Abstract:
A backflow preventer that includes a housing having an inlet and an outlet adapted to be mounted in a liquid flow configuration in a liquid supply circuit. An upstream check disc assembly is positioned in the housing downstream of the inlet, and includes an upstream check plate supporting a downstream diaphragm. An upstream check disc is positioned downstream of the diaphragm and integrally formed with an upstream stem mounted in an aperture in a central hub formed in the check plate for movement between a normally open, flow position and a closed position preventing backflow of liquid through the inlet. A downstream check disc assembly is positioned in the housing downstream from the upstream check disc assembly. A vent discharges liquid to atmosphere upstream of the downstream check disc assembly.

Description:
TECHNICAL FIELD AND BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to a dual check backflow preventer designed to protect liquid supply lines from back-siphonage or back-pressure of non-potable liquids. Backflow preventers of this type have two independently acting and spring-loaded check valves constructed of a corrosion resistant material. Such devices also typically have an intermediate atmospheric vent to insure protection from backflow conditions. The backflow preventer of this application is described with reference to its use in a water supply circuit, which is a principal usage. However, it will be understood that the subject matter of this invention is not limited to use with water, but is applicable to any liquid circuit where backflow is not desirable or permitted. 
         [0002]    During normal flow operation, the vent valve is closed, and the two check valves, which are in a flow series configuration, are open, allowing water to flow through the unit in a single direction. Each check valve is designed to hold a specified pressure in the direction of flow. When a backflow condition occurs, both check valves close and the atmospheric vent opens to permit air to enter the intermediate zone where the vent is located. In the event of back pressure, and if the second check valve is prevented from closing tightly, leakage is vented to atmosphere through the vent port. 
         [0003]    Backflow preventers are subject to harsh use conditions, including wide temperature and water pressure variations, but are expected nevertheless to operate flawlessly over long periods of time, both during normal use conditions and when back-siphoning occurs. The relatively large number of components inherently provides potential leak paths, particularly around rubber seals, the diaphragm and swaged areas. In addition, a properly designed and operating backflow In accordance with another embodiment of the invention, preventer should permit full flow during normal operation with a minimum of flow turbulence. 
         [0004]    Prior art backflow preventers include designs that are subject to premature wear and failure, leakage and flow-retarding turbulence. The present invention includes several novel features that correct these deficiencies. 
       SUMMARY OF THE INVENTION 
       [0005]    It is therefore an object of the present invention to provide a backflow preventer that reduces flow turbulence during normal operation. 
         [0006]    It is another object of the invention to provide a backflow preventer that includes an improved diaphragm with enhanced stress against rupture. 
         [0007]    It is another object of the invention to provide a backflow preventer that includes improved tolerances and sealing characteristics between and among components. 
         [0008]    It is another object of the invention to provide a backflow preventer that includes a check plate adapted to reduce exposed areas of the diaphragm, improve flow capacity and head pressure loss. 
         [0009]    These and other objects and advantages of the invention are achieved by providing a backflow preventer that includes a housing having an inlet and an outlet, and adapted to be mounted in a liquid flow configuration in a liquid circuit and an upstream check disc assembly positioned in the housing downstream of the inlet, and including an upstream check plate supporting a diaphragm positioned downstream thereof. An upstream check disc is positioned downstream of the diaphragm and is integrally formed with a stem extending upstream thereof and mounted in an aperture in a central hub formed in the check plate for movement between an normally open, flow position and a closed position preventing backflow of liquid through the inlet. A downstream check disc assembly is positioned in the housing downstream from the upstream check disc assembly, and a vent is provided from the housing upstream of the downstream check disc assembly and downstream of the upstream check disc assembly to atmosphere. 
         [0010]    In accordance with another embodiment of the invention, the upstream check plate includes a plurality of closely-spaced apart flow ports therethrough extending around the periphery thereof, and a plurality of radially-inwardly positioned flow ports surrounding the central hub of the upstream check plate. 
         [0011]    In accordance with another embodiment of the invention, the downstream check disc assembly includes a downstream check disc integrally formed with a stem extending upstream thereof and mounted in an aperture in a central hub formed in a flow opening in a wall of the housing for movement between an normally open, flow position and a closed position preventing backflow of liquid through the outlet. 
         [0012]    In accordance with another embodiment of the invention, a downstream facing face of the upstream check disc and the downstream facing face of the downstream check disc are convex. 
         [0013]    In accordance with another embodiment of the invention, a check seat disc is positioned against an upstream side of the upstream check disc and a support washer is positioned against an upstream of the downstream check disc. 
         [0014]    In accordance with another embodiment of the invention, the check seat disc positioned against the upstream side of the upstream check disc is fabricated of an elastomeric material and is adapted to seal against liquid flow when in the closed position against the diaphragm. 
         [0015]    In accordance with another embodiment of the invention, the support washer positioned against the upstream side of the downstream check disc is fabricated of an elastomeric material and is adapted to seal against liquid flow when in the closed position against the flow opening in the wall of the housing. 
         [0016]    In accordance with another embodiment of the invention, a diaphragm support ring is positioned in the housing downstream of and sealing against an annular rib formed in a downstream side of the diaphragm in both the open, flow and closed positions. 
         [0017]    In accordance with another embodiment of the invention, the downstream check disc assembly includes a check disc integrally formed with a stem extending upstream thereof and mounted in an aperture in a central hub formed in a flow opening in a wall of the housing for movement between an normally open, flow position and a closed position preventing backflow of liquid through the outlet. The downstream check disc assembly includes a check disc integrally formed with a stem extending upstream thereof and mounted in an aperture in a central hub formed in a flow opening in a wall of the housing for movement between an normally open, flow position and a closed position preventing backflow of liquid through the outlet. 
         [0018]    In accordance with another embodiment of the invention, the check plate is adapted to support the diaphragm on an upstream side thereof, and includes an outer, annular face engaging the diaphragm and an outer plurality of flow ports for allowing liquid to pass through the check plate and downstream around a centrally-formed opening in the diaphragm. A central opening in the check plate includes an integrally-formed hub positioned in the central opening in the check plate. A plurality of spokes extends radially outwardly from the hub and defines a plurality of voids for allowing liquid to pass through the check plate and downstream around a centrally-formed opening in the diaphragm. 
         [0019]    In accordance with another embodiment of the invention, a backflow preventer is provided that includes a housing having an inlet and an outlet, and that is adapted to be mounted in a liquid flow configuration in a liquid supply circuit. An upstream check disc assembly is positioned in the housing downstream of the inlet, and includes an upstream check plate supporting a diaphragm positioned downstream thereof. The upstream check plate is adapted to support the diaphragm on an upstream side thereof, and includes an outer, annular face engaging the diaphragm, an outer plurality of flow ports for allowing liquid to pass through the check plate and downstream around a centrally-formed opening in the diaphragm, a central opening in the check plate, an integrally-formed hub positioned in the central opening in the check plate, and a plurality of spokes extending radially outwardly from the hub and defining a plurality of voids for allowing liquid to pass through the check plate and downstream around a centrally-formed opening in the diaphragm. An upstream check disc is positioned downstream of the diaphragm and integrally formed with a stem extending upstream thereof and mounted in an aperture in the hub formed in the check plate for movement between an normally open, flow position and a closed position preventing backflow of liquid through the inlet. A downstream check disc assembly is positioned in the housing downstream from the upstream check disc assembly, and includes a downstream check disc integrally formed with a stem extending upstream thereof and mounted in an aperture in a central hub formed in a flow opening in a wall of the housing for movement between an normally open, flow position and a closed position preventing backflow of liquid through the outlet. A vent is provided from the housing upstream of the downstream check disc assembly and downstream of the upstream check disc assembly to atmosphere. 
         [0020]    In accordance with another embodiment of the invention, a diaphragm support ring is positioned in the housing downstream of and sealing against an annular rib formed in a downstream side of the diaphragm in both the open, flow and closed positions. 
         [0021]    In accordance with another embodiment of the invention, the upstream check disc and the downstream check disc are each spring-biased in normally closed position and adapted to be held open by a normal flow condition through the backflow preventer. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         [0022]    The present invention is best understood when the following detailed description of the invention is read with reference to the accompanying drawings, in which: 
           [0023]      FIG. 1  is a vertical longitudinal cross section of a prior art backflow preventer in an open flow condition; 
           [0024]      FIG. 2  is a vertical longitudinal cross section of an improved backflow preventer in a no flow condition according to a preferred embodiment of the invention; 
           [0025]      FIG. 3  is a vertical longitudinal cross section of an improved backflow preventer according to a preferred embodiment of the invention showing an improved, less turbulent flow path through the backflow preventer; 
           [0026]      FIG. 4  is a vertical longitudinal cross section of the backflow preventer of  FIGS. 2 and 3  showing a backflow-preventing flow path; 
           [0027]      FIG. 5  is an exploded perspective view of the backflow preventer shown in  FIGS. 2, 3  and  4 ; 
           [0028]      FIG. 6  is a perspective view of the upstream side of the upstream check plate assembly of the backflow preventer according to a preferred embodiment of the invention; 
           [0029]      FIG. 7  is a perspective view of the downstream side of the upstream check plate assembly of the backflow preventer according to a preferred embodiment of the invention; 
           [0030]      FIG. 8  is an exploded perspective view of the upstream check plate assembly of the backflow preventer according to a preferred embodiment of the invention; 
           [0031]      FIG. 9  is a vertical cross-section of the upstream check plate assembly of the backflow preventer according to a preferred embodiment of the invention; and 
           [0032]      FIG. 10  is an end elevation of the backflow housing. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Prior Art 
       [0033]    Referring now to  FIG. 1 , a prior art backflow preventer is shown at reference numeral  1 . Broadly described, the backflow preventer  1  includes a housing  2  attached to an inlet  3  and outlet  4 . An upstream check disc assembly  5  and downstream check disc assembly  6  each operate to prevent backflow. Any backflow liquid flowing upstream past the downstream check disc assembly  6  is diverted to a vent  7 , and prevented from flowing past the upstream check disc assembly  5 , which includes the threaded cap. A check plate  8 , which is an integral part of the threaded cap and a part of the check disc assembly  5 , is provided with a series of flow ports positioned around the periphery allows downstream water flow to and past the upstream check disc. 
         [0034]    In the normal, open operating condition the backflow preventer  1  exhibits substantial flow turbulence as a result of the configuration of the inlet cavity components that increase head loss and chatter at low flow conditions. The prior art check disc assemblies  5  and  6  are captured by fitting the inside diameter of the disc into the stem and holding flat by a plate/washer of equal diameter to the disc. The check discs are retained by means of swaging or riveting the hollow end of the stem and maintaining it tightly against a step in the stem. This assembly technique presents the possibility of stem wall cracks during assembly which can lead to a possible leak path past the check disc and failure of the check discs to hold static differential pressures. 
         [0035]    As described below, these deficiencies in the prior art have been corrected. More specific description of the elements of the prior art backflow preventer is set out below as part of the description and discussion of the novel features of the novel backflow preventer that is the subject of this application. 
       General Description of the Preferred Embodiment 
       [0036]    Referring now to  FIGS. 2-10 , a general description of the backflow preventer  10  and a detailed description of its components is provided, and proceeds in the flow direction from the inlet end to the outlet end. As shown generally in  FIGS. 2-5 , a threaded union nut  12  receives a tailpiece  14 , rubber washer  16 , and a convex strainer  20 , and secures these elements in a threaded cap  22 . An upstream check plate assembly  30  includes an annular check plate  32  that is provided with a series of flow ports  33  positioned around the flow axis of the check plate  32 . The check plate also includes a plurality of central flow ports  37 . 
         [0037]    The check plate  32  is mounted for axial movement on a check stem  34 , on which is positioned a check spring  36 . The check stem  34  moves axially between open and closed positions in a hub  39  formed concentrically in the check plate and supported by radially extending spokes. The check plate  32  supports a flexible diaphragm  38 , the outer periphery of which is captured between the check plate  32  and a diaphragm support ring  40  provided with a series of slotted recesses  44  around its inner peripheral surface. The check stem  36  is integrally formed on the end of an upstream check disc  42  that bears against the inner portion of the downstream side of the diaphragm  38 . The upstream check disc  42  is backed by a rubber check seat disc  41  that provides rigid support to the upstream check disc  42  and a seal to the diaphragm  38  around the diaphragm opening  43 . This is best shown in  FIGS. 2 and 9 . 
         [0038]    The check stem  34  extends through an axially-extending aperture  35  in the check plate  32 . The check spring  36  is compressed by flow pressure in the system against the upstream side of the upstream check disc  42  during normal operation, and allows water flow through the diaphragm opening  43  of the diaphragm  38 . The check plate assembly  30  is enclosed within a void defined by the cap  22  and a centrally-positioned valve housing  60 . The valve housing  60  includes an axially-extending housing wall  62 . A vent  64  communicates through a port  65  with the interior of the valve housing  60 . 
         [0039]    As shown in  FIGS. 2-5 and 10 , a downstream check plate assembly  80  is positioned on the downstream side of the backflow housing  60 , and includes a stem  82  integrally formed with a check disc  84 , with a spring  86  carried on the stem  82 . The check disc  84  is backed by a washer  88 . The downstream side of the valve housing  60  includes three wedge-shaped flow ports  90  defined by three spokes  92  that permits water flow downstream through the flow ports  90  and downstream out of the backflow preventer  10 . The spokes  92  support a concentric hub  94  in which is formed an aperture  66  in which the stem  82  of the check disc  84  is mounted for axial movement. 
         [0040]    Normal flow through the backflow preventer  10  compresses spring  86  as the check disc  84  is urged downstream and allows flow through the ports  90 . A tailpiece  98  is captured in a threaded union nut  100  which is threaded onto the downstream end of the housing  60 . A rubber washer  102  seals the union nut  100  against the downstream end of the housing  60 . 
       Upstream Check Plate Assembly 
       [0041]    The design and operation of the upstream check plate assembly  30  is explained in further detail by reference to  FIGS. 2-5  by first noting that the check disc  42  and the check disc stem  34  are integrally-formed, thereby avoiding the need to swage, rivet or weld the two elements together, as in the prior art. This avoids misalignment and the creation of a possible leak path when the wall of the stem  34  is not uniformly expanded or is otherwise compromised. The configuration and design of the flow ports  33  on the check plate  32  and the profile of the slotted recesses  44  of the diaphragm support ring  40  enable the diaphragm  38  to better withstand back-pressure and hydrostatic testing. The thickest part of the diaphragm  38  is exposed to the maximum pressure conditions, resulting in greater part longevity and reliability. Greater flow is allowed below the contact area of the seat disc  43  and the diaphragm  38 , thereby improving flow capacity and head loss reduction. 
         [0042]    The check disc  42  has a convex shape in the downstream direction. This convex shape provides greater strength and rigidity in the area of the stem  34 , and directs the flow around the check disc  42  in the downstream direction with less turbulence. 
         [0043]    In addition, the combined effect of the flow ports  33  positioned around the flow axis of the check plate  32  and the central flow ports  37  permit greater and more direct downstream flows in the upstream check plate assembly  30 . This is best shown by comparing the flow paths in the prior art backflow preventer  1  in  FIG. 2  with the improved backflow preventer  10  in  FIG. 5 . Note that the arrows indicating the flow path progress more directly and with less deflection through the check plate  32  and through the central opening in the diaphragm  38 . 
       Downstream Check Plate Assembly 
       [0044]    The design and operation of the downstream check plate assembly  80  is explained in further detail by reference to  FIGS. 2-5 and 10 . The downstream check disc  84  and the check disc stem  82  are integrally-formed, thereby avoiding the need to swage, rivet or weld the two elements together, as in the prior art. This avoids misalignment and the creation of a possible leak path when the wall of the stem  82  is not uniformly expanded or is otherwise compromised. The check disc  84  has a convex shape in the downstream direction. This convex shape provides greater strength and rigidity in the area of the stem  82 , and directs the flow around the check disc  84  in the downstream direction with less turbulence. 
         [0045]    In the event of backflow leakage past the check disc  84  as may be caused by several reasons, including debris caught between the check disc  84  and the housing  82 , the backflow is diverted to the vent  64 , as shown in  FIG. 4 . This diversion occurs when the backflow pressure forces the downstream-facing rib of the diaphragm  38  away from sealing engagement with the axially-extending housing wall  62 . Water passes between the diaphragm  38  and the housing wall  62  and drains out of the vent  64  to atmosphere. 
         [0046]    A backflow preventer according to the invention have been described with reference to specific embodiments and examples. Various details of the invention may be changed without departing from the scope of the invention. Furthermore, the foregoing description of the preferred embodiments of the invention and best mode for practicing the invention are provided for the purpose of illustration only and not for the purpose of limitation, the invention being defined by the claims.