted to stand side  44  as shown. A front valve cover  14  is attached to the stand panel  44  by threaded fasteners  45  or other appropriate means in order to at least partially enclose the discharge disk  16  which is located in a cavity between side panel  44  and the cover  14 . Gasketing (not shown) is interposed between side panel  44  and cover  14  to create a seal to prevent leakage from the cavity. 
     Stand side  44  includes an integral annular flange  30  positioned above the discharge disk with an outlet port  31  (as best seen in  FIG. 4 ) aligned with a corresponding inlet port  27  in the front valve cover  14 . The cover  14  includes an annular flange  26  that has an inlet port  27  which receives waste from the toilet bowl (not shown). The outlet port  31  is attached to piping (not shown) and is in fluid communication with the inlet port  27  and a waste tank (not shown) when the discharge disk  16  is open (as discussed subsequently). 
     An appropriate conventional flush valve actuator  46  (as shown diagrammatically in  FIG. 4 ) has an integral actuator shaft  22 . In a preferred embodiment the flush valve actuator is a 28 VDC motor. The actuator shaft  22  is attached to and rotates driver gear  18  when the flush valve actuator is operated. The driver gear has an integral extension arm  32  for manually opening and closing the flush valve. As best seen in  FIGS. 1 and 4 , a follower gear  20  meshes with the driver gear  18  and turns a follower shaft  24  attached to a discharge disk  16  ( FIG. 4 ). 
     Discharge disk  16  is disposed between the inlet port  27  and the outlet port  31 . The discharge disk  16  includes a rotary section  23  and a covering section  29 . The rotary section  23  of the discharge disk  16  is the portion of the discharge disk  16  that is attached to the follower shaft  24 . The covering section  29  is the portion of the discharge disk  16  that is of a size and shape corresponding to the size and shape of the outlet port  31 . The covering section  29  is continuous insofar as it does not include any apertures or holes. The rotary section  23  is mounted on the side panel  44  by the follower shaft  24 . The rotary section  23  rotates back and forth between a closed position ( FIG. 1 ) and an open position in which the covering section  29  of the discharge disk  16  is substantially clear of the outlet port  31  such that substantially the entire boundary between the inlet and outlet ports is open. In a preferred embodiment, the disk rotates in a plane, substantially 90 degrees between the closed position and the open position in about 0.7 seconds. In the open position, inlet port  27  and outlet port  31  of the flush valve are in fluid communication with each other. When in the closed position, as shown in  FIG. 1 , the covering section  29  of disk  16  interrupts the fluid communication (or pressure boundary) between the inlet port  27  and the outlet port  31  and seals the outlet port  31  from receiving waste from the toilet bowl. A sleeve seal  33 , preferably made of polyethylene, is disposed adjacent to the perimeter of the outlet port  31  within the annular flange  30  of the outlet port  31 . The face of the seal is in contact with the covering section  29  and preferably has a 32 micro finish or better. When the disk  16  is in the closed position, vacuum present in the outlet port  31  and the sleeve seal  33  achieve a seal that prevents waste leakage. The covering section  29  is dimensioned to be slightly larger than seal  33  to insure complete closure. 
     In a preferred embodiment, discharge disk  16  is tear-shaped as shown in  FIG. 5 . In a tear-shaped discharge disk  16 , the rotary section  23  is the narrower trailing portion of the discharge disk  16  and the covering section  29  is the wider leading portion of the discharge disk  16 . As illustrated in  FIG. 6 , the depicted tear-shape is significantly smaller and therefore more lightweight than discharge disks  17  typically used in conventional flush valves since the non-functional material in area  49  is absent from disk  16 . The shape of the discharge disk  16  is not limited to a tear-shape. As long as the covering section  29  seals the outlet port  31  from receiving waste from the toilet bowl, other appropriate shapes, including but not limited to, round, triangular or polygon shapes, may be used with different portions of non-functional material removed. “Non-functional material” means material in the rotary section that is not necessary to maintain the integrity of that section and in the covering section that is not necessary to cover the boundary between the inlet  27  and outlet port  31 . In discharge disks having shapes without a narrower trailing portion, the rotary section  23  is that portion of the discharge disk  16  that attaches to the follower shaft  24  and the covering section  29  is that portion of the discharge disk  16  that is of a size and shape corresponding to the size and shape of the outlet port  31 . In some embodiments, the discharge disk  16  may be a combination of shapes. The rotary section  23  may be a different shape than the covering section  29 . For example, the discharge disk  16  may be the shape of a paddle with an elongated rotary section  23  resembling a handle and a wider, rounded covering section  29  resembling the shape of the face of a ping pong paddle. 
     As best seen in  FIG. 4 , the actuator shaft  22  is attached to and rotates a sensor  25  such as a potentiometer. An integrated system controller (ISC)  34  ( FIG. 1 ) attached to the side panel  44 , is electrically connected to the sensor  25  and receives data from the sensor related to the angular position of the actuator shaft  22 . Because the actuator shaft  22  also rotates a driver gear  18 , which in turn causes rotation of the follower gear  20  and disk  16 , the ISC indirectly reads the position of disk  16 . 
     Any appropriate vacuum generator may be used to provide a pressure differential in the piping attached to the flush valve outlet port  31  by drawing air out of the waste tank connected to the piping when the valve is open. However a preferred vacuum generator is a single stage centrifugal vacuum generator with a brushless DC motor. This vacuum generator is preferred because it is smaller, lighter weight and uses less power than other types of vacuum generators yet is capable of rapidly achieving target vacuum. This vacuum generator has a single impeller and preferably is powered by a high-speed brushless DC motor. 
     A preferred centrifugal vacuum generator  50  shown in  FIGS. 7-9  comprises a scroll top housing  52 , a scroll bottom housing  54 , a single impeller  56  ( FIG. 9 ), a vacuum generator controller (VGC)  57 , a DC brushless motor  58 , an intake flange  59  and an exhaust flange  61 . Thus, air is drawn from the waste tank into the vacuum generator through the intake aperture  60  formed by the intake flange  59  of the scroll top housing  52 . The impeller  56  spins the air outward into a scroll chamber that routes the air to an exhaust aperture  62  formed by the exhaust flange  61 . The housings  52 ,  54  and the impeller  56  preferably are constructed from engineered polymer to reduce their weight, to keep the design compact and to resist icing during operation in cold weather. The impeller is mounted on a motor shaft  64  ( FIG. 9 ) which is connected to the DC motor  58  and rotates within the housings  52 ,  54  at about 40,000-90,000 rpm, preferably 40,000-50,000 rpm. Because the impeller  56  is small and light weight, it can be mounted directly on the motor shaft  64  of the DC motor  58  which results in a decreased moment of inertia that allows the vacuum generator assembly to reach target speeds quickly. Furthermore, the resulting decreased moment of inertia over conventional vacuum generators used in similar applications, enables the use of a smaller DC motor and decreases the current draw. The VGC  57  controls the motor  58 , receives inputs from the level sensors (not shown) on a waste tank (not shown), and optionally controls system heaters (not shown). 
     When a user actuates a switch to flush the toilet, the switch triggers an electrical signal to the integrated system controller  34  which activates the flush valve actuator  46 . In response, the flush valve actuator causes rotation of the actuator shaft  22  and the attached driver gear  18  having drive gear teeth  19  ( FIGS. 1 and 4 ). In the preferred embodiment, the actuator shaft and driver gear are rotated substantially 90 degrees in a clockwise direction. The meshing of the drive gear teeth  19  with teeth  21  of the follower gear  20  rotates follower shaft  24  and discharge disk  16  attached to the follower shaft, substantially 90 degrees counterclockwise to the open position. In the open position, the discharge disk clears the perimeter of both inlet port  27  and outlet port  31  such that inlet port  27  is in fluid communication with the outlet port  31 . The directions of rotation may be clockwise, rather than counterclockwise if desired. Similarly, the range of rotation may also vary as desired. In other embodiments it may be desirable to provide a greater degree of rotation of the discharge disk to be sure that the disk completely clears the inlet port. 
     When the discharge disk is in the open position, the difference in pressure between the ambient air present in the toilet bowl and the lower air pressure in the piping between the toilet bowl (not shown) and the waste tank produces a suction force to evacuate the waste from the toilet bowl to the waste tank through the piping. The lower air pressure in the piping is generated by a vacuum generator (preferably generator  50  described above) at altitudes under about 16,000 feet and by atmospheric pressure outside of the plane at altitudes of about 16,000 feet and above. 
     After about one second following the opening of the flush valve, the system controller  34  signals the flush valve actuator to rotate the actuator shaft  22  and driver gear  18  substantially 90 degrees counterclockwise. This rotates follower shaft  24  and discharge disk  16  substantially 90 degrees clockwise so that the fluid connection between the inlet port  27  and the outlet port  31  is closed by the disk  16  and seal  33  is sealed from receiving more waste from the toilet bowl. 
     In case of a power failure to the flush valve actuator, the flush valve can be operated manually. To operate the flush valve manually, extension arm  32  will be rotated by the user substantially 90 degrees to open the flush valve and then back substantially 90 degrees in the opposite direction to close the flush valve. Thus, in the event that the flush valve sticks or becomes stuck in the closed position, the extension arm  32  may be rotated by the user to open the flush valve. This novel feature prevents the unsanitary back-up of waste in the toilet bowl and the potential overflow of waste from the toilet bowl into the lavatory area because the flush valve is closed. 
     All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
     The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. It should be understood that the illustrated embodiments are exemplary only, and should not be taken as limiting the scope of the invention.

Summary:
The apparatus and method of the invention provides for a flush valve for controlling the vacuum evacuation of waste from a receptacle. The flush valve comprises an inlet port for receiving the waste from the receptacle, an outlet port opposite the inlet port and in fluid communication therewith, a source of vacuum connected to the outlet port and a uniquely designed discharge disk disposed between the inlet and outlet ports for interrupting the flow of fluid therebetween. In the preferred embodiment the flush valve is integral with a latticed panel of the waste receptacle stand.