Abstract:
A manifold gauge assembly that combines in a single apparatus the features of a manifold gauge set and the features of a phase change device. The manifold gauge assembly may be utilized for charging both pure liquid refrigerants and blends of liquid refrigerants and still maintain the ability of full porting for vacuum optimization. The invention also comprises a phase change device adapted to be fixedly attached to a manifold.

Description:
This application claims the benefit pursuant to 35 U.S.C. §119(e) of Provisional U.S. patent application Serial No. 60/261,560 filed on Jan. 12, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to refrigeration systems, and more particularly, to a manifold gauge set assembly for use in charging a refrigerant into a refrigeration system at start-up or during a service condition. 
     Manifold gauge sets are utilized by air conditioning and refrigeration technicians to service and/or charge the equipment that comprises the air conditioning or refrigeration system. A manifold gauge set provides readout devices from which the operational (i.e., discharge and suction) pressures of the system can be determined, and provides one or more ports through which the technician can charge refrigerant from a storage cylinder into the system. 
     New air conditioning and refrigeration systems must be fully charged with refrigerant prior to first use of the system. In addition, existing systems from time to time require the addition of refrigerant to re-charge or top off a system due to the leakage of refrigerant from the system. When a refrigerant is to be charged into a refrigeration system, either as part of a new installation or as part of a service operation (top off), the refrigerant is typically charged into the system through a manifold gauge set. In a typical charging operation, the service technician pulls a vacuum through the gauge set on the system, and thereafter charges liquid refrigerant from the cylinder through the manifold gauge set and into the high side (also known as the liquid side) of the system. 
     As liquid refrigerant is charged into the system as part of a charging operation, the pressure in the high side gradually increases. If the pressure in the high side increases to an extent that it reaches the pressure inside the tank, the flow of liquid refrigerant ceases, and additional liquid refrigerant can no longer be introduced into the high side. In this event, the remaining portion of the refrigerant charge must be added to the low side (also known as the suction side) of the system in a vapor state. 
     It is well known in the refrigeration art that the removal of refrigerant vapor from a cylinder causes heat to be removed along with the vapor. As the temperature in the cylinder drops due to the removal of the heat with the vapor, the pressure in the cylinder also drops. As a consequence of this pressure drop, the rate of transfer of the vapor from the cylinder to the refrigeration system is reduced, ultimately to a point that the transfer becomes almost nonexistent. In order to increase the charge rate, and thereby more rapidly complete the charging operation, a service technician may attempt to circumvent the temperature/pressure loss in the cylinder by slowly introducing liquid (rather than vapor) from the cylinder into the low (suction) side of the system. Since the compressor can only compress low pressure vapor to high pressure vapor, the charging of liquid refrigerant into the low side can severely damage or even destroy the compressor. Such action can also result in harm to the technician due to the malfunction of the compressor. 
     The hazards associated with introducing liquid refrigerant directly into the low side of the compressor may be avoided when the technician utilizes a refrigerant phase change device. Applying Bernoulli&#39;s Principle (as the speed of a moving fluid increases, the pressure within the fluid decreases) to a volatile refrigerant allows for the expansion of the refrigerant with the drop in pressure and a change of state. Further application of the principle as described as the venturi effect is represented with different embodiments of the present invention. 
     Refrigerant phase change devices of this type are used to withdraw liquid refrigerant from the cylinder, rather than refrigerant vapor, for charging into the low side of the system. After being withdrawn from the cylinder, the liquid refrigerant passes through one or more pressure drop baffles, orifices or other restrictions in the phase change device, and is ultimately converted (flashed) to the vapor phase as it leaves the device and is charged into the low side of the system. 
     Since the early 1990&#39;s, in concert with the Montreal Protocol and the pending ban on CFC refrigerants, substitute or alternative refrigerants were developed to replace the refrigerants that were banned, or that were scheduled to be banned. With the exception of two single molecule refrigerants introduced for permanent inclusion in the industry, the remaining alternatives were classified as blends, which blends are zeotropic in nature. 
     Phase change devices as described are also utilized when the refrigerant composition to be charged into the system comprises a blend of refrigerants (i.e., a zeotrope), rather than a pure refrigerant. The individual components in a zeotrope boil, or change phase, at different temperatures, thereby causing the composition of the refrigerant blend to change at each component&#39;s respective boiling point. If a refrigerant composition comprising a blend of refrigerant components is charged into the system as a vapor, then the vapor will include an incorrect percentage of the various components of the liquid blend. In particular, the vapor charged into the system will generally comprise a higher percentage of the most volatile components than of the least volatile components. As a result, the true composition of the charged refrigerant will be altered from the intended composition, thereby hindering the charged system from performing as intended. 
     In addition, if refrigerant vapor enriched with one or more of the most volatile components is removed from the cylinder, the blend of refrigerants remaining in the cylinder will no longer include the proper percentages of each of the individual components. The use of the phase change device allows the technician to charge the refrigerant blend from the cylinder as a liquid, rather than as a vapor, thereby maintaining the proper percentages of the components of the refrigerant blend. Since multiple systems may be charged from a single cylinder of refrigerant, a cylinder having a compromised percentage composition could damage many systems and cause adverse economic consequences. 
     Although the benefits of using a phase change device are well known, the use of such devices can be inconvenient to a service technician. For example, as an initial matter, the device must be readily accessible to the technician, a feat that is not always accomplished when working at a remote site. The technician must then isolate the suction service access port, allowing removal of the suction side service hose from the manifold gauge set. This process will, as a result of this action, cause a slight expulsion of refrigerant trapped in the hose to the atmosphere as a consequence. The phase change device is installed at the suction hose connection port of the manifold gauge set, and the service hose is attached to the opposite side of the phase change device. The manifold gauge set suction side is opened allowing refrigerant to fill the hose, and the hose fitting is loosened at the system suction connection to purge any refrigerant and non-condensables to the atmosphere. 
     In an alternative arrangement, the center (or common) charging hose of the manifold gauge set is removed from the cylinder, resulting in the expulsion of refrigerant trapped in the hose to the atmosphere. The phase change device is secured to the refrigerant cylinder, and the center hose is attached to the phase change device. The cylinder valve is opened allowing refrigerant to fill the hose, and the hose fitting is loosened at the manifold gauge set to purge any refrigerant and non-condensable to the atmosphere. In the event the technician requires an unimpeded flow of refrigerant, then the process must be reversed to remove the phase change device from the cylinder. 
     The actions described above slow the operation, and require that the technician possess the proper equipment for introducing the device into the system. 
     It would be preferable if a charging operation could be carried out in a more efficient manner than is presently possible, by combining in a charging apparatus the benefits of a phase change device with the existing equipment of the system. Such a device should be sufficiently versatile such that a system evacuation (pulling a vacuum) and charging operation could be readily completed regardless of whether liquid refrigerant is being charged into the high or low side of the system, and without requiring the technician to connect or disconnect auxiliary devices after the charging operation has commenced and eliminate unnecessary multiple expulsions of refrigerant to the atmosphere. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the disadvantages present in charging operations by providing an improved manifold gauge assembly that combines in a single apparatus the features of a manifold gauge set and the features of a phase change device. Also included is an alternative phase change device that is adapted to be permanently affixed to an existing manifold gauge set to provide a device offering the same benefits as the integral apparatus. 
     The improved manifold gauge assembly may be utilized for charging both pure liquid refrigerants and blends of liquid refrigerants and still maintain the ability of full porting for vacuum optimization. Since the features of the manifold and the phase change device are combined, a technician may withdraw liquid refrigerant from a cylinder for charging into either the high side (as a liquid) or the low side (as a vapor resulting from phase conversion) of the system without the necessity of interrupting a charging operation for installation or elimination of equipment. The invention also comprises an improved phase change device adapted for fixed attachment with a manifold. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a manifold gauge set assembly according to a first embodiment of my invention. 
     FIG. 2 is a plan view of the embodiment of FIG. 1, with portions cut away and the gauges removed to show aspects of the phase change portion of the assembly, and with fluid passageways in the manifold block shown in broken lines. 
     FIG. 3 is a cross-sectional view of the manifold gauge assembly taken along  3 — 3  of FIG.  2 . 
     FIG. 4 is a perspective view of an alternative embodiment of a manifold gauge set according to the present invention. 
     FIG. 5 is a partially-sectioned view of the phase change portion of the present invention, with the stem in the closed position. 
     FIG. 6 is a partially-sectioned view similar to that of FIG. 5, with the stem in the open position. 
     FIGS. 7 and 8 illustrate a partially-sectioned representation of another embodiment of the present invention, for use with an existing manifold gauge. 
     FIGS. 9 and 10 illustrate an alternative embodiment of the phase change device that is incorporated into the manifold body. 
     FIG. 11 illustrates an alternative device that is fixedly attached to a conventional gauge set utilizing the phase change device of FIGS. 9 and 10. 
     FIG. 12 is an end view of the valve stem/seat phase change device FIGS. 9-11. 
     FIG. 13 is a cut-away view of the phase change device shown in FIGS. 9-11. 
     FIG. 14 is a plan view of another embodiment of the present invention with the gauges removed, and having an additional side valve access. 
     FIG. 15 is a front view of the embodiment of FIG.  14 . 
     FIG. 16 is a cut-away view of angle valve  117  shown in FIGS.  14  and  15 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A manifold gauge set assembly  10  according to an embodiment of the present invention is illustrated in FIGS. 1-3. The assembly includes a housing comprising a manifold block portion  12  and a projection  30 . The manifold block portion  12  includes conventional low and high side gauges  14 ,  16 , respectively. Connectors  18 ,  20 ,  22  are provided to attach to fluid transfer conduits, such as hoses, to establish fluid communication with a reservoir of a fluid, such as a refrigerant. Control devices, such as handles  24 ,  26  and  28 , are provided for controlling valves (not shown) for opening and closing fluid passageways within manifold block portion  12 , thereby establishing a route for transport of the fluid from the reservoir to its ultimate destination, such as a refrigeration or air conditioning system. Preferably, the housing is formed of conventional materials commonly used in the refrigeration industry, such as brass, anodized aluminum, steel, various composite materials and compatible elastomers. 
     As shown in FIG. 2, the phase change portion of manifold gauge assembly  10  is substantially housed within projection  30 , which is integrally formed with manifold block portion  12 . In the embodiment shown, projection  30  extends outwardly in generally perpendicular fashion from block portion  12 . A portion of the upper surface of assembly  10  is cut away and the gauges are removed in FIG. 2 to better illustrate details of the phase change feature of assembly  10 . Fluid passageways  32 ,  34  in manifold block portion  12  are shown in broken lines. As illustrated in the figures, handles  24 ,  26 ,  28  are spaced from respective block  12  and projection  30  of assembly  10  by hexagonal nuts  25 ,  27 ,  29 . FIG. 2 shows stem portion  36  and leading edge  38 . 
     FIG. 3 is a cross-sectional view taken along lines  3 — 3  of FIG.  2 . Stem portion  36  is rotatably connected to handle  26  via a threaded connection formed by complementary screw threads  40 ,  42 , in order to translate the rotation of handle  26  to axial movement of stem portion  36  and leading edge  38 . The internal elements in FIGS. 2 and 3 are shown with greater particularity and discussed in greater detail in connection with the discussion of FIGS. 5 and 6. 
     The embodiment of FIGS. 1-3 illustrates an arrangement wherein the phase change portion of assembly  10  is housed in a projection  30  that is integrally formed with manifold block portion  12 . Alternatively, the phase change portion of assembly  10  could be fully positioned within the main body of block portion  12 , thereby eliminating the portion  30  of assembly  10  that projects outwardly from block  12 . In this event, handle  26  would be spaced outwardly from the main body of block  12  substantially the same distance as handles  24 ,  28 . 
     In an alternative embodiment, the manifold block and the phase change device may initially be formed as separate components, and combined by conventional attachment methods to form a unitary structure. An example of such an arrangement comprises a conventional manifold block having a sight glass. In this arrangement, the phase change device could, for example, be fixedly attached by screwing or other means into the sight glass orifice to form a unitary structure. 
     FIG. 4 illustrates an embodiment wherein an existing manifold block is combined with a phase change device. This embodiment combines the features of a manifold and phase change device by fixedly attaching phase change device  50  to an existing manifold, such as the conventional manifold  52  shown in the figure. Connectors  54 ,  56 ,  58  are provided for attachment to fluid transfer conduits. The components of this assembly are fixedly combined to form a permanent charging apparatus, much in the same manner as the integral assembly of FIG.  1 . In this case, phase change device  50  includes connector  60  (FIGS. 5 and 6) on an upper surface thereof Connector  60  is attached to manifold  52  by conventional attachment means known to those skilled in the art, such as female coupling member  59  shown in FIG.  4 . 
     The operation of the manifold gauge assembly may be better understood with reference to FIGS. 5 and 6, which illustrate in greater detail portions of the inner workings of the phase change aspect of the device. Like elements are referred to by common reference numerals in all of the figures. The partially-sectioned views of the phase change device  50  shown in FIGS. 5 and 6 illustrate the internal workings of device  50 , which features are also common to the phase change aspect of the integral device shown in FIGS. 1-3. 
     In operation, phase change device  50  includes a restriction member that is press fit or otherwise fixed in place within the interior of device  50 . In the embodiments of FIGS. 1 and 4, restriction member comprises a conventional generally cylindrical barrel-shaped portion  64 . Although barrel-shaped restriction member  64  is shown in the figures, any configuration that is complementary to the configuration of the interior of device  50  to form a tight fit therewith and fulfills the purpose of the restriction member will suffice. The restriction member, or barrel portion  64 , is preferably formed of conventional materials such as brass, anodized aluminum, steel, composite materials, elastomers and combinations of the foregoing, although those of skill in the art will appreciate that other similarly-compatible materials may be substituted. 
     As shown in FIGS. 5 and 6, barrel  64  is positioned within device  50  such that chambers  66 ,  68  are defined on opposite sides of barrel  64 . Barrel  64  further includes a center port  70  (shown in broken lines) extending axially therethrough to establish communication between chambers  66 ,  68 . 
     In the embodiment shown, barrel  64  has two orifices extending along its outer surface to establish communication between chambers  66 ,  68 . In this embodiment, the orifices comprise two generally serpentine-shaped grooves  72 ,  74 . As shown in FIG. 2, serpentine grooves  72 ,  74  are machined or otherwise formed in the outer surface of barrel  64 , by conventional means known to those skilled in the art. Preferably, each groove is disposed on a separate one-half of the outer surface (measured longitudinally) of barrel  64 , and winds in repetitive serpentine fashion from the top of the device (with respect to the orientation of FIG. 1) to the bottom of the device and back. The partially-sectioned view of FIG. 3 illustrates (in broken lines) the serpentine groove  74  extending along the outer surface of one-half of barrel  64 . 
     Although the embodiment illustrated in the figures shows two complementary serpentine-shaped grooves, other numbers of grooves may alternatively be provided, as well as grooves having other shapes, configurations and positions on the outer surface of barrel  64 . For example, instead of the serpentine grooves that wind over respective longitudinal halves of the barrel as described, one or more helical grooves may be formed to wind completely around the outer surface of barrel  64  in helical fashion to provide communication between chambers  66 ,  68 . Alternatively, one or more axial grooves may be formed to simply extend longitudinally on said outer surface between chambers  66 ,  68 . 
     Those skilled in the art will recognize that stiff other configurations may be readily substituted for those specifically described. For example, due to the tight fit of the restriction member  64  in device  50 , the desired effects can be obtained if the grooves are machined or otherwise formed on the inner surface of device  50 , rather than on the outer surface of restriction member  64  as described. The use of an arrangement incorporating a plurality of grooves on the outer surface of barrel  64 , such as the serpentine arrangement described, is presently favored, however, as it allows more fluid to be transported through the grooves and subjected to the phase change operation than when a single groove is utilized, and the configuration may be readily machined by conventional means. In addition, this arrangement enables the technician to easily control the amount of fluid passing between the chambers. 
     Although it is preferred that port  70  extends axially through the center of barrel  64  as shown, those skilled in the art will recognize that other configurations that accomplish the same purpose of enabling passage of refrigerant in the liquid phase through the barrel may be substituted. For example, the port need not necessarily extend axially through the center of the barrel, and may be axially positioned elsewhere on the barrel, or even as a groove or cutout on the outer axial surface of the barrel. Such alternative configurations may be substituted, as long as suitable provision is made to provide a stopper or related closure mechanism to enable the technician to selectively open and close the larger diameter port (when compared to the diameter of the grooves) to liquid refrigerant. Port  70  must be dimensioned such that liquid refrigerant entering port from chamber  66  remains in the liquid phase as it exits the port  70  and occupies chamber  68 . Those skilled in the art will be readily able to dimension port  70  to have a large enough diameter such that the liquid refrigerant is not flashed to vapor as it passes therethrough. The exact dimensions are generally not critical as long as this objective is met. 
     The amount of fluid transported through the grooves may be controlled to a certain extent by the selection of the size, shape and number of grooves. However, those skilled in the art will appreciate that the cross-sectional area occupied by the groove(s) and the rate of fluid transport must be controlled in a manner such that the phase change benefits may be realized, or on other word that the liquid is flashed to a vapor, m accordance with known principles utilized in prior art phase change devices. This necessitates that consideration is given to the volume, density, pressure and temperature of all refrigerants used with the inventive manifold gauge assembly. Since the effect of the phase change is also a means of refrigerant flow control, the selection of the diameter, shape, equivalent length, and number of grooves (or the selection of the orifice size in the design of FIGS. 7 and 8) must be controlled in order to prevent compressor overload. Additional embodiments of the means of phase change can also include machined orifices and/or turbines that further capitalize on the venturi effects created with the change in velocity and pressure. 
     The manifold gauge set may be operated in the following manner. A hose (not shown) is connected at one end to connector  56  and at the other end to a cylinder or tank of refrigerant (not shown). Initially, handle  26  is rotated such that stem  36  and leading edge  38  are in the “open” position shown in FIG. 6. A release valve on the refrigerant cylinder is opened to allow liquid refrigerant that is maintained under pressure in the cylinder to escape through the hose via port  62  into chamber  66 . As the liquid refrigerant enters chamber  66 , the refrigerant flows through large diameter (relative to the diameter of the serpentine grooves) center port  70  to chamber  68  on the opposing side of barrel  64 . The resistance offered by larger diameter center port  70  is less than that offered by the smaller diameter serpentine groove pathways  72 ,  74  on the outer surface of barrel  64 , and therefore the fluid passes through port  70  as the path of least resistance. Center port  70  may, for example, have an inner diameter of 0.25 inch (0.64 cm), and serpentine grooves  72 ,  74  may each have a diameter, for example, of 0.03 inch (0.08 cm). 
     Thus, as stated, the refrigerant passes from chamber  66  to  68  through the center port. Subsequently, the pressure present in chamber  68  is greater than the pressure exhibited on the leaving end (at the chamber  68 ) of serpentine grooves  72 ,  74 , thereby preventing fluid backflow into the grooves  72 ,  74 . Chamber  68  is in fluid communication with the fluid passageways in the manifold, such that the liquid refrigerant is selectively directed by opening valves  24  or  28 , which connect pathways  32  and  34 , respectively, into the low side or the high side of the system. Generally, when chambers  66 ,  68  are in communication via center port  70 , the liquid is directed into the high side. 
     When it is desired to charge into the low side, handle  26  is rotated such that stem  36  and leading edge  38  are advanced axially to the “closed” position. This position is shown in FIG.  5 . In this arrangement, stem leading edge  38  seals off center port  70 , thereby preventing refrigerant from flowing to chamber  68  from chamber  66  by way of port  70 , as described above. Serpentine grooves  72 ,  74  on barrel  64  are now dominant, and the liquid entering chamber  66  now passes through grooves  72 ,  74 . The restriction created reduces the pressure and volume, such that as the liquid enters chamber  68  it will expand at the reduced pressure and “flash” (change state) from liquid to saturated vapor, in a manner well known to those skilled in the art. With valve  24  open, the saturated vapor passes through pathway  32  and port  54  (or  18  in the embodiment of FIG. 1) to the low side of the system. 
     In addition to the arrangements described above, still other arrangements may be utilized, and are within the scope of the invention. For example, rather than utilizing a barrel having grooves on an outer surface thereof as described previously, the liquid refrigerant can be flashed to a vapor utilizing a valve and porting device as shown in the embodiments of FIGS. 7 and 8. 
     FIGS. 7 and 8 show a partially-sectioned representation of a free-standing device  80  for the field adaptation of an existing manifold gauge to convert it to a unitary device for the previously described benefits and advantages. Although the device of FIGS. 7 and 8 is designed for fixed attachment to an existing manifold gauge, with minor adaptation this device could alternatively be manufactured with an otherwise conventional gauge as an integral manifold gauge set assembly. 
     Referring now to the device of FIGS. 7 and 8, liquid refrigerant enters at port  85  from an external source and follows pathway  90  to inner chamber  94 . By turning handle  82  in a first direction, depressor pin  83  breaks contact with tapered seat  86 , to allow control spring  87  to press tapered seat  86  into port seat  93 , thereby closing pathway  95  and opening port seat  89  to pathway  91 . Liquid refrigerant in chamber  94  passes through port seat  89  into pathway  91 , and into the existing manifold gauge set via connection  92 . With this arrangement, the liquid refrigerant is directed internally in the gauge set to the high side of the system in the manner described in the previous embodiments. 
     Upon rotating control handle  82  in a second direction, depressor pin  83  contacts tapered seat  86  and depresses control spring  87 , thereby closing port seat  89  and opening port seat  93 . With seat  93  in the open position, liquid refrigerant travels through pathway  95  and enters restricted-diameter orifice port  88 . Port  88  is dimensioned in accordance with refrigerant density, volume, pressure and temperature in the same manner as the grooves in the previous embodiments, thereby creating the pressure drop and resulting in expansion of liquid refrigerant to saturated vapor in pathway  91  and into the manifold gauge set connection via port  92 . The vapor refrigerant is directed internally in the gauge set to the low side of the system as previously described. Pathway  91  and restricted-diameter port  88  may, for example, have the relative diameters of the embodiments of FIGS. 1-6, namely about 0.25 inch (0.64 cm) and about 0.03 inch (0.08 cm), respectively. 
     FIGS. 9 and 10 illustrate yet another embodiment of a phase change device that is incorporated into a manifold body to form an integral assembly. FIG. 11 illustrates an embodiment operationally similar to that of FIGS. 9 and 10, but that is intended to be fixedly attached to a conventional manifold gauge set. FIGS. 12 and 13 show additional operational details of these embodiments. 
     In these embodiments, the refrigerant is flashed by means of porting from a larger internal diameter to a smaller internal diameter. Liquid refrigerant enters via port  112  and travels through pathway  113  to chamber  114 . By rotating valve/valve stem assembly  115  in a first direction, the liquid refrigerant passes substantially unimpeded to center port  116  as before. By rotating assembly  115  in a second direction, center port  116  is closed off at machined seat  105 . The refrigerant is forced through the side(s) of valve stem seat  100  at ports  109 , and via internal pathway  101  to center port  102 , from which point the liquid refrigerant passes through a tapered path from small internal diameter to larger internal diameter. 
     Center port  116  and seat  105  on the refrigerant entering side may include refrigerant compatible seating material for accommodating and sealing with the corresponding valve stem seat/phase change device  100 . This configuration can be easily adapted to the independent device designed for the field purchased manifold gauge set  107  represented in FIG. 11 by way of attachment port  111 . 
     This embodiment can also include a device  103  to act as a balanced restriction that, by means of the venturi effect, offers an additional pressure drop and increased friction to enhance the pressure drop effects. The manifold gauge set body has a center bore pathway  116  with a machined seat  105  on the refrigerant entering side that may include refrigerant compatible seating material for accommodating and sealing with the corresponding valve stem seat/phase change device  100 . This configuration can be easily adapted to the independent device designed for the field purchased manifold gauge set device  107  represented in FIG.  11 . 
     Device  107  is permanently attached to a field purchased manifold gauge set at fitting  111 . The refrigerant enters at fitting  110  and follows the pathways described above. FIG. 12 shows an end view of the valve seat/phase change device  100 , identifying the possible port locations at  109 . FIG. 13 shows a cut view of valve seat/phase change device  100 , further illustrating entry ports  109  and connector hole  108 , to attach device  100  to valve stem  106 . 
     Another embodiment of the device of the present invention is shown in FIGS. 14-16. This embodiment includes internal components and functions as described previously, and an additional access valve  117 . Valve  117  is located in the center porting  116 , thereby allowing communication between valve  117  and all porting intersecting center port  116 . FIG. 15 is a front view with valve  117  illustrated in concert with center porting  116 . FIG. 16 shows a cut-away view of valve  117 . 
     When not otherwise specified herein, the selection of particular materials for the manufacture and assembly of the manifold gauge set assembly is well within the knowledge of those skilled in the art. Generally, it is expected that the assemblies, purchased parts and other components will comply with and satisfy the applicable industry codes and standards, e.g., SAE, U.L., etc. 
     While this invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention. Those skilled in the art may recognize or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described specifically herein, which equivalents are intended to be encompassed in the scope of the invention.