Gas delivery system

Abstract: A gas delivery system includes a capsule 4 for storing a propellant fluid, eg. helium under pressure. The capsule 4 is provided with a stopper 5 having a stem 16 formed with a frangible section 18. In use, mechanical means 9 is employed to rupture the stem 16 about the frangible section 18 to release the helium under high pressure between 60 and 80 bar.

Description: The present invention relates to gas delivery systems and in particular to capsules for containing small volumes of fluid at high pressure, that-is, between 60 and 80 bar for use in such systems. Sealed capsules are well known in circumstances where the force of the fluid under pressure is employed to dispense a substance such as discharging draught beer from a beer dispenser or expelling soda water from a soda siphon. It is also known to employ sealed capsules containing helium at high pressures in the order of 30 - 40 bar in medical devices using the energy of the pressurised helium to drive a therapeutic agent through the skin of a patient. In PCT published application WO94/24263 there is described a needle-less syringe, which includes a metal capsule containing helium gas at high pressure which is used to force particles of a therapeutic agent through the skin of a patient in a substantially painless manner. The capsule is detachable from the remainder of the syringe and once used, either a new charge of gas can be placed in the capsule or more favourably the capsule can be discarded and a new capsule charged with gas can be attached to the remainder of the syringe. In the circumstance where the gas capsule is a throw away item it is important that it can be manufactured simply and cheaply. In medical applications helium gas is a favoured fluid since it is very light which makes it suitable for use as a propellant for therapeutic agents in that when it impinges against the skin of a patient it will bounce off into the atmosphere and not pass through the skin of the patient However, helium because it is light, is difficult to contain since it will leak through the most minuscule fault in a container. Furthermore, in medical applications it is important that the helium gas can be released from the gas capsule with the minimum of force by the user, for example, finger force. UK Patent 253744 describes a gas delivery system including a metal capsule for gases or liquids under pressure which can be used to inflate a flexible container. The capsule includes a hollow body with a neck extending therefrom and a stopper located in the neck in a fluid type manner. The stopper has a stem extending outwardly from the neck which the stem is form with a passage in communication with the interior of the hollow body. The stem has an external thread for connection to a handle forming part of the flexible container, so that when it is required to liberate the gases or liquids in the capsule the hollow body is moved laterally relative to the handle and the stem connected thereto such that the stem is ruptured thereby releasing the gas or fluid from the interior of the hollow body. The capsule described is not effective for containing a very light gas such as helium for a reasonable length of time at pressures in the order of 60 to 80 bar since the helium molecules will leak through the helical path between the co-operating internal thread of the neck portion and external thread on the closure member. Furthermore, in order to break the stem a considerable laterally force needs to be applied, that is, a force greater than finger pressure having no mechanical advantage. A further disadvantage is that the capsule is expensive to manufacture in that screw threads have to be turned on both the neck portion and the closure member. It is an aim of the invention to provide in a gas delivery system a capsule for fluid under high pressure which can be manufactured simply and cheaply. It is a further aim to provide a capsule for fluid under pressure for example, helium gas, which is substantially leak-proof. It is yet a further aim to provide a capsule which can be opened with a finger pressure having no or relatively very little mechanical advantage without causing the gas delivery device of which it forms a part, to move when held in one hand. According to the invention, a gas delivery system comprises a capsule for storing fluid under pressure having a hollow body with a neck extending therefrom, a stopper located in the neck in a fluid tight manner, the stopper having a stem including a frangible section, the stem extending outwardly from the neck and formed with a passage in communication with the interior of the hollow body and mechanical means for rupturing the stem about the frangible section thereby allowing the escape of fluid through the passage from the hollow body in which the stopper is laser welded within the hollow neck . In one embodiment of the invention the stem may be formed at a right angle with a major portion of the stem above the frangible portion at substantially right angles to the hollow neck. Embodiments of the invention will now be described, by way of example, reference being made to the Figures of the accompanying diagrammatic drawings in which:- Figure 1 is a diagrammatic sketch of a needle-less medical device including a gas delivery system of the present invention; Figure 2 is a side view of a hollow neck of a first capsule for storing a fluid under pressure; Figure 3 is a view similar to Figure 2 of a second embodiment of capsule for containing a fluid under pressure. Figure 4 is a view similar to Figures 2 and 3 of yet a further embodiment of a gas capsule for containing a fluid under pressure; Figure 5 is yet a further view similar to Figures 2, 3 and 4 of yet a further embodiment of a capsule for containing a fluid under pressure, and Figure 6 is a diagrammatic sketch similar to Figure 1 but showing a different mechanical means for rupturing a gas capsule. As shown in Figure 1, a needle-less medical device is in the form of a needle-less syringe 1 which comprises essentially a casing 2 in the form of an elongate hollow tube open at a distal end to define an outlet 3. The casing 2 contains a gas capsule 4 for storing a fluid, for example, helium under high pressure, that is between 60 and 80 bar. An inclined surface 9 is formed on the interior of the surface of the casing 2 spaced from but adjacent to a stopper 5 of the gas capsule 4. The gas capsule 4 is so mounted within the casing 2 that when a finger pressure is applied to the proximal end of the gas capsule 4 the capsule will move downwardly (as shown) until the stopper 5 strikes the surface 9. Within the casing 2 adjacent the stopper 5 of the gas capsule 4 there is formed a chamber 6 for receiving a powdered agent, for example, a drug 7. Referring also to Figure 2, the gas capsule 4 comprises a hollow body 10 with a hollow neck 12 extending therefrom. The stopper 5 is located within the neck 12 in a fluid tight manner. In this embodiment the stopper 5 is laser welded within the hollow neck 12. The stopper 5 includes a stem 16 extending outwardly from the hollow neck and including a frangible section 18. The stopper 5 also has formed therein a passage 20 which communicates at one end with the interior of the hollow body 10 and extends past the frangible section 18 to terminate in a blind hole. In use, when it is desired to treat a patient by means of the syringe 1, the drug 7 is placed in the chamber 6 and the outlet 3 is placed against the skin of the patient. Finger pressure is applied to the proximal (upper as shown) end of the gas capsule 4 which causes the capsule 4 to move downwardly until the stem 16 engages the inclined surface 9 thereby rupturing about the frangible section 18 with the subsequent release of helium. The released helium passes out from the capsule 4 into the chamber 6 where it entrains the powdered drug 7. The helium with the entrained powdered drug 7 then passes through the outlet 3 with the drug passing through the skin of the patient whilst the light molecules of helium bounce off the skin into the atmosphere. In the embodiment of gas capsule 4 illustrated in Figure 3, the structure is substantially the same as with the capsule 4 illustrated in Figure 2 with the exception that the free end 14 of the hollow neck 12 is crimped about a shoulder of the stopper 5 to maintain the stopper in a gas tight manner within the hollow neck 12. Referring now to Figure 4, again the stopper 5 is substantially as described with reference to Figures 2 and 3, however the stem 16 is configured such that a major part beyond the frangible section 18 is at right angles to the remainder of the stem. This configuration is of particular utility when, instead of a inclined surface 9, as illustrated in Figure 1, a simple abutment is used to exert a force adjacent the free end of the stem 6 to rupture the frangible section 18. The embodiment illustrated in Figure 5 is very similar to that illustrated in Figure 4 except that the stem 16 terminates in two parts each at right angles to the remainder of the stem with the frangible section 18 immediately above the blind end of the passage 20. Referring now to Figure 6, this illustrates the upper portion of a needle-less syringe similar to that illustrated in Figure 1 but in which the stem 16 of the stopper 5 is caused to rupture about the frangible section 18 by means of a mechanical push button lever device. The lever device includes an arm 30 mounted for pivotal movement about a pivot point 32. One end of arm 30 is formed with a cup-shaped member 34 which embraces the free end of the stem 16. The portion of the arm 30 below (as shown) the pivot point 32 is formed through 90° and terminates in a push-button 36 located outside the casing 2 of the needle-less syringe. In use, finger pressure on the push-button 36 will cause the cup-shaped member 34 to pivot in a clockwise sense about the pivot point 32 and thereby rupture the stem 16 about the frangible section 18. This embodiment ensures that when the stem 16 is ruptured about the frangible section 18, the free end of the stem which separates from the remainder of the stem cannot be propelled towards the patient but is held captive by the cup-shaped member 34. The capsules 4 may be made from aluminium or an aluminium alloy and, if necessary may be reinforced with an outer layer of a different material which could be in the form of a lattice wound tightly around a substantial part of the hollow body 10. Furthermore, the hollow body 10 on its interior surface, which may not be impervious to helium, can be provided with a layer of flexible material such as aluminium foil over a major portion of its surface which is impervious to helium and effectively blocks the flow of gas from the hollow body 10 into the passage 20 in the stopper 5. With this modification, after the frangible section 18 is ruptured, a spike extends through the passage 20 to rupture the flexible material in order to enable the helium under pressure to exit from the hollow body 10. It will be appreciated that all the capsules described with reference to the above embodiments are relatively inexpensive to manufacture and furthermore are relatively leak proof but easy to open. Although reference has been made to use of the capsules 4 with a needle-less syringe for medical purposes, there are a number of other applications where the force of the contained fluid can be utilised. For example, in the inflation of balloons bearing fluorescent markings for identification by radar and for the inflation of life jackets dinghies. The energy of the pressurised fluid could also be utilised in a weapon to act as a propellant for a bullet or other projectile.

Claims: A gas delivery system comprising a capsule (4) for storing fluid under pressure having a hollow body (10) with a neck (12) extending therefrom, a stopper (5) located in the neck (12) in a fluid tight manner, the stopper (5) having a stem (16) including a frangible section (18), the stem (16) extending outwardly from the neck (12) and formed with a passage (20) in communication with the interior of the hollow body (10) and mechanical means for rupturing the stem (16) about the frangible section (18) thereby allowing the escape of fluid through the passage (20) from the hollow body (10) characterised in that the stopper (5) is laser welded within the hollow neck (12). A gas delivery system as claimed in Claim 1, in which the stopper is maintained within the neck by crimping the free end of the neck over a shoulder formed on the stopper. A gas delivery system as claimed in Claim 1 or Claim 2, in which the mechanical means includes surface for engaging and thereby exerting a lateral force on the stem for rupturing the frangible section. A gas delivery system as claimed in Claim 1 or Claim 2, in which the mechanical means includes an arm mounted for pivotal movement, one end of which arm is formed with a cup-shaped member which embraces the free end of the stem and the other end of which arm terminates in a push-button, the arrangement being such that a force on the push-button will cause the arm to pivot thereby rupturing the stem about the frangible section. A gas delivery system as claimed in Claim 1 or Claim 2, in which a major part of the stem beyond the frangible section is orientated at right angles to the remainder of the stem. A gas delivery system as claimed in Claim 5, in which the mechanical means includes at least one abutment for engaging and thereby exerting a force at or adjacent the free end of the stem for rupturing the frangible section. A gas delivery system as claimed in any one of Claims 1 to 6, in which the fluid is helium and is stored in the capsule at a pressure between 60 and 80 bar. A gas delivery system as claimed in any one of Claims 1 to 7, in which at least a portion of the inner surface of the hollow body is covered with a flexible material impervious to the helium. A gas delivery system as claimed in any one of Claims 1 to 8, in which the capsule is provided with a reinforcing material around its outside surface. A capsule for storing fluid under pressure for use with a gas delivery system as claimed in any one of Claims 1 to 9.

Inventors: BIRCH DAVID W, SHERVINGTON EVELYN A, BIRCH, DAVID W., SHERVINGTON, EVELYN A.
Applicants: BOC GROUP PLC, THE BOC GROUP PLC
Application year: 1996
Main classification: F17C7
IPC codes: A61M5, F17C13, A61M11, F17C7, B65D47, A61J1