GB2215830A

GB2215830A - Apparatus for supplying a vapour free of liquid from a pressurised container

Info

Publication number: GB2215830A
Application number: GB8805509A
Authority: GB
Inventors: John Walter Rilett
Original assignee: Metal Box PLC
Current assignee: Crown Packaging UK Ltd
Priority date: 1988-03-08
Filing date: 1988-03-08
Publication date: 1989-09-27
Also published as: GB8904697D0; GB2219843A; GB8805509D0; GB2219843B

Abstract

Apparatus attachable to a pressurised container of a pressure-liquefiable gas, for supplying vapour substantially free of liquid irrespective of the attitude of the apparatus and container, comprises a chamber (24) with an entry passageway (30) incorporating a non-return valve (29) and an exit conduit (31) extending from an opening (311) in the vicinity of the centre of volume of the chamber (24). The apparatus may also incorporate a pressure-regulating mechanism (35) in the form of a poppet valve (36) controlling the vapour outlet (42) and urged by a spring (37) against a valve seat (38), and a control piston (39) urged by a further spring (40) against the poppet to open the valve, the pressure of further spring (40) being controlled via a plunger (41) and hand-squeeze lever (43). <IMAGE>

Description

APPARATUS FOR SUPPLYING A VAPOUR FREE OF LIOUID FROM A PRESSURISED CONTAINER The present invention relates to apparatus for supplying a vapour substantially free of liquid from a pressurised container of a pressure-liquefiable gas containing a mixture of said vapour and liquid and which, when attached to such a container, will allow vapour to be supplied whether the container is upright, inverted or in any other attitude.

In addition, the present invention may provide means to control the pressure of the vapour supplied by the apparatus.

Pressurised containers of pressure-liquefiable gases such as carbon dioxide and fluorinated hydrocarbons normally contain liquid phase to a certain depth together with vapour phase in the ullage space above. If the container remains substantially upright and its outlet valve is (as is normal) at the top of the container, vapour phase can be withdrawn through the said outlet valve. Such withdrawal of vapour phase (rather than liquid phase) is desirable in a number of practical applications of such containers, for example devices which use pressurised carbon dioxide as a source of mechanical power, portable "carbon dioxide" welding equipment and certain aerosol dispensers.

However, if such a container is inverted, held horizontal or otherwise moved to an attitude substantially away from the upright posture, it is no longer possible to withdraw the desired vapour phase because the container's outlet valve becomes flooded with liquid phase, causing liquid rather than vapour to be withdrawn from the container; such withdrawal of liquid phase may then cause a malfunction such as excessive pressure arising from volatilisation of liquid, or formation of solid phase, in the device being supplied by the container.

To review the background art, the historical practice is to employ containers of pressure-liquefiable gases (called "cylinders") in an upright attitude (so that the outlet valve is at the top), whereby opening of the outlet valve allows vapour phase to be supplied. Sometimes, such containers are fitted with "dip tubes" (a length of rigid tubing which leads from the base of the cylinder to its outlet valve) which cause liquid phase to be supplied when the cylinder is upright or, alternatively, allow the cylinder to be employed in an inverted attitude while supplying vapour phase.

Cylinders which are charged with carbon dioxide (sometimes with admixture of nitrogen) and employed for the inflation of life-rafts are conventionally held close to a horizontal attitude during discharge into the life-raft; as such usage normally requires liquid phase to be discharged, the normal practice is to employ a flexible dip tube (called a "siphon tube") with a weighted tip which falls to the lowest level of the cylinder's interior and which thus is suitably submerged below the liquid level during discharge into the life-raft.

A technique which is sometimes used to supply vapour phase from a cylinder of carbon dioxide involves the use of an electrical heater; liquid carbon dioxide (or a mixture of its liquid and vapour phases) is supplied to a device which incorporates an electrical resistance heater with the object of supplying the heat energy necessary to vaporise any liquid phase. However, this device is necessarily dependent on a supply of electrical energy.

In UK Patent No. 1595332, means are described for the supply of vaporised carbon dioxide which involve the use of a "power capsule" provided with both a "buffer substance" and a gas offtake positioned in the vicinity of the centre of volume of a vessel charged with carbon dioxide, as means of supplying carbon dioxide vapour to a motor. However, such a device is dependent on being charged with carbon dioxide and is not adapted for use with a carbon dioxide container.

According to the present invention, in its simplest form, there is provided apparatus for supplying a vapour substantially free of liquid from a pressurised container of a pressure-liquefiable gas containing a mixture of said vapour and liquid, said apparatus comprising a chamber, means for attaching the chamber to the container, an entry passageway incorporating a non-return valve for introducing said mixture into the chamber, and an exit conduit extending from an opening in the vicinity of the centre of volume of the chamber, so that substantially only vapour will leave through the exit conduit, irrespective of the attitude of the chamber, until the level of the liquid has risen to reach the vicinity of the centre of volume of the chamber.

The benefit of the present invention (which is not achieved by prior known art) is that it provides apparatus which, when attached to a container of pressureliquefiable gas, converts that container which might otherwise supply only liquid phase into a combination which, for a useful and suitable working period, supplies only vapour phase. This vapour phase may then be used to supply a device which requires vapour phase to operate correctly or which might malfunction if supplied with liquid phase.

In operation, liquid phase from the said container flows into the chamber of the present invention via the said inlet and the said non-return valve and, as it does so, a proportion of it volatilises into vapour whilst drawing its latent heat of vaporisation from the materials of construction of the said chamber, which should preferably be of a metal of relatively high thermal conductivity to encourage heat flow. It is found that, for a suitable working period, the residual liquid phase in the said chamber occupies less than half the contained volume of the chamber and, accordingly, has a liquid level which falls short of the "half full" condition; that is to say, the liquid level will be lower than the point which is called the "centre of volume" of the chamber; this will be true whatever the attitude of the chamber and of the container to which it is attached.Therefore, the opening provided by the present invention and positioned in the vicinity of the centre of volume of the chamber will not become flooded by liquid phase and, accordingly, only vapour phase will enter the said opening.

It is found that, during extended operation, the described heat flow from the materials of the chamber causes them to become chilled and this in turn causes condensation of some of the vapour and hence a gradual increase in the liquid level within the chamber; eventually, the liquid level may rise far enough to flood the said opening, causing some liquid phase to be supplied by the apparatus. This undesirable effect can be delayed (so as to allow a longer working period) by increasing the size of the chamber. In an embodiment of the present invention adapted for use in a CO2- powered tree pruner it is found the said chamber may suitably have a volume (for the containment of fluid) typically in the region of 10% of the capacity of the container to which it is to be attached but, in other embodiments the chamber may have a greater volume if it is to operate for longer working periods.

Working periods may of course be repeated if a "rest period" is allowed between successive working periods, such rest period being long enough to allow the chamber to recover heat energy by natural heat flow from the surroundings. Alternatively, a heat storage substance (sometimes called a "buffer" substance) may be provided in thermal communication with the chamber and/or its contents, so as to supply the needed heat energy from a change in phase of the buffer substance, using known prior art. A further alternative is to supply the needed heat energy from a source of artificial heat (for example an electrical resistance heater, an adsorbent or persorbent material, or a heat exchanger fed for instance with a warming liquid) although this of course detracts from the basic simplicity of the present invention in its described simplest form.

The non-return valve mounted in the entry passageway of the chamber performs three useful functions. Firstly, it allows flow of fluid in a forward direction from the said container and into the said chamber; secondly it prevents backward escape of fluid from the chamber (if it is detached from the said container) which might otherwise be both alarming and dangerous; and thirdly it allows the chamber when charged with fluid to provide a source of vapour for a limited but useful period even when detached from the said container.

The apparatus of the present invention may, if desired, include a pressure regulating mechanism to control the pressure of the vapour supplied by it. The pressure regulating mechanism is supplied with vapour at the internal pressure existing in the chamber and, for this purpose, the exit conduit leading from the opening in the vicinity of the centre of volume of the chamber communicates with the said pressure regulator. One embodiment of the present invention has means to control the output pressure of the said pressure regulator in an easy manually-operated manner.For example in a tree-pruner (as described later herein), a hand-squeeze lever is adapted to control the output pressure of the pressure regulator so that a progressive increase in the squeezing force applied to the said lever causes a progressive and corresponding increase in the pressure-regulator's output pressure which drives the tree pruner. By this means only the needed driving pressure is supplied to the tree pruner (whatever the size of the branch being pruned or lopped) and a substantial economisation in gas usage is achieved.

An embodiment of the present invention will now be more particularly described, by way of example, and with reference to the accompanying drawings, in which: Figure 1 shows, in perspective, a form of vapour offtake regulator according to the present invention attached to a pressurised container supplying carbon dioxide to power a tree pruner, and Figure 2 show, in longitudinal section, the form of vapour offtake regulator illustrated in Figure 1.

Referring to Figure 1, this shows a tree-pruner 1 powered by carbon dioxide from a pressurised container 2, e.g. of approximately 325cc capacity. Attached to the container 2 is a vapour offtake regulator 3 incorporating a pressure regulator 4 which is controlled by manual squeezing of the hand lever 5. The capacity of the vapour offtake regulator may be approximately 32cc, i.e. 10% of the capacity of the container 2.

The CO2 vapour produced by the vapour offtake regulator 3 is led through an outlet 6 to a hollow shaft 7 (shown foreshortened in Figure 1) and then to a pruning head 8 which incorporates an internal power cylinder, a pruning blade 9 acting against an anvil 10, and a return spring 11.

In operation, the vapour offtake regulator 3 accepts CO2 (being vapour if the container 2 is at or near a vertical attitude, and liquid if the container is inverted or in an attitude substantially away from the vertical) and, by virtue of its construction according to the present invention, supplies only vapour to the pressure regulator 4, the outlet 6, hollow shaft 7 and pruning head 8, for a suitable working period. The pruning blade 9 and anvil 10 are placed into position so as to embrace the tree-branch to be pruned, whereupon the hand lever 5 is squeezed with a progressively-increasing force. This causes a progressive increase in the pressure of the vapour supplied by the pressure regulator 4, and a corresponding progressive increase in the cutting force applied by the pruning blade 9 on the tree-branch, until the tree-branch is severed.Thereupon, the hand lever 5 is released, allowing the pruning blade 9 to open away from the anvil 10 under the action of the return spring 11. The process can then be repeated on another tree-branch.

Thus, during the above-described process, the present invention causes only the necessary pressure of CO2 vapour to be supplied to the pruning head 8, rather than the full internal pressure of the container 2, and thus allows a substantial economy in usage of CO2.

Referring to Figure 2, this shows in longitudinal cross-section the vapour offtake regulator that is identified by reference numeral 3 in Figure 1. A passage-defining member in the form of a tie-bar 20, advantageously made from an aluminium alloy diecasting, is screw-threadedly engaged by means of screw threads 21 to a body member 22. A tubular shell 23 of high tensile aluminium alloy bridges between the tie-bar 20 and the body member 22, being sealed to each of those parts by the '0' Ring seals 25 and 26 so as to create an internal chamber 24 having a volume of, for example, approximately 32cc.

The tie-bar 20 is provided with female screw-threads 27 for engagement with the male screw-threaded outlet of the conventional CO2 container to which it is to be coupled, and an elastomeric seal 28 is provided for sealing thereto. A non-return valve 29 according to known art is positioned in an entry passageway 30 formed in the tie-bar 20 and at the centre of the elastomeric seal 28 as shown in Figure 2, so that coupling of the vapour offtake regulator to the CO2 container causes the right-hand (as in Figure 2) extremity of the non-return valve 29 to press upon and thus open the usual fill/dispense valve (not shown) of the CO2 container, allowing CO2 to flow through the non-return valve 29, the entry passageway -30 and into the internal chamber 24.

The opening referred to above, in the vicinity of the centre of volume of the chamber 24, is constituted by the mouth 311 of an exit conduit or vapour offtake 31 formed in the tie-bar 20 and it is found that, for a suitable working period, the level of any liquid CO2 in the chamber 24 falls short of the level of the mouth 311 of this exit conduit whatever the attitude of the vapour offtake regulator. Substantially the whole of the fluid entering the exit conduit 31 will therefore be in the form of CO2 vapour. The exit conduit 31 constrains fluid to flow, via a central bore 32, to a filter disc 33 which is advantageously made of sintered bronze which has the property of preventing the passage of any slight admixture of liquid CO2 whilst allowing CO2 vapour to pass through it.Alternatively, or in addition, a filter may be provided in the mouth 311 of the exit conduit 31 or at any point in the exit conduit 31 or the central bore 32.

CO2 vapour is then led by a feed bore 34 in the body member 22 to a pressure regulator 35, constituted by a control valve poppet 36 urged by a valve return spring 37 against a valve seat 38, a control piston 39, a control spring 40 and a regulator plunger 41. An outlet 42 from the pressure regulator 35 allows CO2 vapour at regulated pressure to be supplied to any external apparatus requiring it. The feed bore 34, valve 36,38 and outlet 42 together constitute an outlet conduit to be connected to such external apparatus.

The vapour offtake regulator is provided with a hand-squeeze lever 43 pivoted by means of a hinge pin 44 so as to bear upon the regulator plunger 41. This allows the squeezing force (illustrated in Figure 2 by the arrow 45) to be translated into a compressive force in the control spring 40 and a corresponding upward (as in Figure 2) force on the control piston 39. If this force is greater than the downward (as in Figure 2) force generated by the pressure of the CO2 vapour (in the outlet 42) acting upon the control piston 39, the control piston moves upward so as to open the control valve poppet 36 until the pressure of vapour in the outlet 42 balances the upward force on the control piston. By this means the pressure in the outlet will correspond to the squeezing force 45.

Moreover, if the manual squeezing force on the lever 43 is relaxed completely, the control valve poppet 36 acts as an ON/OFF valve and shuts off flow of CO2 to the outlet 42.

The capacity of the vapour offtake regulator (in terms of its working period or of the rate of flow of vapour that it can produce) may be increased by providing the exterior surface of the chamber with means to promote heat exchange with the environment, such as fins (not shown) protruding from the exterior surface, or a jacket (i.e. an annular enclosure) around the tubular shell 23, filled with a heat storage substance having a phase-change temperature a few degrees below ambient temperature. By this means the heat storage substance can supply thermal energy for the vaporisation of any liquid CO2 flowing into the chamber 24 during the working period of the vapour offtake regulator, and can recover that thermal energy from the surroundings in the intervals beteen a succession of working periods.

Claims

Claims

1. Apparatus for supplying a vapour substantially free of liquid from a pressurised container of a pressureliquefiable gas containing a mixture of said vapour and liquid, said apparatus comprising a chamber, means for attaching the chamber to the container, an entry passageway incorporating a non-return valve for introducing said mixture into the chamber, and an exit conduit extending from an opening in the vicinity of the centre of volume of the chamber, so that substantially only vapour will leave through the exit conduit, irrespective of the attitude of the chamber, until the level of the liquid has risen to reach the vicinity of the centre of volume of the chamber.

2. Apparatus according to claim 1 wherein the chamber is defined, at least in part, by a cylindrical wall portion and a headed passage-defining member which closes one end of the cylindrical wall portion and extends within said wall portion, the passage-defining member being formed internally with the entry passageway and the exit conduit, both of which open from the passage-defining member into the chamber, with the opening of the exit conduit located in the vicinity of the centre of volume of the chamber.

3. Apparatus according to claim 2 wherein the chamber is further defined by a headed body member which closes the other end of the cylindrical wall portion, said body member being secured to the passage-defining member and being formed internally with an outlet conduit for the vapour communicating with the exit conduit in the passage-defining member.

4. Apparatus according to claim 3 wherein the body member and the passage-defining member are screw-threadedly engaged with one another.

5. Apparatus according to claim 5, wherein the non-return valve is covered by a thrust plate which permits thrust to open a valve on a container of the pressurised fluid when the apparatus is attached to said container.

7. Apparatus according to any one of claims 4 to 6, wherein the body member includes a pressure-regulating mechanism to control the pressure of vapour emerging from the outlet conduit.

8. Apparatus according to claim 7, wherein the pressureregulating mechanism comprises a control valve poppet urged by a spring against an annular valve seat, a stem portion of said poppet passing through said annular valve seat to engage with a thrust surface of a control piston, operation of which can lift the poppet off the valve seat to permit delivery of vapour through the outlet conduit.

9. Apparatus according to claim 8, wherein the control piston is urged against the valve poppet by a further spring compressed between said control piston and a regulator plunger, movement of which varies the pressure of said further spring on the control piston, so as to vary the lift of the poppet off the valve seat and thereby to vary the delivery of vapour through the outlet conduit.

10. Apparatus according to any one of the preceding claims, wherein a filter is located in the exit conduit to prevent liquid leaving the chamber.

11. Apparatus according to any one of the preceding claims, wherein the exterior surface of the chamber is provided with means to promote heat exchange with the environment.

12. Apparatus according to claim 11, wherein the means to promote heat exchange are fins protruding from the exterior surface.

13. Apparatus according to claim 11, wherein the means to promote heat exchange is an outer jacket surrounding the chamber and containing a heat storage substance between the exterior of the chamber and jacket.

14. Apparatus for supplying a vapour free of liquid from a pressurised container, substantially as hereinbefore described and as illustrated in Figs. 1 and 2 of the accompanying drawings.