Patent Publication Number: US-6659126-B2

Title: Backflow preventor with adjustable outflow direction

Description:
This is a continuation of application Ser. No. 09/566,771 filed May 8, 2000, which is a continuation of application Ser. No. 08/970,592 filed Nov. 14, 1997 (now abandoned), which is a continuation of application Ser. No. 08/613,015 filed Mar. 8, 1996 (now abandoned), which is a continuation of application Ser. No. 08/328,216 filed Oct. 25, 1994 (now U.S. Pat. No. 5,503,176), which is a continuation of application Ser. No. 08/046,337 filed Apr. 12, 1993 (now U.S. Pat. No. 5,385,166), which is a continuation of application Ser. No. 07/848,574 filed Mar. 9, 1992 (now U.S. Pat. No. 5,226,441), which is a continuation-in-part of application Ser. No. 07/650,799 filed Feb. 5, 1991 (now U.S. Pat. No. 5,107,888), which is a continuation-in-part of application Ser. No. 07/435,870 filed Nov. 13, 1989 (now U.S. Pat. No. 4,989,635), all of which are incorporated herein by reference in their entireties. 
    
    
     The present invention relates to a backflow preventor and, in particular, to a preventor with a provision for adjusting the outlet direction. 
     BACKGROUND OF THE INVENTION 
     Check valves are well known for use in assuring that a flow through a conduit occurs only in a predefined direction. Check valves are used, for example, in backflow prevention assemblies to prevent backflow of one fluid body into another. Back flow prevention is often used in connection with protecting potable water supplies from contaminants which could otherwise be introduced into it via back-siphonage or back-pressure. Many backflow preventors are designed to accommodate pressure commonly encountered in municipal water supplies, such as 150 psi (1030 kPa) or more. 
     Several factors are important in designing or selecting a backflow preventor for a particular use, including performance (e.g., minimizing pressure drop), serviceability, and ease and cost of installation. 
     Many backflow preventors are configured such that the direction of inlet and the direction of outlet flow are predetermined. In these devices, when it is desired to provide an outlet flow direction that is different (with respect to the inlet flow direction) from the predetermined direction, additional fittings such as elbows, U-joints, L-joints, T-joints and the like, must be connected. These additional fittings not only add to the cost of parts, labor and design involved in installing these devices, but also contribute to undesirable pressure loss. These additional fittings further take up volume and thus are impractical in applications having close clearances. Such pressure loss can be particularly troublesome in applications where maintenance of pressure is important such as in fire protection systems and high rise buildings. 
     In previous devices, maximizing serviceability has been incompatible with also maximizing the performance and installation factors. Thus, in past devices, efforts to increase the performance and ease of installation has produced devices with decreased serviceability. FIG. 6 depicts, schematically, a previous backflow preventor  110  which attempted to provide ease of serviceability by including both valves in  112   a ,  112   b  in a vertical configuration and a cover  114  which, when removed, permits access to the valves  112   a ,  112   b  (e.g., for maintenance purposes) in a vertical direction. The device shown in FIG. 6, however, provides a less than optimal performance. This is at least partially because, owing to the orientation of the valves  112   a ,  112   b  with respect to the inlet opening  116  and outlet opening  118  flow through the valve openings  116 ,  118  is forced to follow a divergent path (indicated by solid arrow streamlines  120   a ,  120   b ). The blocking action of the valve disks  122   a ,  122   b , causing this divergent flow  120   a ,  120   b , provides resistance to flow through the backflow preventor  110  and increases the pressure drop which the backflow preventor produces. 
     The device depicted in FIG. 6 also has deficiencies from the point of view of installation. In general terms, the cost of installation is least when the backflow preventor occupies the smallest amount of space. Thus, when a backflow preventor is installed in a building, it is desired to minimize the floor space required for installation. When the backflow preventor is installed outside a building, the expense of installation is related to the size of the enclosure required (e.g., enclosure  132  depicted in FIG.  7 ). When the backflow preventor is installed underground, it is desirable to minimize the size of the trench (not shown) required for underground installation. 
     As seen in FIG. 6, the inlet conduit and outlet conduit  124 ,  126  occupy a horizontal distance  128  which determines the minimum amount of space theoretically needed for installation of a backflow preventor. The upper portion  134  of the backflow preventor  110  occupies a horizontal extent  136  which is only slightly greater than theoretically minimum horizontal extent  128  required for installation. However, the lower portion  138  has a minimum horizontal extent  142  which is substantially greater, principally because the handle portions  144   a ,  144   b  of the shutoff valves extend outward from the housing  146  in a direction which is parallel to the axis of the conduits  124 ,  126  (i.e., parallel to a line passing through the conduits  124 ,  126 ). Moreover, an even larger horizontal expanse  148  is required to accommodate opening of the shutoff valves since the handles  144   a ,  144   b  move in a direction parallel to the axis of the conduits  124 ,  126 . 
     FIG. 7 depicts another configuration for a backflow preventor which also has certain deficiencies. The axes  152   a ,  152   b  along which the first and second check valves  154   a ,  154   b  extend (defined, for these purposes, as a line passing through the center of the inlet port of the valves  154   a ,  154   b  and parallel to the direction of flow into the valves) are parallel and both extend at an angle of about 45° to vertical. Access for maintenance is obtained by removing covers  156   a ,  156   b  to provide openings. The openings lie in planes  158   a ,  158   b  which are inclined to the horizontal by about 45°. Because neither of the openings lies in a horizontal plane, the device does not provide for access in a vertical direction. This represents a drawback to the serviceability of the device in FIG.  7 . 
     Installation of the device shown in FIG. 7 also has certain drawbacks. Installation requires certain additional parts such as 90° elbows  162   a ,  162   b  to change the flow direction from the upward and downward flow of the inlet and outlet conduits  124 ,  126  to the horizontal flow direction of a backflow preventor  164 . The size of the enclosure  132  required is relatively large to accommodate the extra parts  162   a ,  162   b  and since the two shutoff valves  166   a ,  166   b  and check valves  154   a ,  154   b  are generally linearly arrayed. Because of the change in flow direction, the flanges  168   a ,  168   b  for installing the backflow preventor  164  are vertically oriented. This requires provision of supports  172   a ,  172   b  for supporting and positioning the backflow preventor  164  at least during installation. As with the device depicted in FIG. 6, the check valves  154   a ,  154   b  of the device in FIG. 7 are of a type requiring that the flow through the valves be divergent  120   a ,  120   b  around the edges of the valve disks. 
     FIG. 8 depicts another type of previously-provided backflow preventor also having certain deficiencies. 
     The axes  152   c ,  152   d , along which the first and second check valves  154   a ,  154   b  extend, are perpendicular and both extend at an angle of 45° to vertical. Covers  156   c ,  156   d  cover access openings which lie in planes  158   c ,  158   d , neither of which lies in a horizontal plane. Additional parts such as elbows  162   c ,  162   d  are required for installation. The two shutoff valves  166   c ,  166   d  and the two check valves  154   c ,  154   d  are generally linearly arrayed. The means for connection  168   c ,  168   d  of the inlet and outlet of the stop valves  166   c ,  166   d  are vertically oriented. The check valves  154   c ,  154   d  are of a type requiring that the flow through the valves be divergent  120   a ,  120   b  around the edges of the valve disks. 
     Typically, a check valve is designed to maintain its open configuration as long as there is flow through the valve. Once the flow stops or drops below a predetermined value, the check valve closes. Typically, check valves are designed so that, once the valve is closed, the inlet pressure must exceed a predetermined threshold before the valve will open. Usually, a single structure, typically a spring, is used both to provide the force to hold the valve closed (until the threshold is reached), and to provide the biasing force which moves the valve from the opened to the closed position. Because the biasing device provides some force tending to close the valve, even during normal flow conditions, a countervailing force must be provided to counteract the closing force and maintain the valve open, during normal flow conditions. Typically, the countervailing force is provided by the fluid moving through the valve. Accordingly, as the pressurized fluid moves through the valve, some amount of work is expended in holding the valve in the open position in opposition to the biasing force tending to close the valve. This expenditure of work causes a pressure drop across the check valve, so that the check valve itself necessarily creates a certain amount of loss of the pressure head. The amount of pressure minimally required at the inlet in order to maintain the valve in the open position is termed the “hold-open pressure.” It is desirable to minimize the pressure drop or head loss during transit through the check valve, and, thus, it is desirable to reduce the hold-open force. Particularly, it is desirable that the hold-open force should be less than that from the threshold pressure. Accordingly, a number of previous check valves having a biasing device have been produced, which create a greater force on the valve when it is in the closed position than when in the open position. 
     Many previous designs for reduced hold-open pressure check valves involve providing a linkage of one or more rigid pivoting arms connecting the clapper to the wall or body of the valve. U.S. Pat. No. 980,188, issued Jan. 3, 1911, to Blauvelt, for example, discloses a flap or swing-type valve having a clapper which can pivot toward or away from a valve seat. The clapper is pivotally connected to a rigid link or arm which, in turn, is pivotally connected to a spring. 
     Other valving devices include a knuckle or toggle-type linkage having two or more relatively pivoting arms or links. 
     SUMMARY OF THE INVENTION 
     The present invention includes the recognition of problems in previous devices, including those described above. According to the present invention, a backflow preventor is provided which permits adjustment of the outflow direction with respect to the inflow direction, preferably among an infinite number of outlet flow directions. In one embodiment, adjustment is provided by making the portion of the housing which houses the second backflow preventor valve movable or rotatable with respect to the section of housing which houses the first backflow preventor valve. In one embodiment, a cylindrical region of the housing connects the two valves and this cylindrical region can be separated to permit rotation of a portion of the cylindrical housing region with respect to the other portion. In one embodiment, the cylindrical portion includes annular shouldered flats for accommodating a pipe coupling. In one embodiment, the housing is provided as a single casting which can be separated, between the flats, by sawing or otherwise cutting through the cylindrical portion of the housing. 
     It has been found that performance of backflow preventors is degraded when the number of changes in flow direction is increased. An increase in the number of changes in average streamline flow direction tends to increase pressure drop and degrade performance of a backflow preventor. As used herein, average streamlines can be considered to pass through the center of valve inlets, pass along a direction from an upstream valve outlet to a downstream valve inlet and pass along the centers of conduits elsewhere. Although the above-defined average streamline is used for purposes of explanation and analysis, it is recognized that actual flow will typically contain some amount of turbulence. Nevertheless, for purposes of explanation of the present invention, the defined and depicted streamlines approximate the general flow direction and are believed to approximate the actual streamlines averaged in space and time. 
     FIG. 7 depicts the average streamline  182  as dotted arrows. Tracing the flow from the upper flow in the inlet conduit  182  the downward flow in the outlet conduit  126 , there is a 90° change  184   a  at the first elbow joint  162   a , a 45° change  184   b  just prior to the inlet port of the first valve  154   a,  90° change  184   c  between the inlet and outlet of the first valve  154   a , a 45° change  184   d  downstream of the outlet of the first valve  154   a , a 45° change  184   e  upstream of the inlet to the second valve  154   b , a 90° change  184   f  between the inlet and the outlet of the second check valve  154   b , a 45° change  184   g  downstream of the outlet from the second check valve  154   b  and a 90° change  184   h  at the second elbow  162   b . Thus, average streamline analysis shows that there is a total of 540° of change between the inlet conduit  124  and the outlet conduit  126 . 
     FIG. 8 shows the average streamline  182  for the configuration depicted therein. There is a 90° change  186   a  at the first elbow joint  162   c , a 45° change  186   b  prior to the inlet part of the first valve  154   c , a 90° change  186   c  between the inlet and outlet of the first valve  154   c , a 90° change  186   d  between the inlet and outlet of the second check valve  154   d , a 45° change  186   e  downstream of the outlet from the second check valve  154   d , and a 90° change  186   f  at the second elbow  162   d . Thus, average streamline analysis shows that there is a total of 450° of change between the inlet conduit  124  and the outlet conduit  126 . 
     A corresponding streamline analysis of the device shown in FIG. 6 indicates a total flow change of about 180°. 
     The present invention provides for increased performance without unacceptably degrading serviceability or installation factors. The present invention provides for a flow through open valves without requiring the flow to diverge around the edges of the valve disks. The valve components of the present invention, rather than inhibiting flow by requiring divergence as the flow moves through the valves, tends to enhance the desired flow by directing flow along the desired path. The present invention has an average streamline flow change of direction totalling about 180°. According to an embodiment of the present invention access to one of the check valves is in a vertical direction while access to the other is in a horizontal direction. The valves preferably extend along axes which are oriented at 90° to one another. 
     Valves containing a relatively large number of moving parts, such as pivoting rigid arms, are typically susceptible to wear or deterioration, particularly in corrosive, contaminated, or depositional environments, such as in hard water. Furthermore, rigid linkage systems are relatively expensive to design, produce, install, and maintain. Installation and maintenance often require use of special tools. 
     The present invention includes a spring which connects the valve clapper to the valve body. Preferably the spring connects the clapper to a removable cover portion of the valve body. The spring can be viewed as taking the place of one or more of the rigid links of previous devices. Preferably, the spring is directly connected to the clapper device, i.e., without an intervening linkage, and forms the sole connection between the clapper device and the valve wall (preferably the cover portion of the valve wall). The spring pivots with respect to the clapper about a pivot point, with the pivot point remaining in a fixed position with respect to both the end of the spring and the clapper device during opening and closing of the valve. The spring provides a force along its longitudinal axis without a lateral component. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view through a check valving device showing a closed check valve and an opened check valve; 
     FIG. 1A is a partial cross-sectional view corresponding to FIG. 1, but showing another embodiment; 
     FIG. 2 is a cross-sectional view taken along line  2 — 2  of FIG. 1; and 
     FIGS. 3A and 3B depict, schematically, the triangles formed by the pivoting or attachment axes or points in the closed and opened configurations, respectively; 
     FIGS. 4A and 4B depict, schematically, an unstressed helical spring and a compressed and bowed helical spring; 
     FIGS. 5A and 5B depict, schematically, two end-joined helical springs, in unstressed and stressed configurations, respectively; 
     FIG. 6 is a schematic cross-sectional view of a backflow preventor according to a previous device; 
     FIG. 7 is a schematic cross-sectional view of an enclosed backflow preventor according to a previous device; 
     FIG. 8 is a schematic cross-sectional view of a backflow preventor according to a previous device; 
     FIG. 9 is a side elevational view, partly in cross-section, of a backflow preventor; 
     FIG. 10 is a side-elevational view of a backflow preventor; and 
     FIG. 11 is a side-elevational view of a backflow preventor; 
     FIG. 12 is a side-elevational view, partly in cross-section, of a backflow preventor, according to one embodiment of the present invention; 
     FIG. 13 is a side-elevational view of a backflow preventor, according to one embodiment of the present invention; 
     FIG. 14 is a cross-sectional view of portions of a backflow preventor housing coupled by a coupler according to one-embodiment of the present invention; 
     FIG. 15 is a cross-sectional view taken along line  15 — 15  of FIG. 14; 
     FIG. 16A is a schematic simplified view of the apparatus depicted in FIG. 13; 
     FIG. 16B is an end view of the apparatus of FIG. 16A; 
     FIG. 17A is a side-elevational view of the apparatus of FIG. 16A, but with the outlet flow direction changed by 90°; 
     FIG. 17B is an end view of the apparatus of FIG. 17A; 
     FIG. 18A is a side-elevational view of the apparatus of FIG. 16A, but with the outlet flow direction rotated by 180°; and 
     FIG. 18B is an end view of the apparatus of FIG.  18 A. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A backflow preventor  212 , according to one embodiment of the present invention, is depicted in FIG.  12 . The backflow preventor  212  includes first and second shutoff valves  214   a ,  214   b  and first and second check valves  12 ,  14 . Valves  214   a ,  214 ,  12 ,  14  are encased in a housing  216 . A conduit  228  provides fluid communication between the first check valve  12  and the second check valve  14 . The first and second check valves  12 ,  14  are positioned generally vertically above the inlet and outlet stop valves  218 ,  220  and the second check valve and shutoff valve  14 ,  214   b  are substantially level, but horizontally displaced from the first check valve and shutoff valve  12 ,  214   a . Thus, the flow from the first shutoff valve  214   a  to the first check valve  12  and the second check valve  14  and the second shutoff valve  214   b  is in a generally inverted U-shape, as opposed to a linear shape. 
     During the operation, fluid enters the first shutoff valve  14   a  from the inlet conduit  124  in a first flow direction  268 . When the flow reaches the first check valve  12  there is a 90° change of direction  274 . The flow  272   b  flows through the conduit  228  towards the second check valve  14 . When the flow  272   b  reaches the second check valve  14 , there is a second 90° change in flow direction  282  of the average streamline  272 . As can be seen from FIG. 12, the total change in direction of the average streamline  272  is the sum of the two changes of direction  274 ,  282 , both of which are approximately 90°, providing a total of about 180° of change in direction. In the configuration depicted in FIG. 12, the direction of outflow  272   c  is substantially parallel to, spaced from, and opposite in direction from the direction of inflow  272   a.    
     As depicted in FIG. 12, conduit  228  is provided with a device for permitting adjustment of the outflow direction. In the embodiment of FIG. 12, this device includes first and second spaced-apart annular flats  312 ,  314 . In external, as shown in FIG. 13, the annular flats  312 ,  314  appear as ribs or ridges spaced apart by a groove  316 . The outer faces  318 ,  320  of the flats  312 ,  314  are substantially cylindrical. The shoulders  322 ,  324  connecting the flats  312 ,  314  to the main portion of the conduit  228  are preferably slightly curved. In the embodiment of FIGS. 12 and 13 the conduit  228  and both flats  312  and  314  are integrally formed such as from a single casting. In this way, the backflow preventor of the present invention can be used in a first configuration with the inflow direction  272   a  and outflow direction  272   c  parallel and opposite, as shown in FIG. 12, or can be reconfigured to provide a different outflow direction. In order to provide such different outflow direction, the conduit  228  is cut such as by sawing along the groove  316 . Preferably, the kerf created by the cut will leave substantially flat faces. Such cutting divides the conduit  228  into a first portion  326  and a second portion  328 . After cutting, the first and second portions  326 ,  328  are separated. The second portion  328  can now be moved, such as by being rotated, with respect to the first portion  326 , as described more fully below. After rotating, the first portion and second portion  326 ,  328  are connected, such as by using a coupling device  330  such as that depicted in FIGS. 14 and 15. The coupling  330  depicted in FIGS. 14 and 15 includes a gasket, such as a rubber gasket  332 , a key  334  and a housing  336 . The gasket  332  may be substantially annular in shape. Preferably, the key  334  and housing  336  are of a split-ring type which can be drawn and held together by a connector such as bolts  338  and nuts  340 . The key  334  includes ledges  342 ,  344  which engage the shoulders  322 ,  324  of the flats  312 ,  314 . The coupler  330  is configured to provide a leak-free connection between the first and second portions  326 ,  328  of the conduit  228 . 
     As depicted in FIG. 16A, when the conduit  228  is uncut, the inlet flow direction  272   a  and outlet flow direction  272   c , respectively defined by the valve inlet opening  350  and outlet opening  352  are substantially parallel and opposite. After the conduit  228  is cut, as described above, the valve can be reconfigured to provide a different outflow direction. For example, as depicted in FIG. 17A, the right hand portion of the conduit  228  can be rotated to an angle  354  of about 90° to provide an outlet opening  352  defining an outflow direction  272   d  which is different from the first outflow direction  272   c . In the configuration depicted in FIGS. 17A and 17B, the outflow direction  272   d  is substantially at right angles to the inflow direction  272   a . Because the outlet opening  352  can be placed in a plurality of different positions, by rotating different angles, a plurality of outflow directions, preferably an infinite number of outflow directions, can be provided. In the depicted embodiment, all of the outflow directions lie in a plane parallel to the inflow direction  272   a . In the configuration depicted in FIGS. 18A and 18B, the outflow opening  352  has been rotated through an angle  356  of about 180° to provide an outflow direction  272   e  which is parallel to and in the same direction as the inflow direction  272   a.    
     A backflow preventor  212  is depicted in FIG.  9 . The backflow preventor  212  includes first and second shutoff valves  214   a ,  214   b  and first and second check valves  12 ,  14 . The shutoff valves can be any of a number of well-known valve designs, including a ball valve, a gate valve, or, preferably, a globe valve. Preferably, the shutoff valves can be manually opened or closed by moving external handles  269   a ,  296   b . The valves  214   a ,  214   b ,  12 ,  14  are encased in a housing  216  which includes an inlet lower portion  218 , a valve body  16 , and an outlet lower portion  220 . A conduit  222  leads from the first shutoff valve  214   a  to the inlet port  224  of the first check valve  12 . The inlet port  224  is preferably circular in shape and surrounded by a valve seat  28 . The inlet port  224  can be closed by the clapper or valve disk  32 . The valve disk  32  is movable between a closed configuration or position (FIG. 1) and an open configuration as depicted in FIG.  9 . The flow exits the first valve region  12  through an outlet port  226  and enters a conduit  228  which provides fluid communication between the first check valve  12  and the second check valve  14 . In the embodiment depicted in FIG. 9, the conduit  228  contains a first downward sloping portion  232  imparting a shape to the apparatus similar to the letter “N”. At the downstream end of the conduit  228  is an inlet port  234  of the second check valve  14 . Surrounding the inlet port  234  is a valve seat  76 . The second check valve  14  operates in a manner substantially similar to that of the first check valve  12  as described more fully below. Flow leaves the second check valve  14  to an outlet port  236  and is conveyed by a conduit  238  to a second shutoff valve  214   b.    
     As seen in FIG. 9, the first and second check valves  12 ,  14  are positioned generally vertically above the inlet and outlet stop valves  218 ,  220  and the second check valve and shutoff valve  14 ,  214   b  are substantially level, but horizontally displaced from the first check valve and shutoff valve  12 ,  214   a . Thus, the flow from the first shutoff valve  214   a  to the first check valve  12 , the second check valve  12  and the second shutoff valve  214   b  is in a generally inverted-U shaped, as opposed to a linear shape such as that depicted in FIGS. 7 and 8. In this way, the horizontal extent  262  of the backflow preventor  212  is reduced, compared to linear configurations such as those in FIGS. 7 and 8. As can be seen from FIG. 9, the horizontal extent  262  of the backflow preventor  212  is also reduced, compared to a configuration such as that depicted in FIG. 6, since the handles  264   a ,  264   b  by which the shutoff valves  214   a ,  214   b  are operated, extend in a direction perpendicular to a line connecting the inlet and outlet conduits  124 ,  126 . The direction in which the handles  264   a ,  264   b  move as the shutoff valves  214   a ,  214   b  are opened and closed, is a direction perpendicular to a line connecting the conduits  124 ,  126 . By providing shutoff valve handles  264   a ,  264   b  which extend and move in a direction perpendicular to the line connecting the conduits  124 ,  126 , the horizontal extent of the backflow preventor  212 , in a direction along the line connecting the conduits  124 ,  126  is reduced, compared to devices such as that depicted in FIG.  6 . 
     The first check valve  12  extends generally along an axis  242 . The second check valve  14  extends along an axis  244 . In the embodiment depicted in FIG. 9, the second check valve extends along an axis  244  which is at approximately 90° to the axis  242  of the first check valve  12 . 
     An opening  246  is provided in the housing  216  in the region of the first check valve  12 , covered by a covering  248 . The covering  248  (FIG. 10) is removably held in place by bolts  252   a ,  252   b . When access to the first check valve  12  is desired, such as for maintenance or installation, the bolts  258   a ,  258   b  are removed and the covering  248  is removed to expose the first check valve  12  through the opening  246 . As can be seen from FIG. 9, access to the first check valve  12  is along a vertical direction. 
     A second opening  254  is provided in the housing  216  in the region of the second check valve  14 . The opening  254  is covered by a covering  256  removably held in place by bolts  258   a ,  258   b . When access to the second check valve  14  is desired, the covering  256  is removed. As can be seen from FIG. 9, access to the second check valve  214  is in a horizontal direction. 
     The lower portion of the backflow preventor  212  includes flanges  266   a ,  266   b  for connection to the inlet and outlet conduits  124 ,  126 . Because the flanges  266   a ,  266   b  are horizontally oriented, the backflow preventor  212  can be positioned to rest on the inlet and outlet conduits  124 ,  126  during installation, thus avoiding the need for supports such as those  172   a ,  172   b  depicted in FIG.  7 . 
     During operation, fluid enters the first shutoff valve  214   a  from the inlet conduit  124  in a first flow direction  268 . The average streamline flow  272   a  continues through the conduit  222  and through the inlet port  224  without substantial change in direction until it reaches the valve disk or clapper  32 . As shown in FIG. 9, because of the configuration of the valve disk  32  flows through the inlet port  224  is substantially straight  276  and non-divergent. When the flow reaches the clapper  32  (i.e., when any fluid “parcel” component of the flow reaches the clapper  32 ) there is a 90° change of direction  274 . When the clapper  32  is in the open configuration, as depicted in FIG. 9, it is positioned so as to direct the flow (as analyzed by the position of the average streamline) from the first direction  272   a  (i.e., substantially vertically upward) to a second direction,  272   b  (i.e., substantially horizontally toward the second check valve  13 ). In the embodiment depicted in FIG. 9, the clapper  32  acts as a flow director because it forms a surface positioned substantially at an angle with respect to the upward flow  272   a.    
     The flow  272   b  which has been redirected by the clapper  32  exits the outlet port  226  and flows through the conduit  228  towards the second check valve  14 . The flow  272   b  passes through the inlet port  234  of the second check valve  14 . During such passage, the flow is substantially straight and non-divergent  278 . The flow  272   b  proceeds from the first check valve  12  to the second check valve  14  substantially without change of direction until it reaches the clapper  72  of the second check valve  14 . The clapper  72  acts as a flow director, in a manner similar to that of the first clapper  32 , redirecting the flow  272   b  to a vertically downward direction to  272   c . Thus, there is a second 90° change in flow direction  282  of the average streamline  272 . As can be seen from FIG. 9, the total change in direction of the average streamline  272  is the sum of the two changes of direction  274 ,  282 , both of which are approximately 90°, providing a total of about 180° of change in direction. 
     FIG. 11 depicts a backflow preventor  286 . The backflow preventor  286  depicted in FIG. 11 is substantially similar to the backflow preventor depicted in FIG. 10 except for the addition of a relief valve  288  and a conduit  292 . The relief valve  288  is provided in order to discharge possibly contaminated water into the atmosphere to prevent its entering the water source. A number of relief valves of types well-known in the art can be used. The relief valve  288  and conduit  292  are connected to the housing  216  in two places. The conduit  292  connects the relief valve  288  to a portion of the housing  293  which is upstream of the first check valve  12 . The relief valve  288  is also connected to a region  296  (FIG. 9) which is downstream of the first check valve  12 . For proper operation, the region  296  should be a distance  298  below the level  299  of the inlet port  224  for the first check valve  12 . This change in level  298  is provided by the downward sloping portion  232 . In operation, when pressure at the upstream location  293  falls below a predetermined level with respect to pressure in the valve interior, the valve  288  opens to permit discharge of water. 
     Test cocks  297   a ,  297   b ,  297   c  are connected to the housing  216  in order to provide a position for pressure testing, e.g., by connecting a differential pressure gauge. 
     As depicted in FIG. 1, a check valving device  10  is provided having a first check valve  12  and a second check valve  14 . A number of valves can be used for the check valves, including those depicted in FIGS. 1 and 2. When pivoting valves are used, such as the valves depicted in FIGS. 1 and 2, it is anticipated such valve with experience least wear when configured in the vertical up or vertical down positions (with horizontal pivot axes). Thus, when it is desired to avoid wear, the preferred configurations for the adjustable outlet, using such valves, will be those depicted in FIGS. 16A and 18A. If other orientations are desired, and wear is to be avoided, it would be preferable to mount the valves within the housing in a position such that, after adjusting outlet direction, the valve orientation will be vertically upward or downward. Alternatively, it may be possible to use another type of valve which is less susceptible to wear in other positions. Although FIG. 1 depicts the first check valve  12  in a closed position, and the second check valve  14  in an open position, in actual operation, as described more fully below, the first and second valves  12 ,  14  will open and close substantially simultaneously or within a short time interval of one another. The valving device includes a valve body  16  made up of a wall  18 . The valve body  16  can be formed of a number of materials, including ductile iron, brass, stainless, steel, or other metals, plastic, resin, glass, and/or ceramic and the like. The valve body  16  defines an inlet port  22  and an outlet port  24 , preferably having a substantially circular cross-section. Preferably, the inlet port and outlet port include devices, such as flanges  26 , for connecting the valving device  10  to fluid conduits. Adjacent to the inlet port  22  is a valve seat  28 , such as an annular seat formed, for example, of iron. 
     A disk-shaped clapper  32  is rigidly connected, such as by using a bolt  34  and nut  36 , to a clapper arm  38 . A first end  39  of the arm  38  is pivotally mounted adjacent the valve seat  28  by connection to a portion of the valve body  16  by a pivot joint  42   a ,  42   b  to permit pivoting of the arm  38 , and rigidly attached to disk  32  about a first axis  43 . 
     The lower surface of the clapper  32  includes a seat disk  44  configured to sealingly mate with the valve seat  28  when the clapper  32  is pivoted to its closed position, as depicted in the left portion of FIG.  1 . The disk  44  can be made of a number of materials, including plastic, rubber, resin, and the like, and is preferably a soft (such as about 40 durometer) elastomer material, such as a synthetic rubber e.g., EPDM (ethylene-propylene terpolymer). The disk  44  is reversible so that after it experiences wear, it can be removed, rotated 180° about a horizontal plane, and reinstalled. 
     The second end  48  of the clapper arm  38  is pivotally connected to a spring  52 . The spring  52  is contained between first and second spring seats  54 ,  56 . The spring  52  is preferably a helical spring which is compressional, i.e., is reduced in length as the valve  12  opens. The spring  52  can be formed of a number of materials, such as spring steel, plastic, or rubber. A single helical spring  52 ′, such as that depicted in FIG. 4A, is commonly subject to deformation when compressed. As shown in FIG. 4B, a compressed helical spring commonly assumes a bowed or arcuate configuration. Although such a spring can be used in accordance with the present invention, according to the preferred embodiment, two springs  52 A,  52 B are joined end-to-end by connection to a plate-like or annular device, such as a washer  53 , as depicted in FIG.  5 A. Upon compression, as depicted in FIG. 5B, such a spring  52  tends to maintain its linear configuration and is not subject to bowing or distortion to the degree an ordinary helical spring  52 B is. 
     The first spring seat  54  is pivotally attached to the second end  48  of the clapper arm  38  to permit pivoting of the spring  52  about a second axis  64 . 
     The second spring seat  56  is pivotally connected to the valve body wall  18 . In the preferred embodiment, the portion of the valve wall which the second spring seat  56  connects to is a removable cover  65  which can be attached to the remainder of the valve body wall  18 , by e.g., bolts, screws, clamps, or the like (not shown). As shown in FIG. 1, the second spring seat  56  can be connected within a pocket  58  at an attachment point  62 , to permit pivotal movement of the spring  52  about a third axis  66 . 
     In the embodiment depicted in FIG. 1, the second valve  14  is positioned downstream from the first valve  12 . Preferably, the second valve  14  is identical in construction to the first valve  12 , and includes a clapper  72 , a biasing device, such as a spring  74 , and a valve seat  76 . It will be understood, however, that the present invention can be used in single check valve configurations or other types of valve configurations. 
     Viewed in cross-section, each of the two valves  12 ,  14  define a triangle having vertices at the first axis  43 ,  43 ′, second axis  64 ,  64 ′, and third axis  66 ,  66 ′, respectfully. When the valve  12  is closed, the spring biasing device  52  provides a force to the clapper  32 , tending to hold the clapper  32  in the closed position. The amount of force is dependent upon two factors: (1) the magnitude of the longitudinal force provided by the spring  52 ; and (2) the component of that force which acts in a direction tending to close the clapper  32 . As depicted in FIGS. 3A and 3B, the spring closing force can be described as 
     
       
         Sin(180°−α).{overscore (F)}  (1) 
       
     
     where α  77 ,  77  ′ is the angle formed between the lines containing the first and second axes  43 ,  64 , and the line containing the second and third axes  64 ,  66 , and {overscore (F)}  79 ,  79 ′ is the vector force provided by the spring along the longitudinal spring axis which intersects the second axis  64  and third axis  66 . 
     When the inlet pressure exceeds the outlet pressure, an opening force is created. When the opening force on the clapper  32  exceeds the spring closing force (shown in equation (1)) plus any closing forces provided by other sources, such as fluid pressure the clapper  32  moves away from the valve seat  28 , opening the valve  12  to provide fluid communication between the inlet port and the outlet port  24 . During the opening movement of the valve  12 , the position of the second axis  64  changes with respect to the valve body  10 , but does not change with respect to the clapper  32  or with respect to the adjacent end of the spring  52 . 
     As the clapper  32  pivots about the first axis  43 , the angle α increases from a value of about 118°  77  in the configuration shown on the left-hand portion of FIG. 1 (depicted schematically in FIG. 3A) to a value of about 164°  77 ′ when in the fully opened configuration of the valve  14 , shown on the right-hand portion of FIG. 1 (depicted schematically in FIG.  3 B). The magnitude of the closing force provided to the clapper  32  thus changes from about 87% of that of the spring force {overscore (F)}  79  to about 27% of that of the spring force {overscore (F)}  79 ′. However, during this time, the magnitude of spring force {overscore (F)} also changes, since it is proportional to the length of the spring  52 , becoming larger as the valve  12  opens. In order to produce a valve  12  having a reduced hold-open force, the extreme values of the angle α  77 ,  77 ′, the distance between the first and third axes  43 ,  66 , and first and second axes  43 ,  64  are selected so that equation (1) yields a smaller closing force in the opened position of the valve (FIG. 3B) than in the closed position of the valve (FIG.  3 A). 
     The particular values for the hold-open force, maximum tolerable head loss, and the threshold opening pressure will depend upon the particular use or application of the valving device  10 . In one embodiment of the present invention, valving device  10  opens when the inlet pressure exceeds the outlet pressure by about 2-5 psi (about 14-35 kPa), and closes when the outlet pressure equals or exceeds the inlet pressure. Preferably, this embodiment has a head loss of less than 2 psi in a static or no-flow (limiting) condition, and there is little increase in head loss as the flow increases, such as a head loss of about 3 psi (about 20 kPa), with an operational flow velocity of about 7.5 ft./sec. (about 2.3 meters/sec.), or a rated flow velocity, e.g., 18 ft./sec. (about 5.5 meters/sec.) In another embodiment, the static condition head loss is about 8 psi (about 56 kPa), and the head loss during flow conditions remains below about 10 psi (about 70 kPa). 
     Based on the above description, a number of advantages of the present invention are apparent. The backflow preventer in the present invention has enhanced performance, such as lower pressure drop, and has a decreased number of changes of flow direction. By providing a device in which the valves are aligned 90° to each other and in which the total change of direction is about 180° , a backflow preventer is provided which has enhanced performance without substantial degradation of serviceability. 
     By using the apparatus of the present invention, a backflow preventor can be provided which provides outflow in any of a plurality of directions without the pressure loss and expense of providing additional fittings. For example, it is possible to provide inflow and outflow which are both directed vertically upward while reducing pressure loss in pressure-sensitive applications such as fire protection and high rise buildings. By providing a housing which can be cast as a unitary piece and, if desired, cut, the same body casting can be used, uncut in a standard device, as is used in the adjustable outlet when cut. 
     A number of modifications and variations of the invention can be used. The backflow preventor described above, in particular the housing and flow configuration, can be used in conjunction with check valves other than the check valves described, such as flapper valves with other types of biasing mechanisms. The check valve of the present invention can be used in combination with other valves or fluid-control devices. The valve can be used with fluids other than liquids. The valve can be configured without using a clapper arm, such as by directly pivoting the spring to the clapper and/or directly pivoting the clapper adjacent the valve seat. Other shapes and geometries of the clapper, ports, valve seats, and other components can be used. Other types of biasing devices can be used, including springs other than helical springs, hydraulic biasing devices, and the like. The present invention can be used employing other types of couplers for joining the separated portions of the conduit than those described and can be constructed of a variety of materials. The present invention can provide for movement of the outlet opening using devices other than the annular flats, such as by using a rotatable sealed joint. Although in one embodiment the housing is provided as a unitary piece which can be cut to achieve a rotation, the housing can also be provided in two or more separate pieces, e.g., joined by a coupling, so that it is not necessary to cut the housing in order to perform rotation. 
     Although the description of the invention has included a description of a preferred embodiment and certain modifications and variations, other modifications and variations can also be used, within the scope of the invention, which are described by the following claims.