Abstract:
A canister type flush valve has an upright cup-shaped hollow float working under buoyancy forces without a captured air volume that controls the valve during a flush cycle. Hooded bleed openings at a bottom wall of the float can be sized and numbered to selectively control the closuring timing of the valve. Baffles of the hood bleed openings redirect water bleeding into the float to prevent the water from spraying up against the top of the tank. The geometry of a seal retaining groove is designed to reduce leakage at the float/seal interface. For example, the groove has an annular wall with a compound profile forming a non-cylindrical, preferably serpentine, seal contact area. The seal is backed by a slotted flange located just above the retaining groove.

Description:
STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0001]    This application is a divisional application of U.S. application Ser. No. 11/268,151, filed Nov. 7, 2005. 
     
    
     BACKGROUND OF THE INVENTION 
     CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0002]    Not applicable. 
         [0003]    The present invention relates to flush valves that control the flow of water from toilet tanks to toilet bowls. More particularly it relates to canister flush valves. 
         [0004]    Many systems for controlling the flush of toilet tank water to a toilet bowl are known, see e.g. U.S. Pat. Nos. 5,329,647 and 5,896,593. Such systems have a water inlet valve for the tank that is typically controlled by a float that senses tank water level. Depressing the trip lever moves a flush valve at the tank outlet so that water can empty from the tank through a vitreous pathway and into the bowl. As the tank water drains, the inlet valve float drops with the water level in the tank, thereby triggering inlet water flow. After sufficient tank water is drained, the flush valve closes so that the water level in the tank can be re-established. As the tank refills, the inlet valve float rises with the water and eventually closes the inlet valve to shut off the water supply. 
         [0005]    A variety of flush valves have been devised for controlling the flow of water from the tank to the bowl. One of the most common in use today is the flapper type flush valve. Flapper flush valves have a pivotal yoke that supports a large diameter stopper that seals off the tank outlet until the trip lever is tripped to start a flush cycle. The large stopper is filled with air which slows its reseating until sufficient water has been drained from the tank. Another type of flush valve has a dedicated float that mounts a main seal. When the trip lever is depressed, the float is raised and the seal unseats to allow water to flow from the tank to the bowl. One flush valve of this type is referred to as a “canister” flush valve because the valve often has a large, generally cylindrical, float that resembles a can. 
         [0006]    A concern common to many flush valves is creating and maintaining a tight seal at the tank outlet after the flush cycle is complete. The bulbous stoppers of flapper valves are generally initially good at achieving and holding a seal, but over time (e.g. years of operation) may permit leakage . Washer-like seals common in canister valves often have similar problems. 
         [0007]    If the seal leaks, water will drain from the tank to the bowl. As the tank drains, the inlet valve float will fall and cause the inlet valve to open to refill the tank. If the leak persists, the inlet valve will remain open and water will continuously drain into the bowl. This will cause the bowl to overflow, or if the bowl has overflow passages, water will pass from the bowl to the building plumbing lines. Water is wasted in either case, which is very undesirable particularly given the emphasis local communities often place on the need for low water consumption toilets. 
         [0008]    An example of a canister type flush valve is disclosed in U.S. Pat. No. 6,715,162 to Han et al. The disclosed flush valve has a valve body that mounts in the toilet tank at the outlet opening to the bowl defining a flow passage and an upper valve seat. The valve body also has an upright guide along which the float rides during a flush cycle. The float is a generally cylindrical hollow body with open ends, the upper end being above the water fill height of the tank. Water can flow through the inside of the float and through the valve body in the case of an overflow condition. The bottom end of the float has a groove about its circumference that retains a flat washer-type seal. The seal seats against the valve seat when the float is in its normal state in which the tank water is closed off from the outlet to the bowl. 
         [0009]    Sealing problems with conventional canister flush valves, arise from various factors. The primary focus in achieving a good seal in prior devices is on how well the seal mates with the valve seat. While this is important, an often overlooked leak path arises at the float/seal interface. Particularly over time with material shrinkage or degradation of the seal, water may leak through the space between the seal and the float. This can become a low resistance leak path for water in the tank because the interface is typically a short, straight vertical path. 
         [0010]    Regarding the contact of the sealing surface of the seal with the valve seat, again over time, it is possible for the seal to deform and take on a somewhat prolapsed configuration such that the seal does not mate properly with the valve seat. Thus, it is important that the seal be mounted to the float with sufficient backside (non-sealing side) support to prevent the seal from flexing away from the valve seat, without obstructing seating of the sealing side of the seal and while providing sufficient downward force on the seal so that a tight seal is maintained. Existing canister flush valves fail in one or more of these areas, and thus provide a less than optimal seal. 
         [0011]    Another concern with flush valves is controlling the water consumption of the toilet. Water consumption is largely a factor of the amount of time in which the flush valve is open. For canister type flush valves, this is dependent upon the closure timing of the float, that is, the time it takes after the float is pulled from the valve body for the float to sink and reseat the seal. At least two factors affect the closure timing of the flush valve, namely the manner in which the floatation is achieved and the manner in which the float is caused to sink. 
         [0012]    Many flush valves have an inverted cup-shaped float, with an open bottom and a closed top. When the float is pulled up by the flush trip lever, the inverted cup acts like a parachute and slows its descent by the frictional force of the water in the tank. U.S. Pat. No. 5,305,474 to Nardi et al. discloses a flush valve having such a float. Another common type of flush valve has an enclosed hollow vessel as the float. The air captured in the hollow vessel makes it buoyant so that it sinks slowly. U.S. Pat. No. 5,329,647 to Condon is an example of a flush valve with such a closed float. In both cases described above, the floats sink entirely under the force of gravity. The closure time of these valves is thus fixed for a given size and mass of the float. 
         [0013]    The valve closure time can be adjusted by allowing water to flow into the float during the flush cycle. For example, as disclosed by U.S. Pat. No. 3,172,129 to Fulton et al., one or more small bleed holes can be made in an otherwise enclosed float, such as in the bottom wall of the float. When the float is pulled upward during a flush cycle, water in the tank can flow through the bleed holes into the interior of the float, thereby increasing the overall mass of the float and causing it to sink at an increased rate so as to shorten the closure time of the valve. The size and quantity of the openings can be selected to achieve a closure rate that corresponds to a desired water consumption. 
         [0014]    One problem, however, with the use of bleed holes is that immediately after the float is moved, the pressure head in the tank is relatively high such that water will rush into the bleed holes quickly. If, unlike in the valve disclosed by Fulton et al., the float is not enclosed at the top, the rapid flow of water through the bleed holes can spray up through the float and against the underside of the tank lid. This is disadvantageous for several reasons, but primarily because of the possibility of the water spraying out the tank, or leaking down around on the rim of the tank, and onto the bathroom floor. 
         [0015]    Thus, a need exists for an improved canister type flush valve that provides for better valve closure control and effects a better seal at the tank outlet. 
       SUMMARY OF THE INVENTION 
       [0016]    The present invention is an improved canister-type flush valve for a toilet that addresses the shortcomings of the prior art discussed above. Generally, the canister flush valve has a float and seal arrangement that can be raised by a trip lever from a valve body leading to or defining the tank outlet to unseat the seal, which normally seals off the tank outlet. The float/seal interface is configured to reduce leakage between the float and seal, and seating of the seal is assisted by direct application of water pressure head in the tank. The float is also configured to improve the control of the valve closure time. 
         [0017]    In one aspect, the invention provides a canister flush valve having a valve body defining a valve seat and a flow passage leading from the valve seat toward an outlet when installed in a toilet tank. The flush valve has a float mounting a seal on a hollow longitudinally extending body with an open upper end a closed lower end. When installed in the tank, the open upper end extends above a water fill height of the tank to be in communication with ambient air, and the bottom wall at a lower end is below the water fill line. The bottom wall at least acts to restrict flow of water into the hollow body of the float during a flush cycle such that the hollow body can be suspending above the valve seat at least temporarily during the flush cycle by a buoyancy force of the water acting on an outside of the hollow body. Before and after a flush cycle the float is positioned to seat the seal on the valve seat and close off communication of tank water outside of the float with the flow passage. During a flush cycle, the float can be moved with respect to the valve body to unseat the seal and allow water within the tank to pass into the flow passage and out to the bowl. 
         [0018]    In preferred forms, the float is generally cup-shaped and oriented upright. The float can define a longitudinal overflow tube within the hollow body in communication with the open end of the hollow body and an opening in the bottom wall. The valve body can include a float guide that is received in the overflow tube, without completely obstructing flow therethrough, along which the float can travel during a flush cycle. The float is preferably molded of a rigid plastic as an monolithic structure. 
         [0019]    In another aspect the invention provides a canister flush valve with a float having a hollow body extending along a longitudinal axis and an end wall extending at an angle to the axis. The end wall has at least one bleed opening therein defining a passage into the hollow body of the float that includes travel along a path at an angle to the axis. 
         [0020]    The bleed openings can be numbered, sized, and configured to allow tank water to pass inside the float and cause it to reseat the seal before the tank is completely emptied. This assists in seating the seal by ensuring that a minimum height of water will remain in the tank to provide enough pressure head to seat the seal fully. Moreover, the number of openings as well as the opening size can be changed easily during the molding process as desired to vary closure timing for the water consumption requirements of particular toilet applications. 
         [0021]    The bleed openings can have a special hooded configuration including a baffle that is spaced from the float bottom and connected thereto by one or more longitudinal legs between which are longitudinal windows that lead to the corresponding opening in the float bottom. The baffles obstruct flow longitudinally such that when the water enters and leaves the float it must turn and pass radially through the windows. This permits bleed water to pass into the float after a flush cycle is initiated, and then drain out of the float after the seal is reseated, but prevents water rushing into the float from spraying up through the float against the tank lid. 
         [0022]    In still another aspect the invention provides a canister flush valve with a float having a seal retaining portion with a compound profile defined by at least one non-cylindrical annular surface. The seal has a peripheral surface mating with the compound profile of the float seal retaining portion to mount to the float for seating against the valve seat. 
         [0023]    The float can extend along a longitudinal axis, and the seal retaining portion of the float holds the seal in a radial orientation, generally perpendicular to the longitudinal axis. The compound profile is then defined by an annular longitudinal wall at the seal retaining portion of the float. 
         [0024]    The seal can be an annular seal, and the seal retaining portion of the float can be a groove extending about the periphery of the float in the radial direction and opening outward. The annular wall at the closed end of the groove defines the compound profile. An inner periphery of the seal is disposed in the groove and an outer periphery is out of the groove so that the seal can seat against the valve seat. Preferably, the inner peripheral surface is defined by the inner diameter of the seal. 
         [0025]    The compound profile of the seal retaining portion, or groove, and the mating inner periphery of the seal define at least inter-digitated joint, such as a tongue and groove. In particular, either the compound profile or the seal or both can have at least one annular projection or peak that meshes with a valley in the other part. The compound profile and/or inner periphery of the seal can be defined by a continuous, non-linear annular surface. In each case, the continuous curved surface can define one or more convex peaks and one or more concave valleys. For example, the annular wall of the seal retaining groove can define a convex annular peak longitudinally between two adjacent concave valleys, and the mating periphery of the seal can define an annular concave groove between two annular convex peaks. The resulting interface thus provides a continuous convoluted contact area that greatly resists the passage of liquid therebetween. 
         [0026]    It should be noted that the precise seal interface configuration can be of any suitable complex geometry provided that at least a portion of the seal contact area is non-cylindrical. The interface configuration also preferably has at least two curved and/or linear portions which define an included angle therebetween other than 180 degrees. Thus, the float seat retaining portion profile and mating seal periphery can be formed by single convoluted surface as well as any number of linear and/or curvilinear surfaces such that at least a portion of the single surface or one of the plurality of surfaces is not parallel to the longitudinal axis of the float. Annular peaks and/or valleys with rectilinear cross-sections, such as square or V-shaped, could thus be used. 
         [0027]    Moreover, it should be noted that both the seal and float need not be formed with a compound profile, but instead one of the components could be made of a flexible material that can conform to the compound profile of the other component. For example, in one preferred form, the seal is made of a flexible elastomer material that has a simple straight longitudinal profile at its inner diameter that upon being mounted to the float will conform to the compound profile of the float. 
         [0028]    In still another aspect, the float/seal interface, the float can have an annular, generally radially extending, seal backing flange at a side of the seal and seal retaining portion opposite the valve seat of the valve body, e.g., longitudinally above the seal. The flange acts as a seal backstop by providing structural support to the outer periphery of the seal should it flex longitudinally away from the valve seat. It also acts to reduce drag on the seal in the longitudinally downward direction when the float is pulled up by the trip lever, and thereby helps maintain a tight connection at the float/seal interface. 
         [0029]    The flange can include an opening, preferably multiple openings in the form of open-ended slots (for ease of manufacture) that are spaced apart along the flange. These slots better expose the non-sealing side of the seal to the tank water so that the water pressure head in the tank can act directly on the seal to assist in tightly seating the seal. By providing a backing flange to support the seal, the seal can be made of a soft, flexible material that conforms well to the valve seat. The soft seal also seats quietly, and since the flange is there to backstop the seal, there is no need for contact between two hard parts of the float and valve body, thereby reducing valve closure noise. 
         [0030]    These and other advantages of the invention will be apparent from the detailed description and drawings. What follows are one or more preferred embodiments of the present invention. To assess the full scope of the invention the claims should be looked to as the preferred embodiment(s) are not intended as the only embodiment(s) within the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0031]      FIG. 1  is a partial sectional front view of a canister flush valve assembly according to the present invention mounted in a toilet tank; 
           [0032]      FIG. 2  is a vertical sectional view of the canister flush valve shown in  FIG. 1  in its normally closed position; 
           [0033]      FIG. 3  is a sectional view similar to that of  FIG. 2  albeit with the canister flush valve shown in an open position to allow water in the toilet tank to enter a toilet bowl during a flush cycle; 
           [0034]      FIG. 4  is an enlarged partial sectional view taken along arc  4 - 4  of  FIG. 2  showing the canister flush valve seal against the valve seat in the closed position of  FIG. 2 ; 
           [0035]      FIG. 5  is a partial sectional view similar to  FIG. 4  showing a compound profile of a seal retaining groove with the valve seal removed; 
           [0036]      FIG. 6  is an exploded perspective view of the canister flush valve float, seal, and valve body; 
           [0037]      FIG. 7  is a top plan view of the float; and 
           [0038]      FIG. 8  is an enlarged partial sectional view taken along line  8 - 8  of  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0039]    Referring now to the drawings,  FIG. 1  shows a toilet  10  which includes a water tank  12  and a bowl section (not shown). The tank  12  has a horizontal bottom wall  16  with an outlet opening  18 , which leads to a channel in an upper rim of the bowl. Mounted inside the tank is the usual water supply pipe  20  with a float  22  operated supply valve  24  for controlling the flow of supply water into the tank  12 . A flush valve assembly  26  is mounted inside the tank  12  over the outlet opening  18  to control the flow of water from the tank  12  to the bowl during a flush cycle. 
         [0040]    Referring to  FIGS. 1 ,  2  and  6 , the flush valve assembly  26  is mounted vertically upright in the tank  12  and primarily includes a valve body  28 , a float  30  and a seal  32 . The valve body  28  and float  30  are preferably a non-corrosive material, such as a suitable plastic. The seal can be made of a flexible material, for example a suitable elastomer, such as vinyl, EPDM rubber, or silicon, which has particularly good chemical/corrosion resistance properties. The lower end of the valve body  28  extends through the tank outlet opening  18  can has external threads that engages a gasket  33  and a threaded retaining nut  34  that threads tightly against an underside of the tank bottom wall  16 . The valve body  28  also has a flange  36  that clamps a suitable gasket  38  against an upper side of the bottom wall  16  and mounts the flush valve assembly  26  to the tank  12 . 
         [0041]    In an alternate configuration not shown, the lower end of the valve body can have three prongs that engage the underside of the bottom wall  16  to mount the flush valve assembly to the tank. This connection is similar to that disclosed in U.S. Pat. No. 4,433,446, which is assigned to the assignee of the present invention, and the disclosure of which, particularly FIGS.  2  and  4 - 6  and the related description therein, is hereby incorporated by reference. 
         [0042]    The valve body  28  defines a generally cylindrical flow path leading from a circular valve seat  40  at it is upper end through the tank outlet opening  18 . The valve body  28  and flow passage are generally concentric with a longitudinal axis  42 . Bracing  44  extend from the outer wall of the valve body to support a central opening  46  that receives a mounting stem  48  of a separate guide post  50  extending up from the valve body along the axis  42 . The opening  46  is generally oblong to allow two small ears (not shown) on the stem  48  to pass through the opening when the post  50  is oriented properly and with a ¼ turn the ears restrict separation of the post  50  from the valve body  28 . The post  50  has a generally x-shaped upwardly tapering cross-section with a central void  52  and ring  54  at an upper end. A lower part of the stop  56  fits down into the void  52 , again with notches and ears (not shown) allowing insertion and removal in one orientation but otherwise restricting separation of the stop  56  from the post  50 . The stop  56  has a large diameter flange section  58  that extends radially, perpendicular to the longitudinal axis  42 , further than the post  50 . The flange section  58  backs a gasket  59 . The stop  56  is captured in the top of the post by a ¼ turn ear and notch arrangement (not shown). The stop  56  is hollow and open ended so that a bowl refill line (not shown) coming from the supply inlet valve can be attached to a fitting  55  of the stop  56 . 
         [0043]    The float  30  is an upright, cup-shaped unitary body integrally formed with an outer longitudinal cylindrical wall  60  with an upper end open to the ambient air above the tank water, a radial bottom wall  62  and a central longitudinal overflow tube  64  that fits about the post  50  to mount the float  30  to the valve body  28 . Should the tank be filled above its water fill height, overflow water will spill over the open upper end of wall  60  to the interior of the float. The overflow water can drain from the float and out of the tank through the flow passage in the valve body  28  through small bleed openings  70  in the bottom wall  62 . If the overflow water enters the float faster than it is drained, it will begin to fill the float until it reaches the open upper end of the overflow tube  64 , after which it will drain through the overflow tube  64  (around the post  60 ) and exit through an opening  63  in the bottom wall  62  at the lower end of the overflow tube  64 . Also, after a flush, water from the refill line fills the bowl by passing from the line through the stop  56  and the overflow tube  64  (again around the post  50  and out the large, central opening in the bottom wall  62 ) and the flow passage of the valve body  28 . 
         [0044]    The overflow tube  64  of a lesser longitudinal dimension than the post  50  so that the float  30  can travel longitudinally up and down the post  50  during a flush cycle. The float  30  is captured between the valve seat  40  and the large diameter section  58  of the stop  56 . The gasket  59  seats against the top edge of the overflow tube  64  and reduces associated contact noise. The float  30  is linked to the trip lever  66  of the toilet by a lever arm  67  and a chain  68  connected to one of two longitudinally spaced tabs  69  at each “side” of wall  60 . 
         [0045]    As shown in  FIGS. 2 ,  4 ,  7  and  8 , the bottom wall  62  has five spaced apart “hooded” bleed openings  70 . The hooded bleed openings  70  are integral structures including a radial baffle  72  spaced up from the bottom wall by three longitudinal legs  74 . Longitudinal windows  76  are formed between the baffle  72 , legs  74  and bottom wall  62  to provide access to the small openings  78  in the bottom wall. The bleed openings  70  allow for drainage of overflow water (as mentioned above), but primarily are used to control the closure timing of the float, and thereby the amount of water consumed in a flush cycle, by allowing a controlled amount of water to flow up into the interior of the float  30  during a flush cycle. The water inside the float  30  will add mass to the float so that it tends “sink” more rapidly than without it. This works to reseat the seal  32  quicker so that there is a minimum water level in the tank that provides a pressure head sufficient to firmly reseat the seal  32 . The baffles  72  of the bleed openings  70  obstruct the longitudinal path of the incoming bleed water, causing it to be redirected radially through the windows  76  after passing through the openings  78  in the bottom wall  62 . This allows the desired flow into and out of the float  30 , but prevents the incoming water from spraying up through the float and hitting the underside of the tank lid, thereby avoiding any associated noise and leakage around the tank lid. 
         [0046]    As mentioned, the bleed openings are used primarily to control the closure timing of the valve, that is, to control the time the float is off of the valve body and the seal is unseated from the valve seat. The quantity and size of the bleed openings can be selected to vary the flow volume into the float, and thereby the overall mass of the float, during the flush cycle. In the preferred embodiment described herein, there are five bleed openings in the bottom wall  62  of the float spaced equally around the axis  42 , including two ¼″ openings, two 3/16″ openings and one ⅛″ opening. Since the preferred float is a unitary molded plastic structure, the openings can be easily formed closed or open during the molding process to achieve the desired closure timing. The smallest opening provides fine tuning of the closure time, with such a ⅛″ opening causing a delay in closure time corresponding to adding about 0.03 gallons to the flush. The other openings have a proportional effect on the closure time and water consumption. 
         [0047]    Referring now to  FIGS. 2-5 , the lower end of the float  30  defines an annular circumferential seal retaining groove  80  opening outwardly in a radial direction. The seal  32  fits about the float  30  concentric with axis  42  and is retained in the groove  80  in a generally radial orientation. Adjacent to the groove  80  is a circumferential, radially extending seal backing flange  82  located to a longitudinal side of the groove  80  opposite the valve seat  40 . 
         [0048]    The backing flange  82  extends radially outward past that of the valve seat  40  about the distance of extension of the seal  32 . The backing flange  82  acts as a backstop for the outer portion of the seal  32  that is not retained in the groove  80 . Should the seal  32  be flexed away from the valve seat  40 , such as if the float were to become cocked, the rigid backing flange  82  will resist further movement so that the seal  32  will seat against the valve seat  40 . The presence of the backing flange  82  allows a softer, more flexible material to be used for the seal  32 , which can better conform to the valve seat and provide better sealing. The softer seal also reduces valve noise as the valve closes, since the contact is between the seal and the valve seat and no contact is required between rigid (plastic on plastic) structures of the float and the valve body to limit downward travel of the float. Moreover, the flange  82  shields the seal  32  to reduce the drag on the seal during the upstroke of the float  30 , which reduces loosening of the joint at the float/seal interface. 
         [0049]    Another important feature of the backing flange  82  is that it has a number of slots  84 , see  FIGS. 7 and 8 , spaced about the axis. In the preferred embodiment shown, there are six slots oriented in three parallel columns in the view shown in  FIG. 7 . The slots serve to better allow the water pressure head in the tank to act directly in a longitudinal downward direction on the seal  32  so that the pressure head will apply a sealing force tending to seat the seal  32  on the valve seat  40 . The slots also break up any suction between the underside of the flange and the upper side of the seal should the seal be pushed back against the flange, thus allowing the seal to return to its normal position. While slots that open at the outer edge of the flange  82  are preferred because of the ease of manufacture, other through holes and opening orientations could be used. 
         [0050]    Referring again to  FIGS. 4 and 5 , the closed end of the seal retaining groove  80  is defined by an annular wall  96  having a compound profile. The term “compound profile” as used herein refers in general to a any profile defining a non-cylindrical annular surface when revolved about an axis, and more particularly to a profile defined by a single continuous curve or the combination of multiple intersecting linear and/or curvilinear segments. When formed of multiple linear/curvilinear segments, adjacent segments should form an included angle of other than 180 degrees. In the case of a single curve, at least two adjacent sections of the curve should have differing radii of curvature or intersect an inflection point so that the adjacent sections have different concavity. Thus, under one satisfactory meaning of compound profile, the profile would form a continuous curve defining one or more convex peaks and one or more concave valleys. Another satisfactory meaning of this term is a profile that defines a path which defines a bend or included angle of more than 90 degrees, for example a convoluted serpentine path. While various specific configurations fall within the meaning of the term, a compound profile will result in an annular float/seal interface with a contact area that resists the passage of liquid therebetween better than the contact area associated with a straight linear profile. 
         [0051]    Since the seal  32  is preferably a flexible, stretchy elastomer, its inner periphery or diameter  98  will conform to the compound profile of the groove wall  96 . As such, it need not be machined or otherwise formed to have a permanent mating compound profile of its own. The seal  32  can thus have an inner diameter with a simple, linear profile defined by a cylindrical surface. However, if a less conformable material is used, the seal can also have a compound profile selected to mate with that of the groove wall  96 . 
         [0052]    In the illustrated embodiment, the annular groove wall  96  defines a compound profile, when taken in the longitudinal direction as shown in  FIG. 5 , formed of a single continuous curve, with two inflection points, defining a concave valley  100 , a convex peak  102  and another concave valley  104 , the peaks and valleys extending in a radial direction and the valleys  100  and  104  being longitudinally above and below the peak  102 , respectively. As shown in  FIG. 4 , the inner diameter  98  of the seal  32  conforms to the compound profile to create mating peaks and valleys. 
         [0053]    The compound profile thus creates an inter-digitated joint, such as a tongue and groove, following a convoluted, serpentine longitudinal path. When revolved about the axis  42 , the convex peaks become annular ribs or peak surface and the concave valleys become annular grooves or valley surfaces. The seal contact area thus occurs between convoluted annular surfaces, resulting in a float/seal interface that is highly resistant to liquid migration. 
         [0054]    Resistance to liquid migration through the float/seal interface is furthered by virtue of the contact area between the radial surfaces (at the top and bottom sides) of the seal  32  and the groove  80 . Moreover, the compound profile of the groove annular wall  96  includes an oblique angled linear segment, or chamfer,  106  that forms an annular oblique surface adding further complexity to the float/seal interface so as to even better resist liquid migration, as well as to serve as a ramp facilitating assembly of the seal  32  into the groove  80 . The top portion of the ramp also helps position the seal to ensure that the convex/concave surfaces are fully mated. 
         [0055]    The peak  102  and the chamfer  106  thus provide multiple distinct pressure points creating multiple height seal contact locations spaced apart in the longitudinal direction. Thus, in the preferred embodiment illustrated in the drawings, for tank water to migrate around the seal it would have to travel between the seal and float radially along the upper side of the seal, turn 90° and travel longitudinally through the valley  100 , turn 90° in the opposite direction around the peak  102 , turn back 90° through valley  104 , then turn along the chamfer  106  and finally travel radially past the underside of the seal. 
         [0056]    Regarding the operation of the flush valve, prior to performing a flush operation, the flush valve is in the position shown in  FIGS. 1 and 2 , with the float  30  and seal  32  seated on the valve seat  40  and the water level in the tank  12  being “full”. Actuating the trip lever pulls the float  30  upwardly sufficient to cause it to unseat the seal  32  from the valve seat  40  and be pulled up into the position shown in  FIG. 3 . Since the float body is open at the upper end such that its interior is in communication with the ambient air above the tank water, the float is suspended not by a trapped air volume, but instead entirely by the buoyancy force of the water acting on the outer surfaces of walls  60  and  62 . Water in the tank  12  can flow through the valve body  28  and out through the tank outlet opening  18  to the bowl. Water and waste in the bowl are evacuated to plumbing waste lines in the usual manner through a trap (not shown). Tank water flows into the float  30  through the bleed openings  70 , and when sufficiently heavy and the tank  12  drains low enough, the weight of the float  30  causes it to fall under gravity and seat the seal  32  against the valve seat  40 . The flush cycle completes after the tank  12  is refilled with water sufficient to trip the supply valve. 
         [0057]    It should be appreciated that merely preferred embodiments of the invention have been described above. However, many modifications and variations to the preferred embodiments will be apparent to those skilled in the art, which will be within the spirit and scope of the invention. Therefore, the invention should not be limited to the described embodiments. To ascertain the full scope of the invention, the following claims should be referenced.