Abstract:
A gas flow control valve configured to facilitate back-to-back mounting with a second, similarly constructed valve. The gas valve includes a valve body defining an inlet port and an outlet port, the inlet and outlet ports being surrounded by seal forming O-rings of different diameters. Flanges surrounding the inlet and outlet ports are configured with distinct attachment features for accommodating bolts for securing one valve in series with another or with a pipe flange or other auxiliary device, the inlet flange having either a slot dimensioned to hold and prevent rotation of a bolt head or nut, or a clearance slot permitting use of a wrench, and the outlet flange having the other slot configuration.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a gas valve. More particularly, it relates to a gas valve configured for back-to-back mounting with a second, similarly designed valve. 
     A variety of different gas-based heating equipment are available for use with various commercial/industrial applications. These appliances generally employ one or more gas burners, each supplied with liquefied petroleum (LP), natural or manufactured gas. Additionally, commercial/industrial gas heating equipment installations include one or more valves for controlling the flow of gas to the burner. In this regard, a number of different gas valve types exist, each having certain performance features and corresponding costs. For example, valves typically used in gas flow applications include diaphragm valves, solenoid valves, vent valves, shut-off valves, metering valves, butterfly valves, and fluid power valves, to name but a few. 
     While all of the above-identified valves are available for controlling gas flow, in many instances, a specific valve combination, or valve train, is required. As a point of reference, with most large scale commercial/industrial gas burning applications, the gas flow rate and consumption volume is very high. In light of the potential hazards associated with these applications, the Underwriters Laboratories Inc. (UL) has established valve train safety standards for commercial/industrial gas heating equipment. In particular, UL 795 sets forth the following valve requirements for mechanical-draft or atmospheric gas burners. For an installation having a gas burner input of 400,000 to 2,500,000 Btu/H (British thermal unit per hour), one valve rated for safety shut-off service (SSOV) is required. For installations having a gas burner input in the range of 2,500,000 to 5,000,000 Btu/H, two SSOV&#39;s in series, or one SSOV of the type incorporating a valve seal overtravel interlock, is required. For installations utilizing a gas burner input in the range of 5,000,000 to 12,500,500 Btu/H, two SSOV&#39;s in series, one of which incorporates a valve seal overtravel interlock, is required. Finally, for gas burner inputs in excess of 12,500,000 Btu/H, two SSOV&#39;s in series, one of which incorporates a valve seal overtravel interlock, is required. Further, for installations having burner inputs of 12,500,00 Btu/H or more, if the fuel gas has a specific gravity of less than 1.0, a normally open vent valve must be incorporated in line between the two SSOV&#39;s. 
     The above-provided UL code essentially dictates the required valve train configuration for most commercial/industrial gas burner applications. Pursuant to the UL code, then, many gas burner supply lines must include two safety shut-off valves mounted in series. Further, certain other applications require an additional vent valve disposed between the two safety shut-off valves. It should be noted that customers and/or installers may prefer to use two or more valves mounted in series for reasons other than UL code compliance. Currently, installation of two valves in series is relatively burdensome. Regardless of the exact valve type, virtually every gas valve includes a valve body defining an inlet port and an outlet port. Each of the inlet port and outlet port are internally threaded. Thus, in order to assemble two gas valves in series, a short length of appropriately sized pipe (or a “pipe nipple”) must be formed and threaded. The pipe nipple is then threaded into the outlet port of the first valve and the inlet port of the second valve. Obviously, this labor intensive procedure is time consuming, and increases the overall length of the valve train. The mounting procedure is further complicated where a third valve, such as a vent valve, is necessary. An additional concern arises when one of the valves malfunctions. Replacement of the defective valve is cumbersome and therefore time-consuming. In short, current gas valve designs do not allow for a direct mounting of two gas valves back-to-back; instead, a pipe nipple must be used. 
     Recently, in response to the frequent installation requirement of two valves mounted in series and the associated difficulties of assembly, a singularly cast, two valve body design has been made available. The integrally casted, dual valve device does simplify the gas line assembly procedure in that it is no longer necessary to create and install a pipe nipple between the two valves. Unfortunately, however, certain other problems may arise. For example, the user is limited to the type of valve(s) formed in the single casted device. In other words, where the integrally casted, dual valve device incorporates two fluid power valves, the user is not able to replace one of the valves with a less expensive diaphragm valve. Additionally, if one of the continuous casting valves malfunctions, the entire assembly must be replaced even though the second valve may still operate properly. 
     Code requirements for industrial gas burning equipment require the use of two or more series mounted valves for many applications. The widely accepted practice of connecting the valves with pipe nipples is time-consuming and, therefore, expensive. Thus, a need exists for a gas valve configured to be readily mounted to a second valve in a back-to-back fashion. 
     SUMMARY OF THE INVENTION 
     One preferred embodiment of the present invention provides a gas flow control valve comprising a valve body, an inlet O-ring and an outlet O-ring. The valve body includes an inlet portion and an outlet portion. The inlet portion defines an outlet port, whereas the outlet portion defines an outlet port. The inlet O-ring surrounds the inlet port for forming a seal between the inlet portion and an auxiliary device. Similarly, the outlet O-ring surrounds the outlet port for forming a seal between the outlet portion and another auxiliary device. While the inlet port and the outlet port preferably have the same diameter, the inlet O-ring has a diameter different from a diameter of the outlet O-ring. 
     The above-described gas valve may have a variety of internal control configurations, such as, for example, fluid power, diaphragm or solenoid arrangements. To this end, the gas valve functions in accordance with the internal elements. However, regardless of the internal control configuration, assembly of the gas valve as part of a valve train is simplified. For example, the auxiliary device may be a pipe adapter secured to the inlet portion or the outlet portion. The pipe adapter is sealed to the respective inlet portion or outlet portion via the inlet O-ring or outlet O-ring, respectively. Additionally, the gas valve of the present invention can be rapidly mounted to a similarly configured valve in a back-to-back fashion. For example, the outlet portion of the gas valve may be mounted to an inlet of the second valve. Once again, the outlet O-ring will form a seal between the two devices. Where the second valve is a gas valve in accordance with the present invention and therefore includes an inlet O-ring having a diameter different than a diameter of the outlet O-ring, a dual seal is achieved between the two valves, with each O-ring directly contacting the respective valve surfaces. 
     Another aspect of the present invention relates to a back-to-back valve train including a first valve and a second valve. The first valve comprises a valve body and an outlet O-ring. The valve body includes inlet portion defining an inlet port and outlet portion defining an outlet port. The outlet O-ring surrounds the outlet port. Similarly, the second valve comprises a valve body and an inlet O-ring. The second valve body includes an inlet portion defining an inlet port and an outlet portion defining an outlet port. The inlet O-ring surrounds the second valve inlet port. The outlet O-ring associated with the first valve has a diameter different from a diameter of the inlet O-ring associated with the second valve. With the above construction in mind, the first valve outlet portion is configured to abut the second valve inlet portion such that the first and second valves are mounted back-to-back. Further, the first valve outlet O-ring has a diameter different than a diameter of the second valve inlet O-ring such that each of the first valve outlet O-ring and the second valve inlet O-ring form a seal between the first valve outlet portion and the second valve inlet portion. In one preferred embodiment, the first valve further includes an outlet coupling means and the second valve includes an inlet coupling means. The outlet coupling means and the inlet coupling means are configured to rapidly couple the first valve outlet portion directly to the second valve inlet portion via a fastening device, such as a bolt and nut. Preferably, one of the outlet coupling means or inlet coupling means is configured to capture a portion of the fastening device. 
     Yet another aspect of the present invention relates to a method of mounting a first gas flow control valve and a second gas flow control valve back-to-back. The first gas flow control valve includes an outlet portion defining an outlet port. The second gas flow control valve includes an inlet portion defining an inlet port. The method includes securing a first O-ring to the outlet portion such that the first O-ring encircles the outlet port. A second O-ring is secured to the inlet portion such that the second O-ring encircles the inlet port. The second O-ring has a diameter different from a diameter of the first O-ring. The outlet portion is then directly coupled to the inlet portion whereby the first O-ring and the second O-ring each form a seal between the outlet portion and the inlet portion. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 is a perspective view of a fluid flow control valve in accordance with the present invention; 
     FIG. 2 is a perspective, exploded view of a valve train including two valves in accordance with the present invention; 
     FIG. 3 is an enlarged, side view of a portion of the assembled valve train of FIG. 2; 
     FIG. 4 is an enlarged, cross-sectional view of a portion of the assembled valve train of FIG. 2; and 
     FIG. 5 is a perspective, exploded view of an alternative embodiment valve train in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     One preferred embodiment of a gas flow control valve  10  is shown in FIG.  1 . Valve  10  includes a valve body  12 , an inlet O-ring  14  and an outlet O-ring  16 . Valve body  12  includes an inlet portion  18  and an outlet portion  20  (shown partially in FIG.  1 ). Inlet portion  18  defines an inlet port  22 ; whereas outlet portion  20  defines an outlet port (not shown). Upon final assembly, inlet O-ring  14  surrounds inlet port  22 . Similarly, outlet O-ring  16  surrounds the outlet port. 
     Relevant features of valve  10  are described in greater detail below. In general terms, however, valve  10  depicted in FIG. 1 conforms generally with a known fluid power, actuator controlled, gas valve. Thus, valve  10  is shown as including a bonnet  24  configured to receive a valve actuator (not shown) for controlling operation of internal valve components (not shown). It should be understood, however, that a valve in accordance with the present invention is in no way limited to a fluid power valve. Instead, valve  10  may be a diaphragm valve, a solenoid valve, a vent valve, a shut-off valve, a metering valve, a butterfly valve, etc. In short, the internal configuration and operation of valve  10  may correspond with any currently available or newly created gas flow control valve. 
     Valve body  12  preferably includes inlet portion  18 , outlet portion  20 , inlet coupling means  26 , an inlet mounting tab  28 , outlet coupling means  30 , an outlet mounting tab (not shown) and a component side  32 . Valve body  12  is preferably die casted from a rigid material, such as aluminum, so that the various components are integrally formed. 
     Inlet portion  18  defines inlet port  22 , and includes an exterior face  34  forming an annular groove  36 . In this regard, exterior face  32  is substantially flat both inside and outside of annular groove  36 . Annular groove  36  encircles inlet port  22  and is sized to receive inlet O-ring  14 . Thus, a diameter of annular groove  36  corresponds with a diameter of inlet port  22  such that annular groove  36  has a diameter slightly greater than that of inlet port  22 . Notably, inlet port  22  preferably is not interiorly threaded. 
     Outlet portion  20  (shown partially in FIG. 1) is highly similar to inlet portion  18  in that it defines outlet port (not shown) and includes an exterior face (not shown) forming an annular groove (not shown). The annular groove associated with outlet portion  20  encircles the outlet port and is sized to receive outlet O-ring  16 . As described in greater detail below, a diameter of the annular groove associated with outlet portion  20  is of a different size, preferably smaller, than a diameter of annular groove  34  of inlet portion  18 . 
     FIG. 1 depicts two inlet coupling means  26  located on opposite sides of inlet port  22 . For ease of illustration, only one of inlet coupling means  26  is described in detail, it being understood that each of inlet coupling means  26  are preferably identical. Inlet coupling means  26  is preferably integral with inlet portion  18  and includes an abutment surface  40  and a bearing surface  42  (shown partially in FIG.  1 ). Inlet coupling means  26  further forms a slot  44  extending from abutment surface  40  to bearing surface  42 , preferably in a direction parallel with an axis of inlet port  22 . Finally, bearing surface  42  is spaced from component side  32  by a gap  46 . As described in greater detail below, slot  44  is preferably sized to receive a portion of a fastening device, such as a bolt (not shown). To this end, slot  44  is longitudinally accessible through a lower opening  48 . Gap  46  is likewise open, and therefore accessible, both below and from a side of valve body  12 . 
     Inlet mounting tab  28  is preferably integrally formed with inlet portion  18 , extending downwardly (relative to the orientation of FIG. 1) therefrom. Inlet mounting tab  28  is flush with exterior face  34  of inlet portion  18  and includes a bore  50 . Bore  50  is preferably sized to axially receive a portion of a fastening device, such as a bolt (not shown). 
     Outlet coupling means  30  is preferably integrally formed with outlet portion  20  and includes a slot  60  extending between an exterior surface  62  and a base  64 . Slot  60  is defined by a first section  66  and a second section  68 . First section  66  is open at exterior surface  62  and is sized to allow for passage of a portion of fastening device, such as a bolt (not shown). Second section  68  is open at first section  66  and has a height greater than that of first section  66 . In particular, second section  68  is sized to capture an enlarged portion of a fastening device, as described in greater detail below. As shown in FIG. 1, a bearing surface  70  is generated at a transition from first section  66  to second section  68 . Finally, slot  60  is open, or accessible from, a side of valve body  12 . Notably, while FIG. 1 depicts one outlet coupling means  30 , it should be understood that a second outlet coupling means (not shown) is preferably formed at an opposite side of outlet port (not shown). 
     The outlet mounting tab (not shown) is preferably integrally formed with outlet portion  20 , extending downwardly (relative to the orientation of FIG. 1) therefrom. The outlet mounting tab is highly similar to inlet mounting tab  28  and is configured to axially receive a portion of a fastening device, such as a bolt (not shown). 
     Component side  32  is preferably configured to receive and maintain various sensing devices normally associated with industrial gas valves. For example, component side  32  may include a first area  72  for receiving a high pressure switch (not shown) and a second area  74  for receiving a low pressure switch (not shown). The pressure switches (or other devices) are simply affixed to the appropriate area  72 ,  74  so as to provide an indication of performance of valve  10 . Notably, an opposite side of valve body  12  may also be configured to receive and maintain auxiliary components. 
     Inlet O-ring  14  and outlet O-ring  16  are similar in construction, preferably made of a rubber material commonly used with gas flow sealing applications. Alternatively, other suitable elastomers may be used. Inlet O-ring  14  is preferably sized to surround inlet port  22 , and therefore has a diameter greater than that of inlet port  22 . Similarly, outlet O-ring  16  is sized to encircle or surround the outlet port (not shown). In one preferred embodiment, inlet port  18  and the outlet port have an identical diameter. However, while inlet O-ring  14  and outlet O-ring  16  are sized to surround the respective port, inlet O-ring  14  has a diameter different from that of outlet O-ring  16 . For example, in one preferred embodiment, inlet O-ring  14  has a diameter greater than a diameter of outlet O-ring  16 . Alternatively, inlet O-ring  14  may have a diameter less than that of outlet O-ring  16 . Notably, with this “reversed” configuration, sizing of the respective annular grooves (for example, annular groove  36 ) will change accordingly to correspondingly receive the respective O-ring. As described in greater detail below, by incorporating differently sized inlet O-ring  14  and outlet O-ring  16 , a dual seal is achieved when valve  10  is mounted to another, similarly constructed gas valve. 
     Assembly of valve  10  as part of a valve train  80  is shown in FIG.  2 . As a point of reference, valve train  80  includes valve  10 , a first pipe adapter  82 , a second valve  84 , a second pipe adapter  86  and various fastening devices  88 . First and second pipe adapters  82 ,  86  are identical and preferably include upper tabs  90  and a lower tab  91 . Each of tabs  90 ,  91  includes a bore  92  sized to receive a portion of one fastening device  88 . In a preferred embodiment, fastening device  88  includes a bolt  94 , a lock washer  96  and a nut  98 . Each bolt  94  includes a threaded shaft  100  extending from a bolt head  102 . It should be understood that fastening device  88  may assume a wide variety of other forms commonly known, and need not include lock washer  96 . 
     Second valve  84  is, in one preferred embodiment, identical to valve  10 . Therefore, relevant features of second valve  84  are described in general terms below. Second valve  84  includes a valve body  112 , an inlet O-ring  114  and an outlet O-ring  116 . Valve body  112  includes an inlet portion  118  and an outlet portion  120  (shown partially in FIG.  2 ). Inlet portion  118  forms an inlet port  122 ; whereas outlet portion  120  forms an outlet port (not shown). Upon final assembly, inlet O-ring  114  is sized to surround inlet port  118 . Similarly, outlet O-ring  116  is sized to surround the outlet port. To this end, inlet portion  118  includes an exterior face  134  forming an annular groove  136  for receiving inlet O-ring  114 . Similarly, outlet portion  20  includes an exterior face (not shown) forming an annular groove (not shown) for receiving outlet O-ring  116 . As with valve  10 , inlet O-ring  114  has a diameter different from that of outlet O-ring  116 . Thus, where second valve  84  is identical to one preferred embodiment of valve  10 , inlet O-ring  114  of second valve  84  is greater in diameter than outlet O-ring  116 . Further, inlet O-ring  114  of second valve  84  is substantially identical in diameter with inlet O-ring  14  of valve  10 . Similarly, outlet O-ring  116  of second valve  84  is substantially identical in diameter with outlet O-ring  16  of valve  10 . Finally, in one preferred embodiment, second valve  84  includes inlet coupling means  126 , an inlet mounting tab  128 , outlet coupling means  130  and an outlet mounting tab (not shown). 
     Generally, FIG. 2 depicts two inlet coupling means  126  located on opposite sides of inlet port  122 , each including an exterior surface  140  and a bearing surface  142 . A slot  144  extends between exterior surface  140  and bearing surface  142 . Further, a gap  146  is formed opposite bearing surface  142 . Outlet coupling means  130  includes a slot  160  extending between an exterior surface  162  and a base  164 . Slot  160  includes a first section  166  and a second section  168 . A bearing surface  169  is formed at the transition from first section  166  to second section  168 . 
     Assembly of valve train  80  in accordance with one preferred embodiment includes first assembling first pipe adapter  82  to inlet portion  18  of valve  10 . A grease, such as a general purpose lithium grease, is applied to annular groove  36 . Inlet O-ring  14  is inserted into annular groove  36 . Fastening devices  88  are used to couple first pipe adapter  82  to valve  10  (along with various other components of valve train  80 ). For purposes of clarity, reference to fastening device  88 , and in particular bolt  94 , lock washer  96  and nut  98 , will be made generally with reference to one fastening device  88 , it being understood, however, that multiple fastening devices  88  are employed throughout valve train  80 , several of which are shown in FIG.  2 . 
     In preferred arrangement, bolts  94  fitted with lock washers  96  are inserted through bores  92  associated with upper tabs  90  of first pipe adapter  82 . Nuts  98  are then secured onto the ends of threaded shafts  100  of the bolts. First pipe adapter  82  is maneuvered adjacent to inlet portion  18  of valve  10  such that threaded shafts  100  slide upwardly into slots  44  of opposing inlet coupling means  26 , respectively. When properly positioned, lock washer  96  and nut  98  are located within gap  46 . A third bolt  94  is inserted through bore  92  of lower tab  91  and bore  50  of inlet mounting tab  28 . A lock washer (not shown) and nut (not shown) are then secured over third bolt  94 . All three fastening devices  88  are then tightened. In this regard, it should be noted that inlet coupling means  26  facilitates access to nuts  98  by a tightening tool (such as a wrench) via gap  46 . Once tightened, inlet O-ring  14  provides a seal between inlet portion  18  and first pipe adapter  82 . 
     Valve  10  is assembled to second valve  84 . As shown in FIG. 2, valve  10  is mounted in a back-to-back relationship with second valve  84 . First, the annular groove (not shown) of outlet portion  20  and annular groove  136  of inlet portion  118  are greased. Outlet O-ring  16  is inserted into the annular groove associated with outlet portion  20  of first valve  10 . Similarly, inlet O-ring  114  is inserted into annular groove  136  of second valve  84 . Two bolts  94  are provided (one of which is shown in FIG.  2 ), each having a lock washer  96  coaxially disposed over threaded shaft  100 , abutting bolt head  102 . A separate nut  98  is threaded onto each threaded shaft  100 , positioned at an end opposite a respective bolt head  102 . Each separate nut  98  is inserted into a respective one slot  60  of outlet coupling means  30 , recalling that FIG. 2 depicts only one of two outlet coupling means  30 . In particular, for each outlet coupling means  30 , nut  98  is captured within second section  68  such that nut  98  abuts bearing surface  70 . Threaded shaft  100  extends from nut  98  through first section  66 . With both fastening devices  88  in place, second valve  84  is maneuvered toward valve  10  such that inlet portion  118  is adjacent, but slightly above, outlet portion  20 . Second valve  84  is then maneuvered downwardly such that bolts  94  slide into slots  144  associated with the respective inlet coupling means  126  of second valve  84 . A third bolt  94  (not specifically shown in FIG. 2) is extended through bore  150  of inlet mounting tab  128  and the opening in the outlet mounting tab (not shown) of outlet portion  20 , and secured with a lock washer  96  and nut  98 . All three fastening devices  88  are then tightened. In this regard, a single tool can be used to tighten fastening devices  88  associated with outlet coupling means  30  and inlet coupling means  126 . Outlet coupling means  30  captures nut  98 , limiting rotation thereof. Further, gap  146  in inlet coupling means  126  allows for access to bolt head  102  by a tool. 
     FIG. 3 depicts the relationship between outlet coupling means  30  and inlet coupling means  126  in greater detail. As is clear from FIG. 3, the configuration of outlet coupling means  30  and inlet coupling means  126  can be reversed such that inlet coupling means  126  captures nut  98 . Further, orientation of fastening device  88  may be reversed such that bolt head  102  is captured by outlet coupling means  30 . Finally, it should be understood that only one preferred embodiment of outlet coupling means  30  and inlet coupling means  126  has been provided. A wide variety of other structural configurations may be employed whereby a portion of fastening device  88  (for example, nut  98  or bolt head  102 ) is captured so as to limit rotation thereof. The other available structural configurations include, in most basic terms, a slot sized in accordance with an enlarged portion of the fastening device employed. The slot is accessible from at least one direction relative to the valve body (i.e., from above, below or a side) so that the relevant portion of the fastening device can readily be inserted or removed from the slot. 
     When assembled back-to-back, a dual seal is provided between valve  10  and second valve  84 . More particularly, as shown in FIG. 4, outlet O-ring  16  and inlet O-ring  114  each form an independent seal between outlet portion  20  and inlet portion  118 . For example, outlet O-ring  16  contacts and seals against exterior face  134  of second valve  84 , whereas inlet O-ring  114  contacts and seals against exterior face  104  of first valve  10 . Particularly, the dual seal configuration is achieved by incorporating differently-sized outlet O-ring  16  and inlet O-ring  114 . Importantly, O-rings  16 ,  114  are sized so as to not interfere with one another upon assembly. In other words, outlet O-ring  16  does not contact inlet O-ring  114 , and vice-versa. Instead, metal-to-metal contact is provided for each O-ring  16 ,  114 . 
     Returning to FIG. 2, second pipe adapter  86  is assembled to outlet portion  120  of second valve  84 . Annular groove (not shown) associated with outlet portion  120  is greased. Outlet O-ring  116  is placed within the annular groove. Nut  98  is placed within slot  160  associated with each outlet coupling means  130  (one of which is shown in FIG.  2 ). Once again, second section  168  is sized to capture nut  98 , limiting rotation thereof. Two bolts  94  (one of which is shown in FIG. 2) are provided, each having a lock washer  96  abutting a respective bolt head  102 , and passed through bores  92  in upper tabs  90  of second pipe adapter  86 . Second pipe adapter  86  is then maneuvered such that threaded shafts  100  of previously positioned bolts  94  threadably engage a respective nut  98 . A third bolt  94  (not specifically shown in FIG. 2) is passed through lower tab  91  and outlet mounting tab (not shown) of second valve  84 . All fastening devices  88  are then tightened. In this regard, outlet coupling means  130  facilitates rapid fastening by preventing rotation of nuts  98 . 
     During use, valve train  80  operates in accordance with the internal functional characteristics associated with valve  10  and second valve  84 . In this regard, while both valve  10  and second valve  84  are shown as being fluid power valves, any other gas valve type currently available, or in the future conceived, may be used for either valve  10  or second valve  84 . Thus, valve  10  and/or second valve  84  may alternatively be a diaphragm valve, a solenoid valve, a vent valve, a shut-off valve, a metering valve, a butterfly valve, etc. Notably, valve  10  need not be identical to second valve  84 . Preferably, however, each of valve  10  and second valve  84  includes corresponding inlet and outlet design characteristics to facilitate rapid, back-to-back series mounting. More particularly, each of valve  10  and second valve  84  includes an inlet O-ring and an outlet O-ring. The respective inlet O-rings are similarly sized; as are the respective outlet O-rings. However, the inlet O-rings have a diameter different from a diameter of the outlet O-rings such that when the valves  10 ,  84  are mounted back-to-back, a dual seal is achieved. Additionally, in one preferred embodiment, valve  10  and second valve  84  incorporate corresponding inlet and outlet coupling means. More particularly, one of either of the inlet coupling means or the outlet coupling means is configured to capture a portion of an associated fastening device so as to facilitate rapid mounting. 
     As described above, valves in accordance with the present invention are not limited to the fluid power valve design shown in the various figures. By incorporating the inventive features of the present invention, a variety of different valve types can be directly mounted in series. For example, FIG. 5 provides an exploded view of an alternative valve train  170 . Valve train  170  includes several elements previously described in detail, including first pipe adapter  82 , valve  10 , second valve  84  and second pipe adapter  86 . Details on these components are provided above, and like reference numerals are reflected in FIG.  5 . Additionally, valve train  170  includes valve adapter  172  configured to receive a vent valve (not shown). Valve adapter  172  includes an adapter body  171  defining an inlet portion  174 , an outlet portion  176 , inlet coupling means  178 , an inlet mounting tab  180 , an outlet coupling means  182 , an outlet mounting tab  184  and a valve connection port  185 . Inlet portion  174  is preferably integrally formed with inlet coupling means  178  and inlet mounting tab  180 , an defines an inlet port  186 . Similarly, outlet portion  176  is preferably integrally formed with outlet coupling means  182  and outlet mounting tab  184  and defines an outlet port (not shown). FIG. 5 depicts two inlet coupling means  178 , each comprising a radial extension  188  forming a passage  190 . Inlet mounting tab  180  similarly forms a passage  192 . FIG. 5 depicts two outlet coupling means  182 , formed at opposite sides of outlet port (not shown). In this regard, each outlet coupling means  182  includes a bore  194  extending between an exterior surface  196  and a bearing surface  198 . In this regard, a slot  200  is formed at bearing surface  198 . Slot  200  is sized to capture a portion of a fastening device  88 , such as nut  98  or bolt head  102 . Finally, outlet mounting tab  184  forms an axial passage (not shown). Finally, valve connection port  185  is interiorly threaded for fluid connection to a separate valve (not shown), such as a vent valve. 
     Assembly of valve train  170  is highly similar to that previously described for valve train  80  (FIG.  2 ). First pipe adapter  82  is assembled to valve  10  as previously described. Valve adapter  172  is then assembled to valve  10 . Outlet O-ring  16  is secured to outlet portion  20  so as to surround outlet port (not shown). Outlet portion  20  of valve  10  is mounted to inlet portion  174  of valve adapter  172  via three of fastening devices  88 . A nut  98  is placed into each of outlet coupling means  30  (one of which is shown in FIG. 5) of valve  10  such that nut  98  is captured within second section  68  of slot  60 . Two bolts  94  (one of which is shown in FIG.  5 ), each with a lock washer  96  coaxially positioned against a respective bolt head  102 , are inserted through passages  190  of inlet coupling means  178  and threaded to previously positioned nuts  98 , respectively. A third bolt  94  (not specifically shown in FIG. 5) is passed through the outlet mounting tab (not shown) and inlet mounting tab  180 , and secured with a lock washer  96  and nut  98 . All three fastening devices  88  are tightened. In this regard, placement of nuts  98  in second sections  68  of slot  60  limits rotation of nut  98 , thereby facilitating rapid fastening. 
     Valve adapter  172  is then assembled to second valve  84  by first inserting inlet O-ring  114  into annular groove  136 . Two bolts  94  (one of which is shown in FIG. 5) are then passed through bores  194  associated with each of outlet coupling means  182 . In this regard, slots  200  associated with outlet coupling means  182  receive and maintain a respective bolt head  102 , limiting rotation thereof. A lock washer  96  and a nut  98  are then placed over threaded shaft portion  100  of the previously positioned bolts  94 . Second valve  84  is then maneuvered adjacent to valve adapter  172  such that each of threaded shafts  100  slide into slot  144  associated with inlet coupling means  126 , respectively. A third bolt  94  (not specifically shown in FIG. 5) is passed through outlet mounting tab  184  and inlet mounting tab  128 , and receives a lock washer  96  and nut  98 . The three fastening devices  88  are then tightened so as to secure outlet portion  176  to inlet portion  118 . Once again, access to nuts  98  by a tool is facilitated by gap  146  associated with inlet coupling means  128 . Further, slots  200  associated with outlet coupling means  182  limit rotation of respective bolt heads  102 , thereby facilitating rapid assembly. 
     Finally, second pipe adapter  86  is assembled to second valve  84  in a manner previously described. 
     In the event a valve  10 , or  84 , or valve adapter  172  associated with valve train  170  malfunctions, a replacement can be rapidly installed. The above-described assembly procedure associated with a particular valve is simply reversed, that valve removed, and replaced with a new valve. Thus, unlike previous designs, it is unnecessary to remove and potentially replace various pipe nipples. Further, unlike an integrally casted, dual valve design, malfunction of one valve does not render the entire valve train scrap. 
     The gas flow control valve of the present invention provides a marked improvement over previously used designs. In particular, where code (or other certain design preferences) requires implementation of two valves mounted in series, the present invention facilitates direct, back-to-back assembly. In particular, a wide variety of different type valves can be provided, each having an inlet portion with an inlet O-ring of a first size and an outlet portion maintaining an outlet O-ring of a different size. When assembled back-to-back, the inlet O-ring and the outlet O-ring each form an independent seal between the two valve bodies. To this end, a sizing of the O-rings is specifically selected so that upon final assembly, the O-rings do not contact one another, but instead directly contact each of the respective valve bodies. Further, in accordance with one preferred embodiment of the present invention, each of the two valves includes a coupling means configured to facilitate rapid assembly and disassembly whereby a portion of a respective fastening device is prevented from rotating. Thus, the gas valve of the present invention provides for a valve train having readily interchangeable valves. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the present invention. For example, the gas valve has been described as having inlet coupling means configured to provide access to a fastening device and an outlet coupling means configured to limit rotation of a portion of the fastening device. However, these relationships can be reversed such that the inlet coupling means limits fastener rotation. Similarly, while each valve has been shown as incorporating three coupling means, any other number, either larger or smaller, is acceptable. Along these same lines, the described use of mounting tabs at both the inlet and outlet may be eliminated.