Patent Publication Number: US-6910510-B2

Title: Portable, cryogenic gas delivery apparatus

Description:
BACKGROUND TO THE INVENTION 
   Patients often wish to remain mobile or ambulatory while also receiving oxygen. This generally requires the oxygen delivery apparatus to be portable. To be portable, the oxygen or gas delivery apparatus preferably has to be compact and relatively lightweight. This is especially important since many patients needing oxygen are already frail or of limited physical capacity. One approach to such portability has been to store the oxygen or gas under pressure in gas cylinders, and such gas cylinders are equipped with pressure regulators, flow meters, and other apparatus for delivering the desired flow of oxygen to the patient. The need to make such high pressure gas cylinders smaller for ambulatory uses has meant a corresponding increase in the pressures applied to gases in such cylinders. The transportation and use of such high-pressure devices may require special handling in ambulatory or home-based settings. 
   Furthermore, even when gas has been compressed to 2,000 PSI, the compact cylinders need to be changed relatively frequently. This reduces the “range” that a patient may have with this high-pressure gas cylinder type of apparatus. 
   To lengthen the effective life of an oxygen delivery apparatus, manufacturers have resorted to so-called “cryogenic systems” or “liquid systems.” These systems make use of liquid oxygen as opposed to merely using pressurized oxygen in the gas phase. Liquid oxygen is generally 860 times more compact than typical pressurized gas. Cryogenic systems generally involve a thermal flask or cryogenic chamber. Such flasks or chambers include an inner vessel containing liquid oxygen. This inner vessel is surrounded by an outer casing and, importantly, between the outer casing and inner vessel, a vacuum is generally established to improve the insulative properties of the thermal flask. 
   In operation, cryogenic systems of the current art usually draw off a predetermined quantity of liquid oxygen which is then sent through a series of warming coils. As the liquid oxygen travels through the warning coils, it changes phase and evaporates into oxygen gas. The warming coils thus are often critical to transforming the liquid oxygen drawn from the flask into oxygen gas at an appropriate temperature to be inhaled by the patient. 
   Unfortunately, the systems of the current art suffer from various drawbacks and disadvantages. For example, the warming coils used in current systems have various difficulties, complexities, and other shortcomings. Coils often are bulky. Warming-coil-type apparatus may, under certain circumstances, be mishandled or otherwise operated imprudently with the result that liquid oxygen from inside the container is depleted too quickly or escapes inadvertently to potentially “burn” the users. 
   SUMMARY OF THE INVENTION 
   According to one aspect of the invention, a cryogenic gas delivery apparatus includes a chamber which is sufficiently insulated to maintain a cryogenic material as both a liquid and its corresponding gas. At least one probe has a first part positioned so that it is exposed to the pressure and temperature of the cryogenic material contained therein. A second part of the probe is located so that it is exposed to ambient temperature. In this way, the probe introduces heat from the ambient into the chamber. The probe is mounted to move relative to the chamber in response to variations in the pressure of the gas in the chamber. The movement of the probe correspondingly varies the amount of thermal energy which is introduced in the chamber. A passage leads from the gas in the chamber to deliver the gas to a user. 
   In another version of the invention, the foregoing gas delivery apparatus makes use of a conserver which receives the gas escaping from the chamber through the passage described above. The conserver, in turn, has a sensing system which is operatively connected to discharge gas at appropriate times through an outlet. In particular, the operative connection of the sensing system delivers gas when the sensing system senses inhalation by the user. 
   In still another version of the present invention, the system includes a fill system which is configured so that the chamber is only partially filled with cryogenic liquid. The remainder of the container is filled with the volume of the corresponding pressurized gas, forming a head space above the volume of the liquid phase. 
   According to another aspect of the present invention, a portable, liquid oxygen system delivers oxygen gas to a user. The portable liquid oxygen system includes a container for holding liquid oxygen and oxygen gas and an associated fill system, as well as a delivery system connected to the volume of oxygen gas in the container. The portable liquid oxygen system has a regulator, which operates on thermo-pneumatic principles in the sense that it varies the amount of thermal energy introduced into the container of the system in response to corresponding variations in the pressure of the gas volume within the container. The regulator includes a detection mechanism and a thermal transfer mechanism. The detection mechanism detects variations in the pressure of the volume of the oxygen gas, while the thermal transfer mechanism increases the evaporation rate of the liquid oxygen in the container in response to the detection of a predetermined drop in pressure, and decreases the evaporation rate in response to detecting an increase in pressure. As such, the regulator regulates the pressure of the volume of the oxygen gas and keeps it within a baseline pressure range. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
       FIG. 1  is a schematic of a cryogenic gas delivery apparatus according to one aspect of the present invention; 
       FIG. 2  is a cross-sectional, elevation view of one preferred embodiment of the cryogenic gas delivery apparatus of  FIG. 1 ; 
       FIG. 3  is an exploded perspective view of the embodiment shown in  FIG. 2 ; 
       FIG. 4  is a cross-sectional view taken along line IV—IV of  FIG. 3 ; and 
       FIG. 5  is an enlarged, cross-sectional view taken along line V—V of  FIG. 4 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to the drawings, a cryogenic gas delivery apparatus, preferably in the form of a portable, liquid oxygen system  21 , is shown schematically in  FIG. 1 . Liquid oxygen system  21  includes a vessel for holding material in a cryogenic state, preferably in the form of an insulated container  23  with a chamber  25  located therein. Chamber  25  is sufficiently insulated from the temperature and pressure of the ambient to hold oxygen in both the liquid and gaseous phases at temperatures below ambient temperature and pressures above ambient pressure. System  21  is “charged” with oxygen by means of fill system  23 . Fill system  27  includes one or more structures, components, or passages suitable for filling container  23  only partly with liquid oxygen. In this manner, chamber  25  contains not only a volume  29  of liquid oxygen therein, but also a volume  31  of pressurized oxygen gas located adjacent the volume of liquid oxygen. 
   Liquid oxygen system  21  preferably includes a delivery system  35 . Delivery system  35  includes one or more structures, components, or passages suitable for carrying gaseous oxygen from container  23  to the user. Preferably, delivery system  35  includes a flow-rate controller  37  and a conserver  43  in communication with the controller  37 . Flow-rate controller  37  receives gaseous oxygen from container  23  and restricts the flow therefrom by passing the gaseous oxygen through a user-selected one of a series of variably sized orifices  39 . The gaseous oxygen to be delivered to the user exits flow rate controller  37  and enters conserver  43 . 
   A pressure regulator  33  has been devised for liquid oxygen system  21  to regulate the pressure of the volume of pressurized oxygen  31  to remain within a selected base-line pressure range. The regulator  33  preferably operates on “thermo-pneumatic” principles, because, as detailed herein, it regulates the pressure of gas volume  31  by varying the amount of thermal energy introduced into chamber  25  in response to corresponding variations in the pressure of gas volume  31  in the chamber  25 . The regulator  33  maintains suitable pressures in gas volume  31  sufficient to supply delivery system  35  with oxygen to satisfy the user&#39;s breathing needs in a variety of sedentary and active circumstances. 
   Conserver  43  prolongs the “range” of the resulting portable, liquid oxygen system  21 , thereby increasing the freedom of those required to move about with the assistance of oxygen. Conserver  43  can be of any suitable type, including electronic, pneumatic, or a hybrid. In the illustrated embodiment, conserver  43  is preferably of the purely pneumatic-type. Gaseous oxygen to be delivered to the user enters conserver  43  and fills reservoir  41 . Conserver  43  includes a sensing system  45  with suitable structures, including two diaphragms  49 ,  50 , for opening reservoir  41  in response to inhalation by the patient. Oxygen is delivered from reservoir  41  to a patient through gas line  47  in response to the patient inhaling or inspiring. 
   Referring more generally to all the drawings, including  FIGS. 1–3 , regulator  33  preferably makes use of a transfer mechanism for thermal energy or heat, preferably in the form of a moveable probe  51  formed of heat conductive material. Probe  51  has a first portion  53  exposed to the pressure and temperature of chamber  25 . Preferably, first portion  53  is not only exposed to the pressure and temperature of chamber  25 , but is also physically positioned within chamber  25 . A second portion  55  of probe  51  is connected to first portion  53 , but is exposed to the ambient temperature, which, of course, is higher than the temperature in chamber  25 . Preferably, second portion  55  is not just exposed to the ambient, but also has a portion extending outside of container  23 . In this way, moveable probe  51  introduces heat from ambient  24  into chamber  25 . The introduction of heat into chamber  25  affects the evaporation rate characteristic of cryogenic chamber  25 , resulting in the liquid oxygen “boiling off” at a certain number of liters per minute. 
   Probe  51  is mounted to move relative to chamber  25  in response to variations in pressure in gas volume  31  within chamber  25 . In particular, probe  51  includes inner surface  57  extending outwardly from the central axis of probe  51  and thereby defining a surface area exposed to the pressure of volume  31  of the oxygen gas. The exposure of inner surface  57  to the pressure of volume  31  need not be direct, but can occur indirectly, such as through a flexible membrane, diaphragm, or seal, such as seal  111 . In this way, the pressure on inner surface  57  creates a force biasing probe  51  away from volume  31  of the gas in the direction indicated by the arrow A. 
   An opposing force is created by a biasing mechanism  61 , preferably in the form of spring  63 . Spring  63  is positioned to urge probe  51  toward the inside of chamber  25 , that is, toward volume  31  of pressurized oxygen, preferably in a direction indicated by the arrow B. The direction of arrow B is generally opposite the direction of the force acting on inner surface  57  of probe  51 . Thus, probe  51  moves relatively outwardly from chamber  25  in response to increasing pressure and relatively inwardly in response to decreasing pressure. 
   Spring  63  is shown as a coil-type spring coaxially received around the elongated portion of probe  51 . Other types and locations of springs are likewise suitable, and other types of biasing mechanisms  61  are also suitable. 
   The balance of inward and outward forces can be tailored to the particular needs and configuration of the system  21 . Preferably, the displacement of probe  51  into and out of chamber  25  is selected to alter the evaporation or “boil off” rate characteristic of the cryogenic system and to maintain the pressure of gas volume  31  at a corresponding pressure, plus or minus certain pressure variations. 
   The area of inner surface  57  and the characteristics of spring  63  are selected so that force on inner surface  57  moves probe  51  in the direction of arrow A when the pressure of volume  31  exceeds a predetermined upper threshold. The predetermined threshold is preferably any pressure which allows system  21  to delivery appropriate but not excessive amounts and rates of gaseous oxygen during operation. The movement of probe  51  outwardly from volume  31  of gas causes probe  51  to transfer less thermal energy to chamber  25 . Conversely, biasing mechanism  61  moves probe  51  inwardly into volume  31  when the pressure falls below a lower threshold. In so doing, probe  51  transfers more thermal energy to the container. Once the pressure of gas volume  31  has passed the upper or lower threshold, the amount which probe  51  moves depends on the amount by which the pressure has exceeded the upper threshold, or fallen below the lower threshold. 
   The inner surface  57  of probe  51  thus serves as a detection mechanism which detects variations in the pressure of gas volume  31 , and probe  51  thereby serves as a thermal transfer mechanism which either (1) increases the evaporation rate in response to the detection of a drop in pressure of volume  31 , or (2) decreases the evaporation rate in response to the detection of an increase in pressure of volume  31 . The movement of probe  51 , when pressures of the gas volume pass the upper or lower threshold pressures, thus permits regulator  33  to regulate the pressure of volume  31  to remain generally at a given pressure or within a given pressure range between the upper and lower thresholds. 
   Regulator  33  preferably includes a second probe  65  secured and located within chamber  25  with one end oriented toward concave bottom  109  of chamber  25 . Probe  65  terminates in a tip with a second probe surface  67  opposing a corresponding tip  66  of moveable probe  51 . The tip  66  of variable probe  51  thus moves toward or away from the opposing surface  67  of probe  65 . In this way, the heat present in the ambient is transferred from the outer, second portion  55  of probe  51 , down through first portion  53 , into probe  65 , and into the volume  29  of liquid oxygen, such heat transfer or temperature gradient being shown schematically by arrows C ( FIG. 1 ). 
   Heat transfer increases significantly when the opposing tips of probes  51 ,  65  contact each other, and conversely, heat transfer decreases significantly when such contact is substantially broken. Accordingly, in one preferred embodiment, the balance of inward and outward forces on the regulator  33  is tailored so that the moveable probe  51  simply moves into and out of contact with probe  65 . In such embodiment, the relatively smaller decreases or increases in heat transfer, as probe  51  moves from a first, out-of-contact position with probe  65 , to a second, out-of-contact position, are not as significant to regulating heat transfer and pressure. Instead, the probe movements into and out of contact maintain sufficient heat transfer and pressure in the system to deliver gaseous oxygen. 
   In the illustrated embodiment, liquid system  21  is substantially cylindrical or bullet-shaped and has first and second opposite ends  87 ,  91 . A base  89  is defined at end  87 . The liquid oxygen system  21  has a head  93  located at end  91 . Longitudinal axis  85  ( FIG. 3 ) extends between ends  87 ,  91 . Probe  51  is mounted to slide longitudinally relative to container  23 . As best seen in  FIG. 2 , probe  51  preferably comprises an elongated member with a head portion  56  having outer surface  59  and inner surface  57  both located proximate to upper surface  94  of head  93 . 
   Seal  111  is disposed along inner surface  57  of head portion  56 . Seal  111  is seated against both head  93  at the seal&#39;s outside perimeter and against probe  51  at its inner perimeter. Seal  111  thus forms part of the boundary between the pressures on its inner side exposed to chamber  25  and the pressure of ambient  24  on its opposite side. 
   Probe  51  has a shaft or elongated portion extending from head portion  56  through seal  111 . The shaft extends into and terminates in volume  31  of the gas. The shaft or elongated portion of probe  51  includes suitable structures so that biasing spring  63  is coaxially received thereon and held in a tensioned state. 
   Head  93  of system  21  includes a manifold  113  with a series of chambers, cavities, openings, and passages suitably located to interconnect the various systems and components of system  21 . With regard to probe  51 , the elongated portion of probe  51  extends through a manifold chamber  115  defined by an inner wall of manifold  113 . The elongated portion of probe  51  extends out of manifold chamber  115  and into a neck  117 , leading to chamber  25 . 
   Neck  117  includes suitable structures and features to keep probes  51  and  65  sufficiently aligned to operate as required to both transfer thermal energy and regulate the pressure of the volume of gas  31 . Preferably, neck  117  includes an alignment piece  119  received therein. Alignment piece  119  has a bore extending longitudinally therethrough, the bore terminating in opposite openings. Moveable probe  51  extends at least partly into the bore through one of the openings, the tip of moveable probe  51  being positioned at a medial location within the bore. Probe  65  enters through the opposite opening of alignment piece  119  and has its tip extend to a medial location within the bore proximate to the tip of probe  51 . In this way, the respective tips of probes  51  and  65  are opposing each other and substantially aligned, extending into alignment piece  119  from respective, opposite ends. 
   Manifold chamber  115  is suitably sealed from the ambient to experience the pressure associated with gas volume  31  during operation of apparatus or system  21 . Accordingly, the inner surface of seal  111  and the corresponding inner surface  57  of probe  51  are exposed to the pressures of gas volume  31 , and result in the outwardly directed force in the direction of the arrow A, discussed previously, acting to oppose the spring biasing force caused by spring  63  on moveable probe  51 . Thus, under the appropriate pressure conditions discussed previously, moveable probe  51  slides outwardly relative to alignment piece  119 , increasing the distance between the opposing tips of probes  51 ,  65 . 
   Probes  51 ,  65  preferably have their respective, opposing tips or surfaces contoured to increase the respective, mating surface areas of such tips and thus increase the thermal transfer between the opposing tips. Although the tip of variable probe  51  is generally concave and the corresponding tip of probe  65  is convex, any other contour is likewise suitable, so long as the desired amount of thermal transfer occurs. In fact, although probes  51 ,  65  are preferably elongated and are shown to terminate in tips, it is understood that the probes need not be elongated, and need not end in tips; other shapes and configurations are suitable and can be designed to effectively transfer thermal energy and regulate the pressure of gas in system  21 . 
   When probe  51  moves longitudinally, head portion  56  likewise is displaced longitudinally. A cavity  121  is defined in head  93  for receiving head portion  56  of probe  51  when it moves outwardly, and cavity  121  is sufficiently deep to accommodate the full range of motion of probe  51  which occurs during operation of regulator  33 . 
   Referring more particularly to  FIG. 4 , fill system  27  is used to fill or charge system  21  with liquid oxygen. Fill system  27  includes fill chuck  69  structured to connect to a source  22  of oxygen in the liquid phase. In this case, source  22  comprises a base liquid oxygen unit. Fill chuck  69  is, in turn, in thermal connection to fill tube  71 , which extends from fill chuck  69  into chamber  25  and terminates in an opening approximately in the middle of chamber  25 . 
   Chamber  25  includes suitable vents, one of which is shown schematically at  73  in  FIG. 1 , for “blowing off” excess oxygen. Vent  73  (when open) is in communication with chamber  25  and fill system  27 . The vent  73  and fill system  27  are configured so that chamber  25  becomes only partially filled, preferably about 50%, with liquid oxygen by operation of fill system  27 . This assures that both the volume  29  of liquid oxygen and the volume  31  of gaseous oxygen are formed upon filling or charging the system  21 . 
   Fill chuck  69  makes use of a poppet valve  97 , in which poppet spring  101  biases poppet pin  99  and poppet seal  103  outwardly to seat and seal against annular seat  105 . During the filling operation, mating outlet or nozzle  107  of base unit  22  unseats or unseals poppet valve  97  by urging it radially inwardly when nozzle  107  is inserted into fill chuck  69 , in a known manner. A flow path for oxygen in liquid form is thus defined from the pressurized source in base unit  22 , through nozzle  107  to exit base unit  22 , into and through fill chuck  69  and fill tube  71 , and into chamber  25 . 
   Fill chuck  69  extends transversely and inwardly from the circumferential sidewall  123  of manifold  113 , terminating at a central location at or proximate to manifold chamber  115 . At this central location, the outer or upper end of fill tube  71  extends orthogonally from fill chuck  69 , extending longitudinally into chamber  25 . Although fill chuck  69  and fill tube  71  preferably join each other at a central location within manifold  113 , the flow path defined by these elements is preferably not in fluid or pneumatic communication with manifold chamber  115  but remains insulated therefrom by suitable walls. 
   Fill chuck  69  is secured within a cavity of manifold  113  with suitable structures so that fill chuck  69  is substantially insulated from thermal contact with manifold  113  by insulated space  125 . Insulated space  125  extends between the cylindrical sidewall of fill chuck  69  and the corresponding inner wall of manifold  113 , over substantially all of the length of fill chuck  69 . In this way, liquid oxygen passing through fill chuck  69  absorbs minimal heat from the manifold  113  by virtue of the insulated space  125  therebetween. 
   A trapping mechanism  127 , best seen in  FIGS. 2 and 5 , reduces leakage of the liquid phase out of the container which would otherwise occur during filling of the container from approximately 40% to 50% of its capacity. As best seen in  FIG. 5 , trapping mechanism  127  includes a set of wings  129  which extend from alignment piece  119  radially outwardly to abut the inner cylindrical wall of neck  117 . By virtue of this structure, it will be appreciated that when the portable liquid oxygen apparatus  21  is turned on its side for filling as shown in  FIG. 4 , once the level of liquid oxygen reaches the lower wall portion  131  of neck  117 , further rising of the level of liquid oxygen in volume  29  is impeded from flowing out neck  117  by wings  129 . Wings  129  thus act as a dam to keep liquid oxygen from flowing into manifold chamber  115  and potentially boiling off and out the various relief valves provided in apparatus  21 . 
   Although fill system  29  includes a trapping mechanism  127  to avoid the inadvertent release or entrainment of liquid oxygen during filling, once the level of liquid oxygen passes the upper edge  133  of wings  129 , the liquid oxygen is free to flow past wings  129 , out neck  117 , and into manifold chamber  115 . Once in manifold chamber  115 , the contact of liquid oxygen with manifold  113  generally introduces sufficient heat energy to entrain or partly evaporate such liquid oxygen out of system  21 . Manifold chamber  115  is in pneumatic communication with one or more relief valves or vents to atmosphere, including vent  73 . As such, if the user continues to try to fill liquid oxygen system  21  beyond the approximately 50% fill level, liquid oxygen will flow back up neck  117  and be vented out of the system. This maintains chamber  25  only about 50% filled with a volume  29  of liquid oxygen and the remainder filled with a gas volume  31  of pressurized oxygen. The partial filling of chamber  25  thus forms a “head space” of pressurized oxygen above the volume  29  of liquid oxygen, and it is this head space of pressurized oxygen which is drawn upon to meet the user&#39;s breathing needs, as explained subsequently. 
   Vent  73  preferably comprises a vent-to-atmosphere with a passage extending generally transversely from manifold chamber  115  outwardly to terminate at the atmosphere at a suitable location on sidewall  123  of manifold  113  ( FIGS. 2–3 ). Vent to atmosphere  73  includes handle  135  with a cam at its end. When handle  135  is pulled outwardly by the user, a flow path is opened between manifold chamber  115  and the atmosphere. The flow path vents excess liquid oxygen with which a user may attempt to charge the system after it has been filled to the approximately 50% capacity preferable for this invention. This flow path likewise allows gas to escape chamber  25  during operation of fill system  27  to charge apparatus  21  with liquid oxygen. 
   Flow rate controller  37 , vent-to-fill valve  73 , fill chuck  69 , and nozzle  179  are secured to head  93  at respective angular locations thereon, and are located to be accessible by the user from the circumferential sidewall  123  of head  93 . 
   Fill tube  71  and fill chuck  69  include cylindrical walls which are preferably made as thin as structurally possible, and preferably of a material with a very low thermal conductivity. In this way, the fill system emits a very low amount of heat energy or BTUs to the liquid oxygen as it passes through fill system  27 , promoting more efficient filling of system  21 . 
   Insulated container  23  is preferably a double-wall container, that is, one having an inner wall  139  which defines chamber  25  therein, and an outer wall  141  which extends in spaced relation to inner wall  139  to define in insulating region  143  between the inner and outer walls  139 ,  141 . To improve the insulative characteristics of insulating region  143 , it is generally evacuated of air to form a vacuum. Outer wall  141  includes an end portion  145 . End portion  145  has a flange or mounting bezel  147  secured thereto at a central location. Flange  147  is configured so that head  93  can be secured to it, thus securing the various components of head  93  in operative relation to the container  23 . Flange  147  is preferably annular and defines a flange opening  149  leading into chamber  25  which allows fluid communication between manifold chamber  115  in head  93  and chamber  25  of container  23 . 
   Neck  117  is preferably defined by a cylindrical sidewall  137  which extends from the flange opening  149  in outer wall  141 , past end portion  151  of inner wall  139 , and into chamber  25 . The sidewall  137  of neck  117  terminates within chamber  25  at a medial location, preferably one proximate to the volumetric center of the volume defined by inner wall  139 . 
   Sidewall  137  of neck  117  define a cross-sectional area which is sized to receive therein, either wholly or partially, several of the operative components described previously, including the alignment piece  119 , probes  51 ,  65 , and fill tube  71 . The arrangement of these components nonetheless does not completely occupy the cross-sectional area of neck  117 , leaving open at least one, longitudinal passage  75 . 
   Passage  75  delivers gaseous oxygen from volume  31  to delivery system  35 . Passage  75  has an opening located in the middle of chamber  25  by virtue of neck  117  terminating at such middle location. This configuration makes it very difficult for oxygen in the liquid phase to inadvertently exit through passage  75  during use of liquid oxygen system  25 , no matter how the user may turn it during use thereof. This is especially important when system  21  is portable, as in the preferred embodiment of this invention, since such portable systems may be turned, jostled, or may be otherwise not resting on their bases while in use. By way of example, if liquid system  21  were turned on its head, volume  29  of liquid oxygen would move from base  89  and collect at the opposite end of chamber  25  along end portion  151  of inner wall  139 . During such movement, the slight amount of liquid oxygen which may enter neck  117 /passage  75  is generally insufficient to escape system  21  in liquid phase, generally boiling off harmlessly; furthermore, once system  21  is turned on its head, the extension of neck  117  into chamber  25  exceeds the level of the liquid oxygen received therein, due to the partial filling of chamber  25 . As such, no further liquid oxygen escapes out neck  117 . The same principles apply to any orientation of system  21  during its use to prevent inadvertent release of liquid oxygen. 
   The above features of system  21  improve the efficiency at which liquid oxygen is used by avoiding excess “boil off” or entrainment of liquid oxygen when the system is inverted or turned. In other words, the liquid oxygen in system  21  is depleted at rates substantially independent of the orientation of container  23 , since no inadvertent or excess use of liquid oxygen occurs when the system is inverted or turned during use. 
   The upper end of passage  75  serves as the inlet for gaseous oxygen to enter delivery system  35 . The upper end of passage  75  connects to manifold chamber  115 . Manifold chamber  115  is in communication with flow rate controller  37  by means of passage  155  ( FIG. 1 ). Flow rate controller  37  includes a user-rotatable dial or selector  38 . Selector  38  is rotatably mounted to manifold  113  at a suitable angular location thereon so that it is accessible by the user to turn it to select the desired flow rate ( FIGS. 3 ,  4 ). 
   Flow rate controller  37  is in communication with conserver  43 . Preferably, conserver  43  comprises part of head  93 , is located adjacent to manifold  113  along longitudinal axis  85 , and is secured to opposing upper surface  94  of manifold  113 . Conserver  43  includes a reservoir manifold  157  with a passage  159  defined therein communicating between the selected orifice  39  of flow rate controller  37  and reservoir  41  of conserver  43 . Thus, gas flows from manifold chamber  115 , through passage  155  ( FIGS. 1 and 4 ) to orifice  39 , through passage  159  in reservoir manifold  157 , and into reservoir  41 . The flow is such that reservoir  41  gets charged with a volume of gaseous oxygen at a corresponding pressure, such volume determined by the size of orifice  39  selected by the user. 
   The general operating principles of one suitable pneumatic-type conserver are described in co-pending application Ser. No. 10/040,190, of common assignee, the teachings of which are incorporated herein by reference. 
   The gas in manifold chamber  115  charges conserver chamber  161  ( FIG. 2 ) through suitable passage  163  ( FIG. 1 ). Sensing diaphragm  49  is mounted at the upper edge of reservoir manifold  157  ( FIG. 2 ) and comprises part of sensing system  45  ( FIG. 1 ). As such, sensing diaphragm  49  is normally seated against an orifice  165 . Orifice  165 , in turn, communicates with conserver chamber  161 . Chamber  161  is also in communication with dump diaphragm  50 , which is shown mounted below conserver chamber  161  and sensing diaphragm  49  in the drawings ( FIG. 2 ). It will be appreciated that in conservers of the pneumatic type, dump diaphragm  50  is seated against a corresponding orifice  167  by virtue of the pressure maintained in conserver chamber  161 . Sensing diaphragm  49 , in turn, is generally seated by a suitable mechanical force urging it toward orifice  165 , such as an adjustment screw spring. Passage  169  ( FIG. 1 ) is suitably defined within head  93  so that the outer side of sense diaphragm  49 , that is, the side opposite conserver chamber  161 , is in communication with gas line  47  connected to the user. Similarly, delivery passage  171  ( FIGS. 1 ,  2 ,  4 ) has been defined at suitable locations within head  93 , including through reservoir manifold  157  and manifold  113 , to connect reservoir  41  to gas outlet  173 , whereby the gas from reservoir  41  is delivered out outlet  173 , through gas line  47  to the user. Outlet  173  has been configured to form nozzle  179  for attaching to a correspondingly-shaped end of gas line  47 . Conserver  43  is configured so that delivery passage  171  is opened or closed by the corresponding opening or closing of orifice  167  by dump diaphragm  50 . Vent to atmosphere  175  ( FIG. 1 ) is defined by suitable portions of head  93  to lead from the side of sensing diaphragm  49  which seals against orifice  165  out to the ambient. 
   Although conserver  43  has been described with reference to one type of pneumatic device, any number of alternate pneumatic configurations would be suitable to enable delivery system  35  to operate, and even non-pneumatic conservers  43  are suitable. 
   Having described the various structures and features of the cryogenic, gas delivery system  21 , its operation is readily apparent to those skilled in the art. A volume  29  of liquid oxygen needs to be introduced into chamber  25 , and a volume  31  of pressurized oxygen needs to be generated within chamber  25 . Gas volume  31  needs to be charged or pressurized up to the predetermined baseline pressure for the system  21 . In this embodiment, to achieve a baseline pressure of about 50 psi, regulator  33  is preferably configured so that first portion  53  of variable probe  51  abuts against opposing surface  67  of probe  65  during the initial stages of filling system  21  with liquid oxygen from base unit  22  ( FIG. 4 ). In this fully biased position, regulator  33  introduces the maximum amount of thermal energy into system  21  to “charge” it up to the required baseline pressure. As the system fills, and the volume  31  of pressurized oxygen approaches the desired baseline pressure, such pressure urges probe  51  away from probe  65 , thereby reducing the amount of thermal energy introduced into chamber  25 . Eventually, regulator  33  reaches an equilibrium and maintains the pressure of volume or headspace  31  within the predetermined range of baseline pressures and corresponding evaporation rates, as discussed previously, during operation of system  21 . 
   System  21  is preferably charged by being connected to a base unit  22 , such as that shown in  FIG. 4 . Prior to filling, vent-to-fill valve  73  is actuated by the user&#39;s rotating the handle  135  so that its cam opens valve  73 . During filling, gaseous oxygen escapes through vent-to-fill valve  73 , permitting the volume  29  of liquid oxygen to enter chamber  25 . Filling of chamber  25  with liquid oxygen continues with system  21  on its side in this embodiment, with liquid oxygen eventually encountering the trapping mechanism  127 , and eventually reaching a level corresponding to upper edge  133  of wings  129 . Further filling of the device  129  is impeded at this point as liquid oxygen begins to flow back out neck  117  into head  93 , where it boils off or exits the system. Vent-to-fill valve  73  is then closed and system  21  disconnected from base unit  22 . 
   The fact that oxygen delivery passage  75  opens into chamber  25  near its volumetric center permits system  21  to be held in any orientation during filling and yet still only be partly filled with liquid oxygen when the filling is complete. Thus, for example, if, in an alternative embodiment, the connection between base unit  22  and system  21  were to orient the system  21  in an upright position, the pressure of the gas volume  31  acting on the liquid oxygen volume  29  would generally cause liquid oxygen to flow back out passage  75  once the chamber becomes about 50% full. Similarly, if system  21  were being filled in a completely inverted position, liquid oxygen would fill to the level corresponding to the opening of passage  75 , about 50% of the volume of chamber  25 , and thereafter would begin to flow out of passage  75 . 
   Once system  21  has been charged with the appropriate volume of liquid oxygen, the back flow or out flow of excess liquid oxygen exits vent  73  with enough steam and entrained liquid oxygen so as to be discernible to the user. The venting of excess liquid oxygen thus signals to the user that the system is fully “loaded” or “charged” for subsequent use. 
   After the system  21  has been charged and disconnected from its filling source, it is available for both sedentary and ambulatory applications. The gas to be delivered to the user enters delivery system  35  from chamber  25  in gaseous—not liquid—phase. Gaseous oxygen exits container  23  from gas volume  31  through passage  75 , and flows through the user-selected orifice  39  of flow rate controller  37 . The orifice selection controls the saturation or delivery rate of oxygen to the user. The delivery system  35  is calibrated so that orifices  39  correspond to the delivery to the user of different saturation levels or volumes of oxygen per minute. Flow-rate controller  37  thus allows the user to set the system to achieve the saturation or liters per minute of oxygen prescribed by medical circumstances, or as required to suit particular activities of the user. 
   During use of system  21 , a variety of factors may cause the pressure of volume  31  to vary; however, regulator  33  responds to such variations by moving probe  51  toward or away from chamber  25 , as required. Thus, for example, a user may place increased oxygen demands on the system, either by breathing more frequently or selecting a larger delivery volume by appropriate turning of flow rate selector  38 . If such actions create a drop in pressure, it is only momentary, because regulator  33  operates to increase the transfer of thermal energy into the system by moving probe  51  toward chamber  25 . More gaseous oxygen boils off as a result, returning the pressure of chamber  25  to the baseline pressure range. The converse occurs if the system is not used, or if oxygen demand decreases. 
   If the system  21  is charged but not used for a certain amount of time, the “use-it-or-lose-it” nature of liquid oxygen is such that it continues to evaporate at the rate which characterizes system  21 . Accordingly, container  23  is equipped with suitable relief valves to maintain the appropriate baseline pressure in volume  31  when no oxygen is being drawn out of chamber  25  by delivery system  35 . A primary relief valve (not shown) is provided to avoid over-pressurized conditions. Additionally, when vent-to-fill valve  73  is closed, it serves as a secondary relief valve. When the pressure in head  93  exceeds a predetermined, secondary threshold, the pressure acts against the force of spring  100  to urge seal  103  away from its seat  105  and opens valve  73  to atmosphere. 
   Inhalation by the user creates a negative pressure in distal end  77  of gas line  47  connected to the user. The negative pressure travels through gas line  47 . The other end of gas line  47  is in communication with sensing system  45 , so the negative pressure is transmitted to sensing system  45 , where it acts upon sense diaphragm  49 . There, the negative pressure unseats diaphragm  49  from orifice  165  against which it is biased and, by opening such orifice, a flow path is established which vents pressurized oxygen from the other side of diaphragm  49  through vent to atmosphere  175 . The venting of pressurized oxygen to atmosphere, in turn, reduces pressure in conserving chamber  161  sufficiently so that dump diaphragm  50 , which is normally biased against orifice  167  to close reservoir  41 , opens in response to the reduced pressure. The opening of reservoir  41  creates a flow path from reservoir  41  to gas line  47 , thereby delivering gas from reservoir  41  as a pulse to the user in response to inhalation. 
   Passage  163  to conserver chamber  161  includes a restriction  177  ( FIG. 1 ). Restriction  177 , orifices  165 ,  167 , and other flow characteristics of conserver  43 , are all selected or tuned so that gas pressure is returned to appropriate locations in conserver  43  at suitable times and pressures. As such, the appropriate amount of oxygen is delivered to the user before the pressures reseat dump diaphragm  50  to end oxygen delivery to the user. 
   The above-described process for delivering oxygen to the user is repeated in response to the inhalation pattern of the user. Oxygen is thus continually drawn off of gas volume  31  over time, and the gas volume  31  is replenished by evaporation of the liquid oxygen in chamber  25 . The evaporation rate of such liquid oxygen is regulated by regulator  33 , as discussed previously, to assure that volume  31  remains sufficiently charged during the operation cycle by the user. The system continues to supply needed oxygen until the volume of liquid oxygen  29  is depleted. At this point, the system is refilled with liquid oxygen by any suitable means, including in the manner discussed previously, and the user again is free to operate the system through a range of activities. 
   Liquid oxygen system  21  can be sized and configured in any number of ways, so long as the system evaporates sufficient liquid oxygen, which, in turn, is drawn off by delivery system  35  in volumes sufficient to supply the user&#39;s needs through the range of such user&#39;s activities. In one preferred embodiment, the chamber  25  and regulator  33  are configured so that the system  21  has an evaporation rate capable of ranging from 0.4 liters to 1.5 liters per minute. Conserver  43  is configured to cause a four-fold increase in the effective volume of oxygen delivered to the user. Flow rate controller  37  includes orifices  39  corresponding to effective delivery volumes ranging between one and four liters per minute. 
   Regulator  33  preferably has variable probe  51  with its elongated portion or shaft made out of copper and, optionally, its head portion  56  made of metallic material, preferably copper as well. Probe  65  is preferably made of a metal with high heat conductivity, more preferably copper. 
   In contrast, to reduce transfer of thermal energy, fill system  27  preferably makes use of stainless steel, such as in chuck  69  and fill tube  71 . The baseline pressure is preferably about 50 psi, plus or minus about 2 psi, making the lower pressure threshold about 48 psi, the upper pressure threshold about 52 psi, and the range between the thresholds about 4 psi. Under normal operations, the gap between the opposing tips of probes  51 ,  65 , is about one quarter inch. 
   The volume of chamber  25  is preferably about 39 cubic inches, resulting in volume  29  of liquid oxygen being about 19 cubic inches, and volume  31  of gaseous oxygen being about 20 cubic inches when the system has been fully charged with oxygen. 
   The various passages and orifices in conserver  43  are sized so that conserver  43  acts, in a sense, like a “clock,” determining how long for reservoir  41  to charge to its desired pressure and how long to leave dump diaphragm  50  open for delivery of oxygen through gas delivery line  47 . Although many different combinations of orifices and passage sizes can achieve the desired “clocking” function of conserver  43 , one suitable set of dimensions is as follows: 0.0015 to 0.0020 inches for restriction  177  in pressure line passage  163 , 0.008–0.014 inches for orifice  165  for sensing diaphragm  49 , and 0.040 to 0.100 inches for orifice  167  for dump diaphragm  50 . 
   Although the invention has been described with reference to certain preferred embodiments, alternative embodiments are likewise within the scope of the present invention. For example, system  21  can be designed without requiring fixed probe  65 , so long as variable probe  51  introduces sufficient thermal energy to charge delivery system  35  with the required amount of gaseous oxygen. Still further, regulator  33  can be replaced entirely with a system of structures extending from the ambient into the container, that is, there is no need for a movable probe  51  or a probe  65 . In this alternative, the structures entering chamber  25  would be sufficient to charge delivery system  35  for all intended uses. 
   In still another alternative, the system could include means for the user to set the distance between probes  51  and  65 , the varying of the distance resulting in a corresponding variation in the evaporating rate of oxygen and a corresponding variation in the volume of oxygen delivered to the user through the delivery system  35 . 
   Excess evaporation could be vented to atmosphere under these alternative scenarios. 
   In further alternatives, the physical location of conserver  43  can be varied from its preferred position longitudinally adjacent to head  93 . 
   In still further embodiments, conserver  43  need not be secured to system  21 , that is, it need not be secured to either container  23  or head  93 . Instead, conserver  43  can either be dispensed with entirely or incorporated remotely from the portable system  21 . Conserver  43  is alternately any other type of pneumatic conserver, including one without a reservoir, or any non-pneumatic type. 
   As still further alternatives, flow rate controller  37 , vent-to-fill valve  73 , fill chuck  69 , and nozzle  179  need not all be secured at respective angular locations in head  93 , but can instead by interconnected at different locations relative to container  23 , so long as the various systems remain operatively connected to each other to effectuate the operation of system  21  as intended. 
   The ratio of gas volume  31  and gas volume  29  need not be 1 to 1, that is, the partial filling of system need not be only at 50%. Rather, suitable traps or other structures can be implemented to permit increased amounts of liquid oxygen, or less liquid oxygen can be used in the system. 
   The advantages of the invention are apparent from the foregoing description. 
   As one advantage, gas is delivered by a delivery system without using high pressure gas cylinders. 
   Another advantage is that a liquid oxygen system is provided which does not need warming coils to deliver oxygen in gas form. 
   As still a further advantage, the invention makes use of a fill system which is structured and located to charge the system with liquid oxygen more efficiently by reducing the amount of thermal energy to which the liquid oxygen is exposed during the filling operation. 
   As yet another advantage, the invention reduces the inadvertent escape of liquid oxygen from the system because it is structured to fill only partially, and locates the various fill and delivery components at medial locations within chamber  21 . This allows liquid oxygen in the system to be used more efficiently. 
   Having described the invention with certain preferred and alternative embodiments, it is understood that still further alternatives and variations are possible, as skill or fancy may suggest, and such variations are likewise within the scope of the present invention, which is only limited by the following claims, and is not limited by the preferred embodiments described herein.