Patent Publication Number: US-2006016479-A1

Title: Backflow prevention valve

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/590,362, filed Jul. 23, 2004. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates generally to fluid control valves, and more particularly to a valve that is particularly well configured to prevent fluid backflow in systems configured for relatively high flow rates and pressures. The present valve may be readily adapted for use in both wet and dry barrel fire hydrants to prevent contamination of the water supply therethrough, or may be adapted to other relatively high pressure and high flow fluid systems requiring one-directional flow and backflow prevention.  
      2. Description of the Related Art  
      Fire hydrant systems are generally connected to a central municipal high pressure water supply source. The hydrants themselves are configured to provide relatively large fluid flows, as necessary to quench a large fire. Hydrants are nearly universally readily accessible, in order to provide for rapid connection of hoses and opening of the hydrant valve since time is critical in fighting fires. Hydrants are generally not equipped with backflow prevention valves for the main water flow, as in the past there has been no apparent reason that such valves would be needed in hydrant installations.  
      The ready accessibility to the water supply by means of fire hydrants has resulted in various users tapping into the water supply for various reasons. In many cities, street sweepers and construction water tank trucks will have their water tanks refilled by means of readily available municipal hydrants. This is generally not of great concern, as it does not affect the water supply to any significant degree.  
      However, the access to fire hydrant water supplies by non-firefighting personnel leaves the door open for potentially tragic misuse of such a system. It has occurred to the present inventor that one or more terrorists could easily contaminate a municipal water supply, merely by pumping contaminated water or other liquid back into the water supply through an easily accessible hydrant. A terrorist would need nothing more than a relatively small tanker truck or water tank on a trailer, and a pump providing higher pressure than the municipal water supply in the hydrant system. Contaminated water or other liquid could be pumped back into the municipal water supply, thereby contaminating the entire municipal water supply, or at least a good portion of it, depending upon the contaminant and its spread or proliferation in the water supply.  
      Accordingly, the present inventor has developed a solution to this potential problem by means of a backflow prevention valve which is readily adaptable for installation in existing fire hydrants of various types, and which may be adapted to other fluid flow systems as well. The present valve essentially comprises a series of generally triangular vanes which are pivotally attached at their bases to the inside of a cylindrical insert which is installed between the base of the hydrant and the underlying standpipe or shoe. Various embodiments of the present backflow prevention valve provide for installation within both dry barrel and wet barrel type hydrants, with the cylindrical insert having a flanged fitting(s) for bolting between the hydrant components, or other conventional attachment as required. The present valve is completely automatic in its operation, opening as water flow through the hydrant and out the hydrant outlet(s) pushes it open, and automatically closing when the flow is shut off. Any frangible, breakaway couplings or components used with the original hydrant are retained when the present backflow prevention valve is installed. The present valve is not accessible without removing the hydrant from its base, thereby precluding tampering by unauthorized persons.  
      A discussion of the related art of which the present inventor is aware, and its differences and distinctions from the present invention, is provided below.  
      U.S. Pat. No. 3,185,171 issued on May 25, 1965 to Frank H. Mueller et al., titled “Valving Structure For Fire Hydrant,” describes a hydrant configuration having an easily replaceable seat assembly for the control valve in the base thereof. The Mueller et al. U.S. patent also discloses a frangible, breakaway control valve rod coupling and flanged hydrant attachment to provide for ease of replacement of the hydrant in the event that it is struck from its base (e.g., automobile collision, etc.). However, no backflow prevention valve, automated or otherwise, is disclosed by Mueller et al. in their patent.  
      U.S. Pat. No. 3,506,027 issued on Apr. 14, 1970 to John T. Dunton, titled “Fire Hydrant,” describes a “dry barrel” type hydrant having relatively small one way valves installed in the drain ports thereof. Dry barrel hydrants conventionally automatically drain the water from the barrel after use, to prevent freezing of any remaining water in the barrel and resultant damage to the hydrant barrel. The Dunton device comprises rubber flapper valves which are pushed closed due to water pressure in the upper portion of the hydrant, and which open when the water is shut off to allow water to drain from the upper barrel of the hydrant. No large capacity backflow prevention valve for flow from the hydrant supply and through the barrel is disclosed by Dunton.  
      U.S. Pat. No. 3,850,190 issued on Nov. 26, 1974 to Donald K. Carlson, titled “Backflow Preventer,” describes a flexible toroidal seal, the inner lip of which seals against a hemispherical shell in the center of the assembly. Fluid may flow in one direction through a series of peripheral ports around the central shell. The device is not adaptable for use in preventing backflow through the central barrel of a fire hydrant, as the flexible seal would not hold against significant backflow pressure in such a relatively large diameter installation. Moreover, the Carlson valve could not be installed in a fire hydrant to prevent backflow, as the central shell would preclude passage of the control valve stem therethrough in a wet barrel type hydrant. The Carlson valve also has outlets to release any backflowing fluid to the exterior of the valve, which would be unacceptable where a contaminated fluid of some sort is being introduced into the system.  
      U.S. Pat. No. 3,980,096 issued on Sep. 14, 1976 to Daniel A. Ellis et al., titled “Fire Hydrant,” describes a hydrant control valve configuration which allows the valve to remain with the hydrant shoe when the barrel is removed therefrom. No backflow prevention valve of any type is disclosed.  
      U.S. Pat. No. 3,980,097 issued on Sep. 14, 1976 to Daniel A. Ellis, titled “Fire Hydrant With Drain Valve And Backflow Preventer Mechanism,” describes the installation of small backflow prevention valves in the drain ports of a dry barrel type hydrant. These valves are much too small to serve as a backflow prevention valve for the main flow through the hydrant barrel, as provided by the present invention. In any event, the Ellis valves have no central clearance for a valve control shaft in a dry barrel type hydrant, as provided by at least one embodiment of the present invention.  
      U.S. Pat. No. 4,073,307 issued on Feb. 14, 1978 to John H. Royce, titled “Valve For Fire Hydrants,” describes a generally conventional control valve in which the resilient valve facing material includes a circumferential lip extension. Royce states that this provides a better seal when the valve is closed. However, no form of backflow prevention valve is disclosed by Royce.  
      U.S. Pat. No. 4,117,856 issued on Oct. 3, 1978 to Donald E. Carlson, titled “Frostproof Backflow Preventer,” describes a one way valve closely resembling the valve of the &#39;190 U.S. patent to the same inventor, discussed further above. The same differences noted between that device and the present invention are seen to apply here as well.  
      U.S. Pat. No. 4,139,931 issued on Feb. 20, 1979 to John H. Royce, titled “Assembly Method For Fire Hydrants,” is a division of the parent application upon which the issued &#39;307 U.S. patent (discussed further above) is based. The same differences noted above between the device of the &#39;307 U.S. patent and the present invention are seen to apply here as well.  
      U.S. Pat. No. 4,483,361 issued on Nov. 20, 1984 to Edward J. Jungbert, Sr., titled “Anti-Syphon Frost-Proof Hydrant,” describes a combination drain and anti-siphon valve located at the base of the assembly and extending from one side thereof, allowing water to flow from the barrel after the lower valve has been closed. However, the valve closes when pressure on the outlet side of the valve is higher than the pressure within the empty barrel. Due to the valve stems at each end of the device, it cannot be installed in a dry barrel type fire hydrant with a central control valve rod or stem. Moreover, the Jungbert, Sr. valve is not configured for use in relatively high pressure applications, whereas the present valve is constructed to handle relatively high pressure differentials and large flow volumes.  
      U.S. Pat. No. 4,763,686 issued on Aug. 16, 1988; U.S. Pat. No. 4,770,203 issued on Sep. 13, 1988; U.S. Pat. No. 4,790,341 issued on Dec. 13, 1988; and U.S. Pat. No. 4,791,952 issued on Dec. 20, 1988, all to David F. Laurel and titled “Hydrant And Components Thereof,” are a series of closely related patents describing numerous detail improvements in fire hydrants. None of the Laurel U.S. patents disclose any form of backflow prevention valve therein.  
      U.S. Pat. No. 5,129,416 issued on Jul. 14, 1992 to Rand H. Ackroyd, titled “Anti-Siphon Frost-Proof Water Hydrant,” describes a relatively complex water tap for outdoor installation, incorporating two backflow prevention valves and an air inlet. The two valves extend completely across the entire internal cross sectional area of the outlet, with no provision for any form of central control valve rod as is required in a dry barrel hydrant.  
      U.S. Pat. No. 5,228,470 issued on Jul. 20, 1993 to John E. Lair et al., titled “Self Draining Hose Connection Dual Check Valve Back Flow Preventer,” describes a very complex hose coupling multiple check valves therein. One of the valves has a flexible diaphragm with an opening around the stem of another valve. The two central valves are situated upon central stems, which preclude the use of this type of valve in a dry barrel type fire hydrant with its concentric valve control rod.  
      U.S. Pat. Nos. 5,590,679 and 5,632,303 issued respectively on Jan. 7 and May 27, 1997 to Lawrence Almasy et al., both titled “Wall Water Hydrant Having Backflow And Back Siphonage Preventor,” are continuations of the same abandoned parent patent application. Both describe a toroidally shaped, flexible elastic valve surrounding a central shaft. Water flow in the desired direction forces the outer edges of the valve to flex inwardly, toward the stem, with water flowing around the outside of the valve, rather than flowing through the center of the outwardly sealed valve as in the present invention. The Almasy et al. valve assemblies appear to be more closely related to the valve assembly of the &#39;470 Lair et al. U.S. patent, than to the present invention.  
      U.S. Pat. No. 5,971,022 issued on Oct. 26, 1999 to Bunya Hayashi et al., titled “Selector Valve With Counterflow Prevention Means,” describes a pneumatic or hydraulic multiple port valve with a plurality of concentric, one way seals. The seals open along their outer circumferences to allow flow, and flex outwardly to seal about their outer circumferences to block flow in the opposite direction. This configuration appears to be more closely related to the valves of the &#39;679 and &#39;303 U.S. patents to Almasy et al., described further above, than to the present invention.  
      U.S. Patent Publication No. 2002/144,731 published on Oct. 10, 2002, titled “Hydrant With Improved Drain Mechanism,” describes the installation of a diffuser(s) to the outlet(s) of the drain passage(s) in a dry barrel type fire hydrant. There is no backflow prevention valve provided with the diffuser, nor is any disclosed for the main water passageway of the hydrant.  
      U.S. Pat. No. 6,561,214 issued on May 13, 2003 to Howard Heil, titled “Hydrant With Improved Drain Mechanism,” is the issued patent based upon the &#39;731 U.S. patent application Publication to the same inventor, discussed immediately above. The same points noted in that discussion are seen to apply here as well.  
      Finally, Japanese Patent Publication No. 2002-21,123 published on Jan. 23, 2002, titled “Fire Hydrant,” describes (according to the drawings and English abstract) a single, side hinged flapper valve which is held in the closed position by a control rod which bears thereagainst. When the rod is raised, the valve is free to open to allow water to flow. Any back pressure when the valve is open, will push the valve back to its closed position against the seat to prevent backflow. The assembly serves as both the outlet flow control valve and backflow control valve, and would require replacement of the conventional valve in the base of the hydrant assembly for most U.S. hydrants. The outlet directly from the valve is also non-concentric, unlike U.S. hydrants, and cannot be readily adapted for use with U.S. hydrants.  
      None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. Thus a backflow prevention valve solving the aforementioned problems is desired.  
     SUMMARY OF THE INVENTION  
      The present backflow prevention valve comprises various embodiments which may be installed in either dry barrel or wet barrel type fire hydrants to prevent the unauthorized back flushing of the hydrant with a contaminated substance, thereby precluding the entrance of such a contaminated substance into the water supply. The present valve embodiments comprise generally cylindrical assemblies having a series of generally triangular segments or leaves pivotally attached to the inner peripheries thereof.  
      In an embodiment for dry barrel type hydrants, i.e., where the water is drained from the upper barrel when the control valve is closed, the backflow prevention valve segments seal against one another, with their apices sealing against the central control rod or stem for the underlying control valve. In an embodiment for a wet barrel type hydrant, i.e., where the water remains in the barrel due to the control valve being situated at the top of the barrel, the apices of the segments meet one another in the center of the barrel when the water is shut off.  
      The present backflow prevention valve body may include at least one externally disposed flange for bolting the device between the barrel and the underlying standpipe for the hydrant, with taller embodiments having opposed flanges at each end of the cylinder. A frangible coupling of the appropriate length is also provided for installation along the control rod in dry barrel hydrants, with the coupling also providing a bearing surface for the apex seals of the valve segments of the present invention.  
      These and other features of the present invention will become readily apparent upon consideration of the following specification and drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an environmental, elevation view of a first embodiment of a backflow prevention valve according to the present invention, installed in an otherwise conventional fire hydrant, riser, and shoe assembly.  
       FIG. 2  is an elevation view in section of the backflow prevention valve assembly of  FIG. 1 , showing the internal construction thereof.  
       FIG. 3  is a detailed broken away elevation view of the hinge detail of a single leaf or vane of the valve of  FIG. 2 , showing further details thereof.  
       FIG. 4  is an elevation view in section of a second embodiment of the present invention, configured for installation in wet barrel hydrants having no central control rod or stem.  
       FIG. 5  is a detailed perspective view of the attachment ring and leaves or segments of the present valve.  
       FIG. 6  is an elevation view in section of another embodiment of the present invention, in which the body comprises a single relatively thin ring. 
    
    
      Similar reference characters denote corresponding features consistently throughout the attached drawings.  
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The present invention comprises various embodiments of a completely automatic backflow prevention valve configured to withstand relatively high liquid backflow pressures, yet to allow relatively free liquid flow in the desired direction. It will be noted that the present valve may be incorporated in any of a number of different liquid conduits serving different purposes. However, a primary use of the present valve is envisioned with fire hydrants of various types and configurations, as illustrated in the drawing Figs.  
       FIG. 1  of the drawings illustrates a fire hydrant installation comprising a barrel B extending concentrically from a standpipe S. The hydrant assembly is conventional, with the exception of the installation of the present backflow prevention valve  10  sandwiched concentrically between the standpipe S and the barrel B. Conventionally, fire hydrant barrels B are secured to their underlying standpipes S by means of a mating circumferential barrel flange BF and standpipe flange SF and a series of peripheral bolts P passing therethrough. This greatly assists in protecting the underlying standpipe S from damage in the event the hydrant barrel B is damaged, e.g. struck by an automobile, etc., by allowing the barrel B to break away from the underlying structure without damage to that structure.  
       FIG. 2  illustrates further details of the present backflow prevention valve  10 . The valve  10  comprises a hollow cylindrical housing or body  12  having an open central area  14  defined by the inner periphery  16  of the housing  12 . The housing or body  12  has a first edge  18  and opposite second edge  20  which define a length or height  22  therebetween, with first and second attachment flanges  24  and  26  extending radially outwardly respectively from the first and second edges  18  and  20  of the housing  12 . The two flanges  24  and  26  of the housing or body  12  attach respectively to the standpipe flange SF and barrel flange BF by means of the peripheral bolts P. This places the hollow interior  14  of the housing or body  12  in a concentric relationship with the hollow barrel interior BI and standpipe interior SI, to allow liquid to flow freely through the assembly when the conventional lower shutoff or control valve (not shown) is opened.  
      The housing or body  12  contains a series of rigid, generally triangular valve segments therein, e.g. segments  28   a ,  28   b ,  28   c , etc., with  28   a  through  28   c  being shown in  FIG. 2 . Any practicable number of valve leaves or segments may be provided for the present invention, as desired. While the perspective view of an exemplary valve embodiment having six leaves or segments is illustrated in  FIG. 5  and discussed in detail further below, greater or fewer segments may be provided as desired. Each of the valve segments has a base, e.g. bases  30   a ,  30   b , and  30   c  shown in  FIG. 2 , a radially disposed first edge, e.g. first edges  32   a ,  32   b , and  32   c  in  FIG. 2 , a radially disposed second edge, e.g. second edges  34   a ,  34   b , and  34   c  in  FIG. 2 , and an apex, with truncated apices  36   a  and  36   c  being visible in  FIG. 2 . The first edges  32   a ,  32   b , etc. each mate with an adjacent second edge  34   a ,  34   b , etc. of an adjacent vane  28 , e.g. the first edge  32   a  of the first vane  28   a  mates with the second edge  34   b  of the second vane  28   b , the first edge  32   b  of the second vane  28   b  mates with the second edge  34   c  of the third vane  28   c , etc. around the circular configuration of the assembly. Various mating seals may be provided along these radially disposed edges, with an exemplary configuration being illustrated in  FIG. 5  and discussed further below.  
       FIG. 2  also shows the attachment of the various hinge segments  28   a ,  28   b , etc. within the housing or body  12 , with  FIG. 3  providing an exploded detail elevation view of this attachment. Each of the segments  28   a ,  28   b , etc. is connected at its base to a flexible hinge  38  which extends inwardly from the inner periphery  16  of the valve housing or body  12 . The hinge  38  may comprise a separate component for each valve segment  28   a ,  28   b , etc., or may comprise a toroidal configuration, with each of the valve segments  28   a ,  28   b , etc. being secured to an arcuate portion of the continuously circular flexible hinge  38 . The hinge  38  is formed of a resilient material having an outer peripheral valve housing attachment portion  40  and an opposite, inner peripheral valve segment attachment portion  42 . A clamp plate or ring  44  having a toroidal configuration seats within a recess  46  formed in the first or lower edge  18  of the housing or body  12 , and sandwiches the outer peripheral portion  40  of the flexible, resilient hinge  38  therebetween to secure the hinge  38  in place.  
      The hydrant configuration illustrated in  FIGS. 2 and 3  is that of a “dry barrel” hydrant, i.e. a hydrant having its shutoff or control valve disposed below the hydrant barrel B. When the control valve is opened, water flows upwardly through the valve and into the barrel, thence outwardly through the conventional hose fittings at the top of the barrel. When the control valve is closed, water drains from the barrel B by means of a few relatively small drain passages at the lower end of the barrel B. This prevents water from freezing within the barrel B and damaging the barrel B in below freezing temperatures. Accordingly, the housing or body  12  preferably includes a few such drain passages  48  disposed immediately above the valve assembly  28 , one of which is illustrated in  FIG. 3 , in order to allow water to drain from the barrel B.  
      As the conventional water shutoff or control valve employed with such dry barrel hydrants is located below the base of the barrel, a control valve rod or stem extends from the operating nut or fixture at the top of the hydrant, down through the interior of the hydrant to the shutoff valve. Such a configuration is shown in  FIG. 2  of the drawings. The control valve stem is conventionally formed in two lengths or segments joined by a frangible coupling, in order to preclude damage to the shutoff valve in the event the hydrant barrel B is knocked from its underlying standpipe S. Accordingly, the first and second control valve stem segments S 1  and S 2  pass concentrically through the standpipe S and barrel B, and are connected in the housing or body  12  by an elongated frangible coupling  50 . The coupling  50  is pinned at each end  52  and  54 , and includes a weakened, necked down portion  56  to allow breakage at that point  56  in the event the hydrant barrel B is dislodged from its standpipe S. The coupling  50  is of sufficient length to join the two valve stem segments S 1  and S 2  to compensate for the length or height  22  of the housing  12 , with the lengths of the housing  12  and coupling  50  being adjusted to correspond with one another as required.  
      In the above described dry barrel hydrant configuration, the apices  36   a ,  36   c , etc. bear against the outer circumference of the valve stem coupling  50 , rather than forming a sharp apex to seal against one another. Accordingly, the apices of the various valve segments  28   a , etc. are truncated for installation in such dry barrel type hydrants, with the truncated apices configured to fit closely against the side of the coupling  50  (or perhaps against the valve stem itself, depending upon the configuration of the assembly).  FIG. 3  of the drawings clearly shows such a truncated valve segment tip  36   a  for the valve segment  28   a , with the truncated tip  36   a  configured to fit closely against the circular shape of the coupling  50  of  FIG. 2 . It will be seen that some form of resilient seal may be provided to extend from the tip  36   a , as required. Such a resilient tip seal is shown in  FIG. 5  of the drawings, and discussed further below.  
      While dry barrel type hydrants are the most prevalent type in use, wet barrel hydrants, i.e. hydrants in which water remains in the upper barrel at all times, may also be found in certain locations. These hydrants have their water control valves situated at the top of the hydrant with water constantly filling the barrel of the hydrant, thus eliminating the need for a long control valve stem assembly. Accordingly, the truncated or relieved valve segment tip shown in  FIGS. 2 and 3 , is not required for such wet barrel type hydrants.  FIG. 4  illustrates a wet barrel hydrant embodiment of the present backflow prevention valve, designated as valve assembly  110 . The backflow prevention valve assembly  110  includes a housing or body  112  similar to the housing or body  10  of the dry barrel embodiment of  FIGS. 2 and 3 , but lacking the drain port(s)  48  of the dry barrel housing  12  shown in  FIG. 3 . The housing  112  includes an open central area  114  defined by an inner periphery  116 , and has opposed first and second edges or ends  118  and  120  defining a length or height  122 . First and second attachment flanges, respectively  124  and  126 , extend outwardly from the first and second ends  118  and  120 .  
      The valve body or housing  112  contains a series of generally triangular valve leaves or segments, respectively  128   a ,  128   b ,  128   c , etc., depending upon the number of segments of the valve assembly. Each segment is configured similarly to the valve segments  28   a ,  28   b , etc. of the assembly of  FIG. 2 , having a base edge  130   a ,  130   b , etc. pivotally extending from the inner periphery  116  of the valve body or housing  112 , and first and second radial edges, respectively  132   a ,  132   b , etc. and  134   a ,  134   b , etc. However, the extended point apices  136   a ,  136   b , etc. of the valve segments of the assembly of  FIG. 4  differ from the truncated apices  36   a ,  36   b , etc. of the assembly of  FIGS. 2 and 3 , as there is no central structure running concentrically through the hydrant and housing in a wet barrel type hydrant. Thus, the apices  136  am  136   b , etc. come to a relatively sharp point in such a wet barrel hydrant installation and bear against one another when the valve assembly is closed, rather than against a central shaft or coupling. The hinge  138  of the assembly  110  of  FIG. 4  may have the same configuration as that of the hinge  38  of the assembly  10  of  FIGS. 2 and 3 , i.e. a flexible, resilient toroidal having its outer edge secured between the first or lower edge of the housing or body  112  and a toroidal clamping plate or ring  144 . The valve leaves or segments  128   a ,  128   b , etc. are pivotally attached to the inboard portion of the hinge  138 , and flex upwardly and outwardly toward the inner wall or periphery  116  of the housing  112  when a liquid passes through the assembly from the standpipe S 2  to the hydrant barrel B 2 , just as in the case of the assembly of  FIGS. 2 and 3 .  
       FIG. 5  provides a perspective view of an exemplary valve segment assembly  210  for a dry barrel type hydrant, showing the sealing means used along the edges of the valve segments. It will be noted that rather than having a generally cylindrical housing, as in the embodiments of  FIGS. 1 through 4 , a relatively thin, toroidal ring  212  is provided from which the valve segments extend inwardly. The ring  212  includes an outwardly extending circumferential flange  224  to provide for attachment between the flanges of the standpipe and hydrant barrel, and an inner periphery  216 . A series of six generally triangular vanes  228   a  through  228   f  are pivotally secured by their bases  230   a  through  230   f  along the inner periphery  216  of the ring  212 . A flexible, resilient hinge member  238  with a toroidal configuration surrounds the segment bases  230   a  through  230   f , with the outer periphery  240  of the circumferential hinge  238  being secured to the flange  224  adjacent the inner periphery  216  of the ring  212 , and the inner periphery  242  folding upwardly and securing to the bases  230   a  through  230   f  of the valve segments or leaves  228   a  through  228   f.    
      Each of the valve segments  228   a  through  228   f  includes a first edge, respectively  232   a  through  232   f , an opposite second edge, respectively  234   a  through  234   f , and an apex, respectively  236   a  through  236   f . Each of the mating edges  232   a  through  232   f  and  234   a  through  234   f  includes means for sealing when the leaves or segments  228   a  through  228   f  are closed or folded together, generally as shown in  FIGS. 2, 4 , and  6 . Each of the first edges  232   a  through  232   f  includes parallel first and second lips, respectively  58  and  60 , which define a groove or channel  62  therebetween. The adjacent mating second edges  234   a  through  234   f  each have a convex ridge  64  extending therealong. When the valve leaves or segments  228   a  through  228   f  fold together when there is no flow through the hydrant, the ridges  64  of each of the segment first edges  232   a  through  232   f  nest within the corresponding groove or channel  62  between the lips  58  and  60  of the adjacent segment second edges  234   a  through  234   f , thereby providing a close seal between mating valve leaves or segments to preclude backflow of liquid therethrough.  
      The backflow prevention valve  210  of  FIG. 5  is configured for use in a dry barrel type hydrant, due to the truncated apices  236   a  through  236   f  of each of the valve segments  228   a  through  228   f . Additional apex seals  66  extend from each of the truncated apices, and bear against the central coupling  50  (shown in  FIG. 2 ) when the valve segments  228   a  through  228   f  are closed. These apex seals  66 , along with the edge sealing lips, grooves, and ridges  58  through  64 , provide a reasonably secure seal against backflow through the valve mechanism while still allowing the segments to hinge outwardly against the inner periphery of the backflow prevention valve housing or hydrant barrel, depending upon the valve embodiment employed.  
       FIG. 6  provides an elevation view in section of another backflow prevention valve assembly  310 , installed between a standpipe S and a hydrant barrel B, with the standpipe S and barrel B being essentially identical to the standpipe S and barrel B shown in  FIGS. 1 and 2 . The backflow prevention valve assembly  310  of  FIG. 6  is quite similar to the valve assembly  210  of  FIG. 5 , comprising a toroidal ring  312  with a circumferentially extending flange  324  which bolts between the flanges F of the standpipe S and hydrant barrel B and is secured in place by peripheral bolts P.  
      A series of valve segments or leaves extend from the inner periphery  316  of the ring  312 , with three of the segments  328   a  through  328   c  being shown in the cross sectional view of  FIG. 6 . The edge and apex seals may be essentially identical to those illustrated in  FIG. 5  of the drawings, and discussed further above. However, the flexible hinge  338  is configured differently, with its outer peripheral housing or ring attachment edge  340  extending downwardly along the inner periphery rather than being sandwiched between the circumference of the ring  312  and a circumferential retaining ring, as shown in  FIGS. 2 through 5  of the drawings. The inner circumferential portion or edge  342  of the hinge  338  secures to the bases  330   a  through  330   c  of the valve segments  328   a  through  328   e , as in the embodiments of  FIGS. 2 through 5 .  
      The above described arrangement may be used in either dry barrel or wet barrel type hydrants, with the primary difference being in the configuration of the apices of the valve segments. In  FIG. 6 , the truncated apices  336   a  and  336   c  are shown in solid lines, abutting the central coupling  350 . (The coupling need not be so long as shown in  FIG. 6  when a relatively thin ring valve configuration is used, but the longer length provides a smooth surface against which the apices of the valve segments may seal.) Where the valve assembly  310  is used in a wet barrel type hydrant without the central control valve stem components S 1  and S 2 , the apices are extended to form mating points, as shown by the apex portions  336   a  and  336   c  shown in broken lines in  FIG. 6 . The sealing means illustrated in  FIG. 5  and discussed further above may be incorporated along the edges of the valve segments of the embodiment  310  of  FIG. 6 , and other embodiments as well.  
      In conclusion, the present backflow prevention valve in its various embodiments provides a positive, fully automatic means of preventing liquid flow through a conduit in an undesired direction. The present valve may be used in sewage conduits to prevent backups, and/or various other fluid conduit systems as applicable. However, it may find its greatest value in fire hydrant installations, where it will prevent the unauthorized backflushing of hydrants with contaminants, as might otherwise be easily accomplished by terrorists. The present valve is well suited for installation in both dry and wet barrel hydrants, with the primary difference in the valve being the configuration of the valve segment apices to accommodate the central control valve stem in dry barrel hydrants or to mate with one another in wet barrel hydrants.  
      The present valve is relatively low, and extends the height of a hydrant by only a few inches so as not to exceed any maximum height standards. Where height is even more critical, the ring embodiments of  FIGS. 5 and 6  may be employed. While flanges have been illustrated with each of the various embodiments disclosed herein, it will be understood that other conventional means may be used for connecting the present backflow prevention valve with other components, e.g. mating threaded attachments as in pipe fittings, etc.  
      Any of a number of suitable materials may be used to construct the various components of the present valve embodiments. The outer housing or ring may be cast of iron, similarly to the technique conventionally used for forming fire hydrant barrels, standpipes, and similar components. The vanes must be a relatively stiff material, in order to resist the pressure developed by a high pressure pump in an attempt to induce backflow through the system. Various metals may be used, or alternatively relatively stiff plastics may be used, depending upon the diameter of the valve, the anticipated pressure, and perhaps other factors. The sealing edges and apices may be coated or fitted with relatively softer materials, e.g. Neoprene®, rubber, or other suitable material, in order to provide a water tight seal. Where dry barrel installations are made, the central coupling is preferably formed with a relatively low friction coating to allow the coupling to slide downwardly and upwardly between the apex seals as the operating valve is opened and closed.  
      Accordingly, the present backflow prevention valve will greatly reduce the risks of contamination to a water supply through a hydrant system, and will prove to be of great value and to greatly improve peace of mind for those responsible for municipal water systems.  
      It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.