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FIELD OF THE INVENTION 
     The present invention generally relates to toilets and, more particularly, to vacuum toilet Systems. 
     BACKGROUND OF THE INVENTION 
     Vacuum toilet systems are generally known in the art for use in both vehicle and stationary applications. A vacuum toilet system typically comprises a bowl for receiving waste having an outlet connected to a vacuum sewer line. A discharge valve is disposed between the bowl outlet and vacuum sewer line to selectively establish fluid communication therebetween. The vacuum sewer line is connected to a collection tank that is placed under partial vacuum pressure by a vacuum source, such as a vacuum blower. When the discharge valve is opened, material in the bowl is transported to the sewer pipe as a result of the pressure difference between the interior of the bowl and the interior of the sewer line. Conventional vacuum toilet systems also include a source of rinse fluid and a rinse fluid valve for controlling introduction of rinse fluid into the bowl. 
     Conventional discharge valves are overly complicated to assemble. Such valves typically have a movable valve member linked to an actuator that operates the valve member between open and closed positions. The linkage between the valve member and the actuator often includes pivoting arms, joints, and other components which increase the complexity of valve assembly. In addition, gearing is often needed to slow the actuator speed to the desired valve actuation speed. Gear heads having four or more stages are often required to obtain the desired speed. Each stage, however, introduces friction and other losses that decrease the efficiency of power transmission from the actuator to the valve member. 
     In addition, conventional discharge valves undesirably generate a high noise level during a flush operation. When the discharge valve opens in response to a flush command, a significant amount of air, in addition to waste material and rinse fluid, is pulled into the sewer line. The air flows through a relatively narrow bowl outlet, which creates the noise. The noise may further be amplified by the shape of the toilet bowl. Apparatus is known for reducing the noise by introducing a secondary source of air into the sewer pipe during a flush cycle. This apparatus, however, requires a separate valve and actuator, thereby increasing the cost and complexity of the toilet. 
     Still further, vacuum toilet systems in general and discharge valves in particular are overly difficult and time consuming to maintain. Maintenance concerns are particularly significant in aircraft applications, in which a number of sub-systems are installed on board. According to general practice in the airline industry, each sub-system includes one or more components which must be replaced in the event of failure, such replacement components being commonly referred to as line replaceable units (LRUs). Presently, the entire vacuum toilet is defined as the LRU for the vacuum toilet system. As a result, an airline must stock one or more replacement toilets in the event of a toilet failure, so that the replacement toilet may be swapped in for the faulty toilet. A “bench test” is then performed on the faulty toilet to determine which components have failed in the toilet. The faulty components are then repaired or replaced (which may include significant disassembly and reassembly of the toilet) so that the repaired toilet may be reused on another aircraft. 
     Each of the steps performed during a toilet repair is overly difficult and time consuming. To remove an entire toilet assembly from an aircraft requires disassembly of at least four self-locking mounting fasteners, an electrical connection, a grounding strap, a potable water line connection, and a waste discharge pipe connection. Each connection may be difficult to access, and may require a particular tool in order to loosen and disconnect. The same connections must then be reconnected for the replacement toilet. 
     Even if it were possible to remove and replace a single toilet component, it would be overly difficult and time consuming to do so. Removal of a component would require disconnection of several wires and pipes, and the components are often located in areas which are difficult to access. Furthermore, it would be difficult to diagnose whether one component or several components had failed. There exists a multitude of combinations of simultaneous component failures, which may lead to trouble-shooting errors and the replacement or repair of non-faulty components. 
     Conventional discharge valves also use seals which are difficult to install and replace. As noted above, a discharge valve typically has a moving valve member disposed inside a housing. Seals are typically provided inside the housing to prevent leaks between the valve member and the upstream and downstream sides of the housing. As a result, the valve housing must be disassembled to remove and replace a faulty seal. 
     Conventional vacuum toilets further fail to provide adequate feedback regarding valve position. Conventional discharge valves are typically driven by an electric motor actuator having mechanical limit switches and signal switches to control valve position. Such a switch is overly complicated to use and maintain. The switches must be precisely set to trigger at the appropriate time, and special tooling is often required to set the switch. In addition, by locating the switches in the actuator, they are subject to mechanical wear and contact erosion, which may alter the setting of the switch, thereby requiring re-setting. Furthermore, lubricant or other materials may migrate to the switches, causing switch failure. Most importantly, the conventional apparatus is unreliable since valve position is inferred from the actuator position. As a result, the conventional approach is not responsive to various failure situations where the actuator may be operable but the valve is not, such as when the linkage connecting the actuator to the valve is broken or defective. 
     SUMMARY OF THE INVENTION 
     In accordance with certain aspects of the present invention, a discharge valve is provided for use in a vacuum toilet system having a waste receptacle defining an outlet and a sewer line placeable under partial vacuum. The discharge valve comprises a housing defining an inlet and an outlet, and a rotatable discharge valve member disposed in the housing for selectively establishing fluid communication between the inlet and the outlet, wherein a periphery of the valve member being formed with a series of gear teeth. An actuator has a rotatable gear adapted to engage the periphery of the discharge valve member. 
     In accordance with additional aspects of the present invention, a discharge valve is provided for use with a vacuum toilet system having a waste receptacle defining an outlet and a sewer line placeable under partial vacuum. The discharge valve comprises a housing defining a flush valve inlet fluidly communicating with the waste receptacle outlet, a flush valve outlet fluidly communicating with the sewer line, an air intake valve inlet fluidly communicating with ambient air, and an air intake valve outlet fluidly communicating with the sewer line. A movable valve member is disposed in the housing and defining first and second apertures, the valve member having a closed position in which the valve member obstructs fluid communication between the flush inlet and flush outlet, and between the air intake valve inlet and air intake valve outlet, and an open position in which the first and second apertures establish fluid communication between the flush inlet and flush outlet, and between the air intake valve inlet and air intake valve outlet. 
     In accordance with further aspects of the present invention, a discharge valve provided for use with a vacuum toilet system having a waste receptacle defining an outlet and a sewer line placeable under partial vacuum. The discharge valve comprises a housing defining a flush valve inlet fluidly communicating with the waste receptacle outlet and a flush valve outlet fluidly communicating with the sewer line. A rotatable valve member is disposed in the housing and defines a first aperture. The valve member has a closed position in which the valve member obstructs fluid communication between the flush valve inlet and the flush valve outlet, and an open position in which the first aperture establishes fluid communication between the flush valve inlet and flush valve outlet. A first seal is provided having a cylindrical wall sized for insertion from an exterior of the housing into the flush valve inlet, the cylindrical wall having a bottom edge adapted to engage and seal with the rotatable valve member. 
     In accordance with still further aspects of the present invention, a discharge valve is provided for use in a vacuum toilet system. The discharge valve comprises a housing defining a discharge valve inlet and a discharge valve outlet. A valve member is disposed inside the housing, the valve member being movable between a closed position in which the valve member obstructs fluid communication between the discharge valve inlet and the discharge valve outlet, and an open position in which fluid communication is established between the discharge valve inlet and the discharge valve outlet. A sensor is provided for detecting position of the valve member, the sensor being located outside of the housing. 
     In accordance with yet additional aspects of the present invention, a discharge valve is provided for use in a vacuum toilet system having a bowl defining an outlet and a sewer line placeable under partial vacuum. The discharge valve comprises a housing defining a discharge valve inlet adapted for fluid communication with the bowl outlet and a discharge valve outlet adapted for fluid communication with the sewer line. A seal is disposed inside the discharge valve outlet, and a disk is disposed inside the housing and has first and second apertures connected by a slot. The first aperture, second aperture, and slot divide the disk into first and second disk halves, and the disk is rotatable between a closed position, in which one of the first and second disk halves engages the seal to obstruct fluid flow, and an open position in which one of the first and second apertures is aligned with the seal to allow fluid flow therethrough. The slot allows the first and second disk halves to deflect in response to partial vacuum at the discharge valve outlet to more reliably engage the disk with the seal in the closed position. 
     Other features and advantages are inherent, in the apparatus claimed and disclosed or will become apparent to those skilled in the art from the following detailed description and its accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B are perspective views of a vacuum toilet incorporating a discharge valve in accordance with the present invention. 
     FIG. 2 is a schematic diagram of the vacuum toilet of FIG.  1 . 
     FIG. 3 is an enlarged perspective view of a valve set, including the discharge valve, incorporated into the vacuum toilet of FIG.  1 . 
     FIGS. 4A and 4B are perspective views of the discharge valve. 
     FIG. 5 is an exploded perspective view of the discharge valve. 
     FIG. 6 is a side elevation view of an alternative discharge valve member embodiment. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A vacuum toilet  10  is illustrated in FIGS. 1A,  1 B and  2  having a valve set  8  with a discharge valve  70  in accordance with the present invention. The vacuum toilet  10  includes a bowl  36  for receiving waste material connected to the valve set  8 . In the preferred embodiment, the bowl  36  is supported by a frame  20  to form a replaceable bowl assembly, as described in greater detail in commonly owned and co-pending U.S. patent application Ser. No. 09/713,861, entitled “Toilet Bowl Assembly”, incorporated herein by reference. The vehicle is provided with a sewer line  11 , a vacuum tank  13  connected to the sewer line  11 , and a vacuum source (not shown) for placing the vacuum tank  13  under partial vacuum pressure. The vehicle further includes a source of rinse fluid  15  connected to a rinse fluid supply line  19 . At least one rinse fluid dispenser, such as nozzles  46 , is provided inside the bowl  36  for directing rinse fluid over the surface of the bowl. A rinse fluid pipe  35  connects the valve set  8  to the nozzles  46 . 
     As shown in FIG. 3, the valve set  8  comprises four sub-components: the discharge valve  70 , a rinse valve  72 , a flush control unit (FCU)  74 , and an actuator  76 . The preferred valve set is described in greater detail in commonly owned and co-pending U.S. patent application Ser. No. 09/713,870, entitled “Valve Set for a Vacuum Toilet”, incorporated herein by reference. While the discharge valve  70  is described and illustrated herein as integrated into the valve set  8 , it will be appreciated that the discharge valve  70  may be provided as a separate, independent component, without departing from the spirit and scope of the present invention. 
     The discharge valve  70  includes a discharge valve housing  78  divided into two halves  78   a,    78   b.  As best shown in FIGS. 4A and 4B, the housing  78  includes a pair of inlets  79 ,  80  formed in the housing half  78   a  aligned with a pair of outlets  81 ,  82  formed in the housing half  78   b.  The housing  78  further defines a chamber for receiving a discharge valve member, such as valve disk  83 . An axle  84  is attached to the valve disk  80  and has two ends  84   a,    84   b.  Holes are formed in the housing halves  78   a,    78   b  sized to receive the axle ends  84   a,    84   b,  respectively, so that the disk  83  is supported for rotation about the axle  84 . In accordance with certain aspects of the present invention, the periphery of the disk  83  is formed with gear teeth  85 , and a pair of apertures  86 ,  87  are formed through the disk  83 . The apertures  86 ,  87  are spaced so that both register simultaneously with the associated inlet/outlet pairs  79 / 81 ,  80 / 82  as the disk  83  rotates. In the illustrated embodiment, the apertures  85 ,  86  and associated inlet/outlet pairs  79 / 81 ,  80 / 82  are spaced 180 degrees apart. 
     According to the illustrated embodiment, the inlet  79  is connected to one end of a transfer pipe  44 , with the other end of the transfer pipe being attached to an outlet  42  of the bowl  36 . In the preferred embodiment, the transfer pipe  44  includes a fitting  47  (FIG. 1A) adapted to frictionally and sealingly engage the bowl outlet  42 , so that the transfer pipe  44  may be quickly and easily attached and removed from the bowl outlet  42 . An air intake check valve  45  is attached to the other inlet  80 , and is oriented to allow fluid to flow into the inlet  80  while preventing fluid from discharging out of the check valve  45 . A U-shaped outlet pipe  12  (FIG. 1B) has a first end connected to the outlet  81  and a second end connected to the outlet  82 . The outlet pipe  12  further has a branch  17  leading to a discharge pipe  21 . In the preferred embodiment, the branch  17  includes a pair of spaced pins and the discharge pipe  21  includes a pair of J-shaped slots positioned to engage the pins, so that the discharge pipe  21  is removably attached to the branch  17 . Furthermore, when the pins and J-shaped slots are spaced 180 degrees apart, the discharge pipe  21  may be positioned for either right- or left-handed discharge simply by rotating the discharge pipe  21  before attachment, without requiring changes to the other toilet components. The free end of the discharge pipe  21  is adapted for releasable connection to the sewer line  11 , such as with a clam shell coupling (not shown). 
     In operation, when the disk apertures  86 ,  87  are aligned with the inlet/outlet pairs  79 / 81 ,  80 / 82 , the discharge valve  70  not only transfers waste from the transfer pipe  44  to the sewer line  11 , but also pulls additional air into the sewer line  11  through the air intake check valve  45 . The additional air intake reduces noise that is normally generated during a flush. 
     The actuator  76  is provided for driving the valve disk  83 . As best shown in FIG. 4A, the actuator  76  includes a spur gear  90  enmeshed with the gear teeth  85  formed about the periphery of the disk  83 . The spur gear  90  is mounted to a rotatable shaft  92 , and a drive is provided for rotating the shaft  92 . The FCU  74  is operably coupled to the actuator  76  to control operation of the actuator. According to the illustrated embodiment, the disk  83  may be rotated in a single direction by ninety degree increments to open and close the discharge valve  70 . Alternatively, the disk  83  may also be reciprocated back and forth across a ninety degree arc to open and close the valve  70 , or the disk  83  may be controlled in other manners according to other disk designs and layouts. 
     In accordance with additional aspects of the invention, external seals are provided for preventing fluid leaks between the disk  83  and valve housing  78 . As best shown in FIG. 5, four seals  95  are provided each having a cylindrical wall  96  sized for insertion into the inlets  79 ,  80  and outlet  81 ,  82 . Each seal  95  further includes a lip  97  that engages an outside surface of the housing  78  to limit travel of the cylindrical wall  96  into the housing  78 . The cylindrical walls  96  have a height sufficient to engage and seal with the disk  83  when fully inserted into the housing  78 . The sealing engagement between the seals  95  and disk  83  is maintained during rotation of the disk  83  to prevent fluid leakage. The seals  95  may be inserted and removed from the outside of the housing  78 , thereby obviating the need to disassemble the discharge valve housing  78  for a seal replacement. The seals  95  are preferably formed of ultra-high molecular weight polyethylene. 
     Vacuum pressure present in the outlet pipe  12  will act on a closed disk  83  to pull the disk  83  toward the seals  95  inserted in the outlets  81 ,  82 , thereby energizing the seals. Accordingly, it will be appreciated that the seals  95  inserted in the inlets  79 ,  80  do not technically seal with the disk  83 , but instead help to center the disk  83  inside the housing  78 . In an alternative disk embodiment illustrated at FIG. 6, a split disk  183  is provided to further enhance the seals formed at the outlets  81 ,  82 . The disk  183  is formed with a pair of apertures  186 ,  187  connected by a slot  180 . The slot  180  divides the disk  183  into two disk halves  184 ,  185  that are more easily flexed in a direction normal to the plane of the disk  183  (or into and out of the page as shown in FIG.  6 ). Because of the increased flexibility, the disk halves  184 ,  185  are more responsive to the vacuum pressure in the outlet pipe  12 , so that the outlets  81 ,  82  are more reliably sealed. 
     The FCU  74  comprises a housing  150  attached to the discharge valve housing half  78   b  opposite the rinse valve  72  (FIG. 3 ). The housing  150  encloses one or more circuit boards  155  (FIG. 5) for controlling operation of the discharge valve  70  via the actuator  76 . Because the FCU  74  is located proximal to the actuator  76 , the number of wires needed between the FCU  74  and actuator  76  is reduced. 
     In addition, the FCU housing  150  houses a position sensor for determining the position of the disk  83 . As best shown in FIG. 4A, magnets  152  are attached to the axle end  84   b  of the disk  83 . The axle end  84   b  extends into the FCU housing  150 , so that the magnets  152  are positioned proximal the control board. Hall effect switches  154  are provided directly on the circuit board for sensing the magnets  152  and thus determining the rotational position of the disk  83 . In the illustrated embodiment, a pair of magnets  152  are attached to the axle end  84   b,  and a pair of hall effect switches  154  are attached to the circuit board. The switches  154  actuate between on and off positions depending on the proximity of the magnets, thereby indicating the position of the disk  83 . As a result, the position of the disk  83  is directly sensed rather than inferring disk position based on actuator position. In addition, the switches  154  are located inside the FCU housing  150  and are therefore isolated from contamination due to lubrication or other material. 
     From the foregoing, it will be appreciated that the discharge valve of the present invention has a simplified valve member drive due to the gear teeth formed about a periphery of the discharge valve member. In addition, the discharge valve simultaneously opens the drain and secondary air passages, and may be operated in a single direction. Furthermore, the seals are easily removed from an exterior of the valve, thereby facilitating replacement. 
     The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modifications would be obvious to those skilled in the art.

Summary:
A discharge valve is disclosed for use in a vacuum toilet system having a waste receptacle defining an outlet and a sewer line placeable under partial vacuum. The discharge valve comprises a housing defining an inlet and an outlet and a rotatable discharge valve member disposed in the housing for selectively establishing fluid communication between the inlet and the outlet. A periphery of the disk valve member being formed with a series of ear teeth. An actuator is provided having a rotatable spur gear adapted to engage the periphery of the discharge valve member.