Abstract:
A backflow preventor that generally includes a modular fluid arrangement having a modular strut, a one-piece modular cage, a relief valve fluidly connected to the modular cage, and at least one in-line check valve removably housed in the modular cage. In operation, when backflow occurs, pressure in a chamber of the relief valve increases to provide a passageway for fluid to flow out of the modular cage, through the relief valve, to the environment. When the backflow stops, the pressure in the chamber decreases and the passageway closes, moving the fluid through the interior of the modular cage.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of U.S. Provisional Application Ser. No. 60/646,079, filed Jan. 21, 2005. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a backflow preventor and, more particularly, to a modular fluid arrangement for a check valve to prevent backflow through the check valve.  
         [0004]     2. Description of Related Art  
         [0005]     Fluid valves generally include a main body having two ends. The main body also forms an internal flow cavity that fluidly connects the two ends and houses internal valves. In a typical installation, one end of the main body is connected to a fluid inlet pipe and the other end is connected to a fluid outlet pipe. Fluid flows from the fluid inlet pipe, through the internal flow cavity, is stopped, directed, or left unimpeded by the internal valves, and exits through the fluid outlet pipe. Such fluid valves can include backflow prevention valves, which ensure that fluid flow always flows in one direction. When, for various reasons, fluid does try to flow backward, the safest and most effective device for stopping the backflow is a “reduced pressure principle” backflow valve.  
         [0006]     Some fluid backflow valves have movable parts, such as two independently acting check valves positioned in the internal flow cavity formed by a main body and, as a failsafe, a differential pressure relief valve (RV) attached to a port of the main body. The RV acts as a failsafe because, in a backflow condition, even if the check valves fail, the RV will ensure that no downstream fluid is permitted to flow into an upstream fluid supply line by dumping potential backflow fluid to the atmosphere. Generally, most RV&#39;s are controlled internally by a pressure differential acting across a diaphragm. Typically, high pressure acting on one side (i.e., high side) of a diaphragm will force a rubber seal ring to abut against a “seat” edge, thus creating a water-tight seal. When the force due to pressure acting on an opposite side (i.e., low side) of the diaphragm acting in conjunction with a spring exceeds the high side force, the seal and seat edge will separate and open up a flow path for the fluid to escape. In essence, the diaphragm acts as a switch that opens and closes the flow path of the RV. Because the RV operation depends heavily on the diaphragm, which is typically made of an elastomeric material, a larger size diaphragm is generally used to provide for a stronger, more robust and positive RV operation. However, the advantages of a larger diaphragm have to be weighed against the disadvantages associated with a larger size diaphragm, often resulting in an overall bulkier valve design.  
         [0007]     The repair, inspection, or replacement of the fluid valves (i.e., check valves and RV) within the backflow prevention valve typically requires the flow of fluid to be shut off. An inlet shutoff valve, or some other member, as shown in U.S. Pat. Nos. 1,969,432; 3,245,257; 3,946,754; 4,327,760; 5,392,803; 5,511,574; and 5,732,744, is typically positioned adjacent one end of the main body and an outlet shutoff valve is positioned adjacent the other end of the main body. In turn, each shutoff valve is connected, respectively, to the fluid inlet pipe or the fluid outlet pipe. The shutoff valves are required for testing and service of the backflow prevention valve. Access to internal components of such fluid valves is typically accomplished through one or more access ports or openings. Under certain regulatory codes, the main body, which houses the fluid valves, cannot be completely removed from the fluid handling system during routine maintenance and inspection of the valves. In other instances when the main body is in a location that is not easily accessible to maintenance personnel, maintenance and inspection of such valves can become difficult.  
         [0008]     In some fluid handling installations, a bypass line is often used to maintain fluid flow through the system, while selected ones of the fluid valves of the system are either being repaired, inspected, or replaced. This bypass line adds additional costs and takes up extra space in the fluid handling installation. In some installations, a minor disruption in the fluid flow may not result in serious adverse consequences downline of the fluid handling installation and a bypass line is not required. Therefore, if the time of repair, replacement, or inspection of a fluid valve can be minimized, an additional bypass line may not be required.  
         [0009]     Therefore, it is an object of the present invention to overcome the above-mentioned deficiencies by providing a modular fluid arrangement for a check valve that provides for easy maintenance and replacement of check valves, with minimal disruption of the flow in a fluid handling installation. It is also desirable to provide a compact and space-efficient modular fluid arrangement, while providing a strong, robust, and positive RV operation.  
       SUMMARY OF THE INVENTION  
       [0010]     The present invention provides for a modular fluid arrangement for a check valve, e.g., a check valve assembly, that includes, among other things, a modular strut and a modular cage. The modular strut includes an inlet body and an outlet body and defines a modular cage receiving area therebetween. The modular cage having a first open end and a second open end and defining an interior cavity therebetween is adapted to be received by the modular cage receiving area of the modular strut. The interior cavity of the modular cage, which is adapted to be in fluid communication with the inlet body and the outlet body of the modular strut, is also adapted to receive at least one check valve. A differential pressure relief valve can be fluidly connected to the modular cage, wherein the pressure relief valve is adapted to be in fluid communication with the inlet body and the outlet body of the modular strut. The pressure relief valve has a biased seat, a rubber seal that remains stationary during operation, a diaphragm, a spring, and a piston that allows fluid to flow centrally out of the modular cage when pressure breaks the seal between the seat and the rubber seal. The fluid flows through the seat, diaphragm, spring, and piston.  
         [0011]     The present invention also provides for a check valve assembly that includes the modular fluid arrangement having the modular cage and the modular strut previously discussed, wherein the modular cage is removably secured to the modular strut. A plurality of check valves removably sealed within the interior cavity of the modular cage are in fluid communication with the inlet body and the outlet body of the modular strut.  
         [0012]     The modular fluid arrangement of the invention compensates for the expansion and contraction of the assembly under the effects of thermal expansion and contraction, water hammer, pressure fluctuations, and part length fluctuations for the protection of the valve components and for the preservation of gasket integrity.  
         [0013]     The present invention also provides for a method of installing check valves in line with respect to a fluid conduit using a modular fluid arrangement as previously discussed. The method includes, among other things, inserting at least one check valve into the interior cavity of the modular cage; inserting the modular cage into the modular cage receiving area; removably securing the modular cage to the modular strut; and installing the modular fluid arrangement in line with respect to a fluid conduit.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a top, side orthogonal view of a check valve assembly incorporating features of, and made in accordance with, the present invention;  
         [0015]      FIG. 2  is an exploded top, side orthogonal view of the check valve assembly shown in  FIG. 1 ;  
         [0016]      FIG. 3  is a top elevational view of the modular strut shown in  2 ;  
         [0017]      FIG. 4  is a side elevational view of the modular strut shown in  FIG. 3 ;  
         [0018]      FIG. 5  is a view taken along lines V-V of  FIG. 3 ;  
         [0019]      FIG. 6  is a top, side orthogonal view, partially in section, of the modular fluid arrangement of the check valve assembly shown in  FIG. 2 ;  
         [0020]      FIG. 7  is a bottom, side orthogonal view of the modular cage of the modular fluid arrangement shown in  FIG. 6 ;  
         [0021]      FIG. 8  is a view taken along lines VIII-VIII of  FIG. 1 ;  
         [0022]      FIG. 9  is an exploded view of the modular fluid arrangement of the check valve assembly shown in  FIG. 2  showing two check valves removably attached to each other;  
         [0023]      FIG. 10  is a view similar to the view of  FIG. 9  showing the check valves detached from each another;  
         [0024]      FIG. 11  is a view similar to the view of  FIG. 9  showing fasteners removed from the modular fluid arrangement;  
         [0025]      FIG. 12  is a view similar to the view of  FIG. 9  showing a pressure relief valve detached from the modular fluid arrangement;  
         [0026]      FIG. 13  is a sectional, elevated side view of the pressure relief valve of the check valve assembly shown in  FIG. 8 ;  
         [0027]      FIG. 14  is an exploded view of the pressure relief valve shown in  FIG. 13 ;  
         [0028]      FIG. 15  is an exploded view of a relief valve cartridge of the pressure relief valve shown in  FIG. 14 ;  
         [0029]      FIG. 16  is a view similar to the view of  FIG. 8  showing another non-limiting embodiment of a pressure relief valve of the check valve assembly shown in  FIG. 1 ; and  
         [0030]      FIG. 17  is an exploded view of the pressure relief valve shown in  FIG. 16 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0031]     As used herein, spatial or directional terms, such as “inner”, “outer”, “left”, “right”, “up”, “down”, “horizontal”, “vertical”, and the like, relate to the invention as it is shown in the drawing figures. However, it is to be understood that the invention can assume various alternative orientations and, accordingly, such terms are not to be considered as limiting. Further, all numbers expressing dimensions, physical characteristics, and so forth, used in the specification and claims are to be understood as being modified in all instances by the term “about”. Accordingly, unless indicated to the contrary, the numerical values set forth in the specification and claims can vary depending upon the desired properties sought to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Moreover, all ranges disclosed herein are to be understood to encompass any and all subranges subsumed therein. For example, a stated range of “1 to 10” should be considered to include any and all subranges between (and inclusive of) the minimum value of 1 and the maximum value of 10; that is, all subranges beginning with a minimum value of 1 or more and ending with a maximum value of 10 or less, e.g., 1 to 6.7, or 3.2 to 8.1, or 5.5 to 10.  
         [0032]     Before discussing non-limiting embodiments of the invention, it is understood that the invention is not limited in its application to the details of the particular non-limiting embodiments shown and discussed herein since the invention is capable of other embodiments. Further, the terminology used herein to discuss the invention is for the purpose of description and is not of limitation. Still further, unless indicated otherwise in the following discussion, like numbers refer to like elements.  
         [0033]      FIG. 1  shows a check valve assembly  10  made in accordance with the present invention. The assembly  10  includes a modular fluid arrangement  12  having one or more in-line check valves (and, preferably, two check valves  14  and  14 ′ having outer surfaces  15  as shown in  FIGS. 8-12 ) received within the modular fluid arrangement  12 . Referring to  FIGS. 1 and 2 , the modular fluid arrangement  12  includes a modular strut  16  having an inlet body  18  and an outlet body  20  and defining a modular cage receiving area  22  therebetween, and a one-piece modular cage  50  removably secured to the modular strut  16  and received by the modular cage receiving area  22 . The modular strut  16  includes a pair of spacers  24  (shown in  FIG. 2 ) separating the inlet body  18  from the outlet body  20 .  
         [0034]     Referring to  FIGS. 2-5 , the inlet body  18  of the modular strut  16  forms an inlet receiving surface  26 , a fluid inlet channel  28 , and a first connector  30 , and the outlet body  20  forms an outlet receiving surface  34 , a fluid outlet channel  36 , and a second connector  38 . The first connector  30  and second connector  38  are adapted to connect to a fluid conduit (not shown). The fluid inlet channel  28  extends from the inlet receiving surface  26  to the first connector  30  of the inlet body  18 , and the fluid outlet channel  36  extends from the outlet receiving surface  34  to the second connector  38  of the outlet body  20  of the modular strut  16 .  
         [0035]     Referring to  FIGS. 1-5 , the pair of spacers  24  are each removably connected to the inlet body  18  and the outlet body  20  by fasteners  25 , such as bolts. The spacers  24 , which can vary in length depending on the length of the modular cage  50 , can be sized to reduce the movement of the inlet body  18  and the outlet body  20  with respect to one another, e.g., toward one another. A first shutoff valve  42  having a first handle  44  is positioned between the first connector  30  and the inlet receiving surface  26  and is integrally formed with the inlet body  18  of the modular strut  16 . A second shutoff valve  46  having a second handle  48  is positioned between the second connector  38  and the outlet receiving surface  34  and is integrally formed with the outlet body  20  of the modular strut  16 . The modular strut  16  can be made of metal or a rigid polymeric material, such as, but not limited to plastic and/or glass and/or steel fiber-reinforced plastic.  
         [0036]     Referring to  FIGS. 2 and 6 - 12 , and in particular to  FIG. 6 , the modular cage  50  includes a body  52  having a first open end  54 , a second open end  56 , an interior surface  58 , and an exterior surface  60 , wherein the interior surface  58  defines an interior cavity  62  between the first open end  54  and the second open end  56  of the body  52  of the modular cage  50 . Referring to  FIG. 8 , the interior cavity  62  of the body  52  of the modular cage  50  is adapted to be in fluid communication with the fluid inlet channel  28  of the inlet body  18  and the fluid outlet channel  36  of the outlet body  20  of the modular strut  16 . Referring to  FIGS. 9-12 , the interior cavity  62  of the body  52  of the modular cage  50  is also adapted to receive the in-line check valves  14 ,  14 ′. The in-line check valves  14 ,  14 ′ are similar to those shown and described in U.S. Pat. No. 6,513,543 to Noll et al., which is herein incorporated by reference. The modular cage  50  can be geometric shaped, such as tubular shaped, rectangular shaped, hexagonal shaped, or other polygonal shape, and can be made of metal or a polymeric material, such as, but not limited to plastic and/or glass and/or steel fiber-reinforced plastic.  
         [0037]     Referring back to  FIG. 1 , the modular cage  50  is removably secured within the modular cage receiving area  22  of the modular strut  16 . As shown in  FIGS. 2 and 3 , a plurality of receiving slots  21  are defined in the inlet body  18  and the outlet body  20 , wherein the receiving slots  21  are adapted to receive fasteners for securing the modular cage  50  to the modular strut  16  in a manner discussed below. Referring to  FIGS. 2 and 6 - 8 , at least one tap  64  (and, preferably, a plurality of taps  64 ) extends from the exterior surface  60  of the body  52 , wherein the taps  64  are in fluid communication with the interior cavity  62  of the body  52  of the modular cage  50 . The taps  64  can be internally threaded for attaching additional components, such as pressure gauges and flow gauges, to the check valve assembly  10 .  
         [0038]     Referring to  FIGS. 6 and 7 , a valve tap  66  having at least one opening  67  (preferably two openings  67 ,  67 ), which can be positioned on the body  52  of the modular cage  50  opposite the tap(s)  64 , extends from the exterior surface  60  of the body  52 , wherein the openings  67 ,  67 ′ are in fluid communication with the interior cavity  62  of the body  52  of the modular cage  50 . The modular cage  50  also defines a first protrusion  70  and a second protrusion  71  opposed from each other and extending from the body  52  adjacent the valve tap  66 , wherein the protrusions  70 ,  71  each define at least one slot  72  (preferably two slots  72  in the first protrusion  70  and one slot in the second protrusion  71 ) for receiving fasteners for attachment of a pressure relief valve  68  to the valve tap  66 . The slots  72  can be internally threaded to receive threaded fasteners, such as bolts  69  (see  FIGS. 9-11 ). Alternatively, the protrusions  70 ,  71  can have threaded inserts molded into the slots  72  of the body  52  of the modular cage  50 .  
         [0039]     Referring to  FIGS. 6-8 , and in particular to  FIG. 8 , an upstream pressure port  73  is provided in the first protrusion  70  and is in fluid communication with the interior cavity  62  of the body  52  of the modular cage  50 . The differential pressure relief valve  68  can be removably attached to the valve tap  66 , wherein the pressure relief valve  68  is in fluid communication with the interior cavity  62  of the body  52  of the modular cage  50  via the openings  67 ,  67 ′ and the pressure port  73 . The relief valve  68 , which can be hydraulically operated, protects against fluid flow toward the fluid inlet channel  28 , e.g., in direction F 2  (shown in  FIG. 1 ), by discharging fluid from the interior of the modular cage  50  through the relief valve  68  along flow path F 1  to the outside atmosphere or environment as shown in  FIG. 8 . A detailed description of the pressure relief valve  68  is discussed later.  
         [0040]     Referring to  FIGS. 2 and 8 - 12 , the modular cage  50  further includes a removable end piece  74  having a first side  76  and a second side  78  and defining a central opening  80 , wherein the end piece  74  is adapted to engage the first open end  54  of the body  52  of the modular cage  50 . An annular member  82  surrounding the central opening  80  and extending away from the second side  78  of the end piece  74  is adapted to be received within the interior cavity  62  of the body  52  of the modular cage  50 . A first bracket  84  is attached to the periphery of the end piece  74  and extends away from the first side  76 , wherein the first bracket  84  defines a plurality of slots  85  adapted to receive end piece fasteners  88  (see  FIG. 2 ) for securing the modular cage  50  to the modular strut  16 . A second bracket  86 , which is similar to first bracket  84 , is attached to the exterior surface  60  at the second open end  56  of the body  52  of the modular cage  50  and extends away from the second open end  56 , wherein the second bracket  86  defines a plurality of slots  87  adapted to receive end piece fasteners  88 ′ for securing the modular cage  50  to the modular strut  16 . The end piece fasteners  88 ,  88 ′ can be threaded fasteners, such as bolts, to capture the ends of the fasteners in the slots  21  of the modular strut  16 .  
         [0041]     Referring to  FIGS. 2 and 8 , an annular groove  90  defined on the first side  76  of the end piece  74  is adapted to receive a first sealing gasket  92  (shown in  FIG. 8 ). The first sealing gasket  92  is adapted to provide a seal between the inlet receiving surface  26  of the inlet body  18  of the modular strut  16  and the first side  76  of the end piece  74 . A second sealing gasket  94  may be positioned on the annular member  82  (shown in  FIG. 8 ), wherein the second sealing gasket  94  is adapted to provide a seal between interior surface  58  of the interior cavity  62  of the body  52  of the modular cage  50  and the annular member  82  of the end piece  74 . A second annular groove  90 ′ defined on the exterior surface  60  of the second open end  56  of the body  52  of the modular cage  50  is adapted to receive a third sealing gasket  96  as shown in  FIG. 8 . The third sealing gasket  96  is adapted to provide a seal between the interior cavity  62  of the body  52  of the modular cage  50  and the outlet receiving surface  34  of the outlet body  20  of the modular strut  16 . The gaskets  92 ,  94 , and  96 , which can be made of an elastomeric material, such as rubber, can be annular shaped, such as O-rings as shown for the sealing gasket  92  (shown in  FIG. 8 ), or flat gaskets (not shown). Alternatively, any type of sealing arrangement can be used, such as an arrangement having one fluid seal or a plurality of fluid seals.  
         [0042]     Referring to  FIGS. 8-12 , the plurality of check valves  14 ,  14 ′ can be removably seated within the interior cavity  62  of the body  52  of the modular cage  50 , wherein a valve gasket  98  can be positioned on the outer surfaces  15  of each check valve  14 ,  14 ′. When the check valves  14 ,  14 ′ are received within the interior cavity  62  of the body  52  of the modular cage  50 , the gasket  98  is compressed against the interior surface  58  of the interior cavity  62  and the outer surfaces  15  of the check valves  14 ,  14 ′, thus sealing the check valves  14 ,  14 ′ within the interior cavity  62  of the body  52  of the modular cage  50  (shown in  FIG. 8 ). When the end piece  74  is placed adjacent the first open end  54  of the body  52  of the modular cage  50 , the modular cage  50  can be received within the modular cage receiving area  22  of the modular strut  16 . Referring to  FIGS. 2 and 8 , a wedge surface or angled surface  100  defining a central opening and defining the second open end  56  of the body  52  of the modular cage  50  abuts against the outlet receiving surface  34  of the outlet body  20  of the modular strut  16 . The wedge surface  100  enables the modular cage  50  and the end piece  74  to be held in place by a tight fit between the first side  76  of the end piece  74  and the inlet receiving surface  26  and the outlet receiving surface  34  of the modular strut  16 . As discussed and not limiting to the invention, the modular cage  50  can be secured to the modular strut  16  via fasteners  88 ,  88 ′ passing through slots  85 ,  87  of brackets  84 ,  86 , respectively, and receiving slots  21  of the inlet body  18  and the outlet body  20  of the modular strut  16 . Although the check valves  14 ,  14 ′ are sealed within the modular cage  50 , the modular cage  50  can move or float a distance X (see  FIG. 8 ) between the second side  78  of the end piece  74  and the first open end  54  of the body  52  of the modular cage  50 . The modular cage  50  and the modular strut  16  are free to expand and contract in a telescoping action relative to one another in a longitudinal direction represented by arrow X 1  (shown in  FIG. 8 ), with a resultant increase or decrease of the distance X, thereby allowing for protection of the modular cage  50  from damage resulting from water hammer, and preservation of the integrity of the gaskets  92 ,  96  under the effects of water hammer, thermal expansion and contraction, pressure fluctuations, and part length variations.  
         [0043]     Referring to  FIGS. 8 and 13 - 15  as needed, the pressure relief valve  68  includes a rubber seal  102 , a seal retainer  104 , a fastener  103 , such as a screw, a relief valve cartridge  105  defining a central passageway P, a main seal  106 , and a port seal  108 . The seal retainer  104  secures the rubber seal  102  to the valve tap  66  of the body  52  of the modular cage  50  via the screw  103  as shown in  FIG. 13 . The rubber seal  102  remains stationary during operation of the relief valve  68 . Referring to  FIGS. 13-15 , and particularly to  FIG. 15 , the cartridge  105  includes a valve seat  110 , a spring guide  112 , a spring  114 , a diaphragm  116 , a valve piston  118 , and a piston seal  120 . The spring  114 , spring guide  112 , and diaphragm  116  are positioned between the piston  118  and the valve seat  110 , wherein the spring  114  and spring guide  112  are defined within the passageway P, and the piston seal  120  is positioned around the piston  118  (see  FIG. 13 ). The piston  118  and spring guide  112  are biased by spring  114 , wherein the spring guide  112  abuts against the seal retainer  104 . The cartridge  105  is held together by threads  119  on an underside of the valve seat  110 , which co-acts with corresponding threads  121  in the piston  118  (clearly shown in  FIG. 13 ). Alternatively, the cartridge  105  can be held together by a plurality of fasteners or by some other means of permanent adhesion of the valve seat  110  to the piston  118 . The spring guide  112  serves the purpose of trapping the spring  114  inside of the cartridge  105 , as well as providing a stanchion for transmitting the spring force between the piston  118  and the seal retainer  104  to bias the valve seat  110  away from the valve tap  66  into an open position. Also, the spring guide  112  provides for a fluid flow path F (shown in  FIGS. 8 and 13 ) that does not cross the spring  114 . Alternatively, the spring guide  112  can be eliminated and the spring  114  can press directly on the seal retainer  104 . In this case, the flow path F would cross over the spring  114  as shown in  FIG. 16 .  
         [0044]     Referring to  FIGS. 8-13 , the relief valve  68  also includes a first valve body  122  and a second valve body  124  defining an outlet  125 , wherein each body  122 ,  124  defines an interior cavity  126 ,  126 ′ and a pressure port  128 ,  128 ′, respectively, partitioned by the diaphragm  116  and containing the relief valve cartridge  105 . Alternatively, the rubber seal  102  (see  FIG. 13 ) can also be secured within the interior cavity  126  of the first valve body  122 , apart from the body  52  of the modular cage  50 . The first valve body  122  is attached to the second valve body  124 , wherein the main seal  106  and the port seal  108  (see  FIG. 13 ) are positioned therebetween. The attachment of the first valve body  122  to the second valve body  124  can be done by a mechanical arrangement, such as with the use of a nut and bolt arrangement. The relief valve  68  can be attached to the valve tap  66  by a plurality of fasteners, such as bolts  69 , passing though holes  123  (shown in  FIGS. 12 and 14 ) defined in the valve bodies  122 ,  124  and received with the slots  72  defined in the protrusions  70 ,  71  of the body  52  of the modular cage  50  (see  FIGS. 7 and 13 ).  
         [0045]     When the relief valve  68  is in a normally closed position, the valve seat  110  abuts against the rubber seal  102  (partially shown in phantom in  FIG. 8  and designated by P), thus closing off the flow path F. In the closed position, the interior cavity  126 ′ of the second valve body  124  below the diaphragm  116  is filled with fluid via the pressure ports  73 ,  128  and  128 ′, whereby the pressure in the interior cavity  126 ′ (i.e., high side), e.g., the fluid pressure, is greater than the pressure in the interior cavity  126  (i.e., low side). This causes the diaphragm  116  to flex in the direction of arrow A 1  (see  FIGS. 8 and 13 ), which raises the valve seat  110  and piston  118 , thus compressing the spring  114 , thereby sealing the valve seat  110  against the rubber seal  102 .  
         [0046]     When the relief valve  68  is in an open position (shown in  FIGS. 8 and 13 ), the valve seat  110  is spaced from the rubber seal  102 , thereby allowing fluid to flow through the flow path F defined by the valve seat  110 , diaphragm  116 , spring  114 , piston  118 , and outlet  125  of the second valve body  124 . This open position occurs when the force on the low side of interior cavity  126 , due to pressure acting in conjunction with the spring, is greater than the force on the high side of interior cavity  126 ′. This causes the diaphragm  116  to flex in the direction of arrow A 2 , which lowers the valve seat  110  and piston  118 , thus expanding the spring  114 , thereby breaking the seal between the valve seat  110  and the rubber seal  102 .  
         [0047]     The relief valve  68  provides for a strong/positive relief valve operation while maintaining relatively compact overall dimensions. The design of relief valve  68  also provides for easy inspection, repair, and replacement of the rubber seal  102  and for easy inspection and replacement of the relief valve cartridge  105  by removing the cartridge  105  from the valve bodies  122 ,  124 .  
         [0048]      FIGS. 16 and 17  show another non-limiting embodiment of a relief valve of the invention, designated by the number  130 , that is similar to relief valve  68  with differences noted below. Like reference numerals will be used for like parts. Relief valve  130  does not include a spring guide  112 , as in relief valve  68 . The spring  114  in relief valve  130  abuts directly against the seal retainer  104 . The seal retainer  104 , which secures the rubber seal  102  to the body  52  of the modular cage  50 , includes four prongs  132  (only two are shown in  FIG. 16 ) extending from a surface of the seal retainer  104 . The prongs  132  function as a guide for the valve seat  110 . Relief valve  130  also operates similar to relief valve  68 , except that the flow path F of the relief valve  130  crosses over the spring  114  when in an open position.  
         [0049]     The present invention also provides for a method of installing check valves  14 ,  14 ′ in line with respect to a fluid conduit using the modular fluid arrangement  12  of the present invention. Referring to  FIGS. 9-11 , check valves  14 ,  14 ′ having valve gasket  98  positioned on the outer surfaces  15  of each check valve  14 ,  14 ′ are inserted into the interior cavity  62  of the body  52  of the modular cage  50  via the first open end  54 . A second gasket  94  is placed on annular member  82  of end piece  74 , and the end piece  74  is inserted through the first open end  54  of the interior cavity  62  of the body  52  of the modular cage  50 . Gaskets  92  and  96  are placed adjacent the first side  76  of the end piece  74  and the second open end  56  of the modular cage  50 , respectively. Next, the modular cage  50  is inserted into the modular cage receiving area  22  of the modular strut  16 , wherein the wedge surface  100  of the body  52  is positioned adjacent the outlet receiving surface  34  of the outlet body  20  of the modular strut  16 . The modular cage  50  and the modular strut  16  are secured to each other via the fasteners  88 ,  88 ′ passing through slots  85 ,  87  of brackets  84 ,  86 , respectively, and receiving slots  21  in the inlet body  18  and the outlet body  20  of the modular strut  16 . Finally, the modular fluid arrangement  12  is installed in line with respect to a fluid conduit (not shown) at the inlet body  18  and the outlet body  20  of the modular strut  16 . The fluid conduit, such as a pipe, can be threaded, welded, flanged, or bolted onto the first connector  30  of the inlet body  18  and the second connector  38  of the outlet body  20  of the modular strut  16 .  
         [0050]     In operation, the check valves  14 ,  14 ′ in the modular fluid arrangement  12  open when fluid flows from the inlet body  18  of the modular strut  16  through check valves  14 ,  14 ′ in the interior cavity  62  of the modular cage  50 , exiting through the outlet body  20  of the modular strut  16  as indicated by arrow F 1  shown in  FIG. 1 . Should fluid flow in an opposite direction as indicated by arrow F 2 , the check valves  14 ,  14 ′ close, thereby preventing the flow of fluid through the modular fluid arrangement  12 . Should the fluid pressure in the interior cavity  62  of the body  52  of the modular cage  50  become greater than the upstream pressure at pressure port  73 , the relief valve  68  opens as discussed above to open up a flow path F for fluid to escape into the atmosphere or the environment.  
         [0051]     Periodically, the check valves  14 ,  14 ′ of the check valve assembly  10  must be inspected. This can be done by shutting down the fluid flow using shutoff valves  42  and  46  and loosening the fasteners  88 ,  88 ′, thereby removing the modular cage  50  from the modular cage receiving area  22  of the modular strut  16 . Each of the check valves  14 ,  14 ′ can be removed from the interior cavity  62  of the modular cage  50  and inspected, repaired, and/or replaced, while the modular strut  16  remains in line with respect to the fluid handling installation. The check valve assembly  10  provides for easy accessibility for repair, inspection, or replacement of check valves  14 ,  14 ′, thus minimizing downtime in a fluid handling installation.  
         [0052]     While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. The presently preferred embodiments described herein are meant to be illustrative only and not limiting as to the scope of the invention, which is to be given the full breadth of the appended claims and any and all equivalents thereof.