CA2097713A1

CA2097713A1 - Fluid container

Info

Publication number: CA2097713A1
Application number: CA 2097713
Authority: CA
Inventors: John W. Rilett (Deceased)
Original assignee: Individual
Current assignee: BA ALUMINIUM Ltd NAME CHANGED TO ALCAN ALUMINIUM UK LIMITED; BA ALUMINIUM Ltd
Priority date: 1990-12-10
Filing date: 1991-12-09
Publication date: 1992-06-11
Also published as: JPH06509629A; TW209886B; WO1992010702A1; EP0563333A1; CN1064536A; AU9034891A

Abstract

A fluid container (1) for containing a fluid under pressure, comprising a tubular member (2) closed by a closure member (3), said closure member (3) having a tubular part (34) extending generally axially within the tubular member (2) to form at least one peripheral space (G) between the closure member (3) and tubular member (2), the space being sealed from the inside of the container and having at least one vent passage (5) leading from the space to outside the container (1). This construction enables radial pressure inside the container (1) to assist in providing a strong joint. The container (1) may include a pressure-relief safety device in the form of at least one frangible wall portion (R) of said tubular part (3A), said frangible wall portion (R) being arranged to break in the event that the pressure in the container (1) exceeds a predetermined safety limit.

Description

W092/10702 PCT/GB91/02]78 ~LUID CONTAIMER
This invention relates to a fluid container in which the fluid may be contained under pressure.
Such containers are known, for example, ~or storin~ and dispensing carbon dioxide for a variety of purposes. Such fluid containers tend to be disadvantageous in certain respects and some o the~e disadvantages are discussed in PC Patent Applicaton No. WO 82/03441, to which reference is made.
Although it is believed that embodiments of the invention described in application WO 82/03441 overcome certain disadvantages assocated with the prior art, it is now believed that these designs can be significantly improved in various respects.
~hus, the present invention provides a fluid container for containing a fluid under pressure comprising a tubular member closed by a closure member, said members being joined together by the pressure of the fluid acting radially outwardly on the closure member.
According to the present invention there is further provided a fluid container for containing a fluid under pressure, comprising a tubular member closed by a closure member, said closure member having a tubular part extending generally axially within the tubular-member to form at least one peripheral space between the closure member and tubular member, the space being sealed from the inside of the container and having at least one vent passage leading from the space to outside the container.
lhe container is preferably provided with a pressure-relief safety device in the form of at least one frangible wall portion of an inner wall arranged generally axially of the container, said SUBSTITUTE SHEET

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2 ~ ~ 7 ~ 1 3 - 2 - PCT/GB91/021~8 wall por~ion being arranged to break in the event that the pre~sure in the container exceeds a preset safety limit. ~he safety device thus acts to protect the seal between the tubular and closure members against ultimate fsilure. By so doing the inven~ on may be described as 2 "pressure activated s2fet~
joint" between the two above members.
By this aspect of the present invention it is possible for the safety device to mimic more closely the tubular member generally without undesirable approximations due to scale e~fects as tends to be the case with ~nown bursting safety devices.
~he present invention may be applicable to refillable or non-refillable fluid containers.
The inner wall is preferably provided on a tubular part of the closure member such that a gap is ~ defined between the frangible wall portion and the tubular member with at least one vent or passageway leading from said gap to outside the container. Said tubular member may be cylindrical. Preferably, the diameter of said inner wall is of the same order as the diameter of said tubular member to mimic more clo~ely the behaviour of the tubular member under pressure.
~ he material of the tubular member may be the same as the material of the closure member, for example plastics or metal, or the material of the closure member may be different from that of the tubular member. ~he closure member may be permanently attached to the tubular member for example by friction welding or may be mechanically interlocked therewith.
In one embodiment of the present invention ~5 the tubular part of the closure member is generally SUBSTITUTE S~IEET

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coaxial with the tubular member and has at leas~ one localised reglon having a wall thickness which iS
thinner (about 2.5 to 3.5 mm thic~ for a plas'ics material and 1 to 2 mm thick for metal) than the remainder of the tubular part. In this way, ur.der a~.
increasing pressure in the fluid container the thin wall portion (frangible wall portion) is able to bulge into the annular gap between the tubular member and said tubular part until it breaks and allows the pressure (and fluid from the container) to vent to atmosphere.
The closure member may have a head (the closure member may have a dome top with said head) containing a valve such as a poppet or aerosol valve or said head may instead include a frangible wall which is designed to be pierced in order to expel the contents (e.g. in the manner of a SPARKLETSTM
bulb).
The closure member may be of a modular construction allowing the selection of different types of valves or frangible walls to be used therewith and utili~ing the same tooling for refillable and non-refillable containers.
The closure member may have an annular shoulder attached to said tubular part (for example by welding) with lands being formed on said tubular part to thereby restrain the closure member from being propelled out of the tubular member in the event of said shoulder breaking away from the tubular part.
The tubular member may be formed with an annular lip to retain the closure member to the tubular member or the tubular member may be swaged or crimped to the closure member. The closure member may ~5 be screwed to the tubular member.

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The closure me~ber may be retained ~o ~he tubular member by a locking or retaining ring having an inclined edge which engages a matching angled bead on the closure member. The angle of the bead ma,y be between 5 and 50 to the radial plane, preferably between 10 and 30, for instance 20 to 25 to sal~
radial plane. The retaining ring may be seated in ar.
inner groove on the tubular member some distance in from the open end thereof and the closure member may be prevented from being expelled from the tubular member by a "wedging" action provided by the locking ring.
The tubular part of the closure member is, preferably, shaped at one end to receive peripheral sealing means (usually in the form of an O-ring seal) to seal the closure member to the tubular member.
The closure member may comprise an outer shell (e.g. of plastics) carrying an inner metal lining sealed thereto. One or more local regions of the outer shell are removed to provide one or more gaps between the lining and the wall of the tubular member. In this manner, under pressure, the metal lining can expand into the gap or gaps in the outer shell until the lining bursts allowing pressure to be vented via vents leading from said gap or gaps to outside the container. Advantageously, the design obviates the need for high-strength plastics to be used for the closure member, which would otherwise be enquired, if the closure member were to be entirely of plastics.
The closure member may be provided with a valve (e.g. aerosol valve) of simplified construction. The closure member may be shaped to receive a valve member (e.g. valve poppet), spring means and a retaining plate (where the closure member SUBSTITUTE SHET

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The container may be of a modular construction and assembled from a variety of preselectable tubular members, and two-part closure members including different valve or pressure safety components.
According to the invention there is further provided a fluid container for containing a fluid under pressure, comprising a tubular member and a closure member wherein the closure member includes a displaceable valve plug having an orifice of chosen size ànd a forward portion adapted to fracture in the event that the pressure in the container exceeds a threshold limit, the valve plug being adapted to close upon fracture of the forward portion to allow - controlled discharge of the contents of the container.
In a further aspect, the invention provides a fluid container for containing a fluid under pressure, comprising a tubular member which receives a closure member, said container being provided with a pressure-relief safety device in the form of at least one frangible wall portion of an inner wall arranged generally axially of the container, said wall portion being arranged to break in the event that the pressure in the container exceeds a preset safety limit.

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con~a:~e. w l: '3e a?pare~ e rc' lOl~nr s?e~ esc~ or~
~m'~oc ments of a -'uid c~nta .~. _n.
acoo~dance wl~:- the prese-.~ ir.ve~.tion a.e ces^~ ed, b~- W2~/ o~ ex2~?~e on'~ h ~ e~.c accomp2n.yin~ simpl~ied dra~is~-s in ~.. c:~:
Pi~ure 1 shows a se^~io.na'~ o- ~he first em~odiment of the con~ainer;
~igure 2 shows 2 section2' ~iew taken on line II-TI of ~igure 1;
~igure 3 shows a se^ond em`~o_-ment o~ ~he con~æ ner ænd is æ view si~ 'a. to ~'g~~e 1;
~ .e ~ shows a ~ ird embod ~e~.~ o~ ~he contain~~ which is 2 hælf-sec~ionæ' c~-aw2y view;
~igu-e 5 illus~rates æ fou.~`^ embodi~ent o~
the co-.~æiner;
~ig~re o shows a cut-awav V~ o~ æ L if th - embodiment OL ~he present invention;
Figure 7 shows a sixth embod_ment and a metho~d of connection of a closure mem'^er to the' tub'ular p2rt c~ the container by frict-'onal welding; and ~ re 8 shows z modified container.
~igure3 1 and 2 of the drawings show æ
fluid container 1 comprising a body or tubular member 2 closed by a bottom (located at the right-hand end of Figure t) an~ by a closure member 3 (located at the left-hand end of Figure 1).
~oth the tubular member 2 and the closure member 3 are ~nerally cylindrical. The closure member 3 has a tubular part 3a extending within the tubular member 2 a substantial amount, for exam~le about one fif~h of the length of the member 2. The closure member 3 has a dome top 3b which is normally arranged upwardly in use and is provided with a head ~l~5-S~'.T~;~.
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H which carries a central'y located poppet or aerosol valve 4 arranged on the axis X-X o4 ' hG
tubular membeF 2. An annular shoulder 3c on c'osu-e member 3 is de~ined at the junction of the dome vcp 3b and tubular part 3a and, in this example, the shoulder 3c is permanently attached to the tubula-member 2 for example by friction welding the shoulde~
3c to the annular end face 2a of the tubular member 2.
As will be evident from ~igure 1 and ~i~ure 2 an annular gap G is defined between the tubular part 3a and the tubular member 2. In this instance, both the tubular member 2 and closure member 3 are of metal alloy but they either or both could be of high-strength plastics or plastics coated metal if preferred. A localised region R of the tubular par~
3a is of reduced thickness (see ~igure 2) and is designed to burst at a particular safety pressure to allow fluid to escape from the container 1 through to atmosphere by way of three equiangularly spaced radial vents 5 leading from the annular gap G to atmosphere.~he ela~tic modulus of the closure member is preferably substantially lower than that of the tubular member, so that radial outward pressure tends to force the members together.
Additionally, the tubular part ~a is provided at its end remote from the shoulder 3c with a thickened portion in the form of an annular end shoulder S to receive an 0-ring which seals against the inside of the tubular member 2. ~hus the closure member ~ provides an inner wall W coaxially arranged with the tubular member 2 and having a frangible wall portion R. In the present example the thickness of the wall portion R is 1 to 2 mm and is designed to burst at a pressure of about 2,250 p.s.i.g. (15513 .
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~ 8 -kPa), the bursting pressure of the tubular memDer 2 being about 3,000 p.s. e. (20684 kPa).
When the ~luid container 1 is ~n u~e ~he inner wall W is under pressure and as that pressure increases the frangible wall portion R ~ends to bulge outwardly to a more and more significant extent, into the annular gap G. The frangible wall portion R
should be designed to break before touching or bearing significantly against the inside of the tubular member 2 (i.e. before traversing the annular gap G). ~he annular gap G will normally be at the same pressure as the surrounding atmosphere and thus the pressure relief device provided by the inner wall W ef~ectively mimics the cylinder wall 2b of the tubular member 2. The arrangement as so far described provides a very simple safety device which operates under conditions which are more truly representative of the pressure on the cylinder wall 2b. Additionally, and advantageously, should the weld between the shoulder 3c and the edge 2a break, the closure member 3 will not be propelled out of the tubular member 2 (like a missile) because raised lands L provided inwardly on the tubular member 2 adjacent the edge 2a will engage and retain the annular shoulder S that receives the 0-ring seal (as the closure member 3 is propelled to the left in ~igure 1 along the axis g-g).
Although the aforesaid embodiment shown in ~igure 1 has an inner wall W with one frangible wall portion R a plurality of such ~rangible wall portions may be provided angularly spaced around the axis X-g and in one such embodiment three equiangularly spaced irangible walI portions are provided. Providing a plurality of frangible wall portions and additionally providing a plurality of equiangularly spaced radial SUBSTITUTE SHEET

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g vents 5 allows gas from the container to eqcape both at a controlled rate and in a multidirectional manner which is intended to minimise jet reaction forces.
The design of the annular gap G and vents 5 is such that the fluid pressure in the annular gap G
is substantially maintained above a level below whic~.
solid phase might form from the escaping fluid; for example for liquid carbon dioxide the pressure in the gap G should be above 60.4 p.s.i.g. (416 kPa) so that solid carbon dioxide (which could block the vents preventing pressure release) does not form.
~hus, the aforedescribed embodiment eliminates the need for an expensive brass valve body and burst disc assembly and the frangible wall portion R and tubular part 3a of the closure member closely mimic the cylinder wall 2b for additional safety. In effect the fluid container 1 is double-walled over part of its length with the 0-ring (circumferential sealing means) providing fIuid-tight sealing between the closure member 3 and tubular member 2, the annular gap G allowing room for the frangible wall portion R
to expand and burst under excess pressure without bearing unduly against the cylinder wall 2b.
As shown in Figure 2 the frangible wall portion R is created by providing a flat on the inner wall W but it will be appreciated that many other forms of frangible wall portions may be provided (for example a grooved or necked area or other forms of local thinning or weakening of the inner wall W could be provided). Since the single pressure relief safety device as aforedescribed can effectively raplace the three pressure relief devices described, for example, in the-aforementioned application W0 82/03441 the closure member can advantageously be made to a size such as 17 mm diameter whilst not SUBSTITUTE SHEET

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, o --precludin~ its use in containers of up to lO0 ~m diameter or more.
Additionally, it is also a signi~icant advantage for the desi~n of conta.ner as deF-c~ed in Figures l and 2 that it is basically in two parts (namely the tubular member 2 and closure member 3).
This two-part construction of the container (rather than a one-piece integrally formed container) allows for much greater versatility in design. As shown in ~igure l the dome 3b of the closure 3 carries a poppet valve 4 and the various parts thereof have been introduced into head H of the dome 3b from the inside of the dome. Thus, a remarkably simple valve construction can be provided utilising a minimum number of parts and in a very inexpensive way. The poppet valve 4 is inteerated into the head ~ so that the head H itself provides the housing for valve poppet 4a. Poppet 4a is seated in receiving cup 4b which is spring-loaded by helically coiled compression spring 4c into contact with valve seat 4d formed on the head ~. Spring 4c bears against -retaining plate 4e in a manner which should be evident from ~igure 1 and the other drawings (see e.g. ~igure 6).
~he design of the container l may be modified, for example so that the closure member 3 mechanically interlocks with the tubular member 2 rather than being welded thereto and/or the poppet valve 4 may be replaced by other valve means, for ''!
~0 example by a frangible wall portion depending upon the use of the container.
Accordingly, Figure 3 shows a second embodiment of the present invention in which the poppet valve 4 has been replaced by a frangible wall ~5 portion Z of thickness 1 mm or so which may be SUBSTITUTE SHEET

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punctured by a piercin~ pin (not shown) in order to discharge the contents of the container 1' Additionally, the closure member 3' is attached to the tubular member 2' by an engaging beaded lip 2'a (or alternatively by an engaging lip 2'b of di~feren~
form) engaging with external peripheral projection or projections on the closure member 3. Iip 2'a is inwardly bent and outwardly folded and lip 2'b inwardly ~olded. The closure member 3 may be attached to the tubular member 2 by any one of a variety of ways such as crimping or swaging. The lip closing operations may rely upon a deformation of the lip (2'a, 2'b) and, for this reason, the material of the tubular member 2' in the region of the lip is required to exhibit an elongation before cracking or fracture of about 7% and preferably of 10% or more, in order to facilitate the lip closing operation. In this embodiment, the radial width of the annular gap G is 2.25 mm and the length of the tubular part of the closure member 3' is 30 mm.
~igure 4 shows a third embodiment of the present invention in which the closure member 3" is of high impact plastics and the tubular member 2" is of a metal alloy. In this embodiment, the closure member 3" is inserted into the open end of the tubular member 2" and the tubular member is introduced into a die to press the tubular member 2"
firmly onto the closure member 3". ~our circumferentially spaced axially extending venting grooves V are provided leading from the annular gap G". As shown a thickened band ~ is provided on the outside of inner wall portion W of the closure member 3" and this engages in an inner rece~sed portion D of - the interior of wall 2"b of tubular cylindrical member 2".

SUBSTITUTE SHEET

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W0~2/1~702 PCT/CB91~02178 ~V~J J i'~ _ 12 -~igure 5 shows a fourth embodiment of the presen~ invention in which a closure member 203 i~
screwed onto a tubular member 202 and axial venting grooves V are provided spaced around the axi~ of a container 201 leading from the annular gap G as shown. A bursting dome 204 is provided (advantageously this is moulded into the closure member 203) instead of poppet valve 4 (as shown in ~igure 1) and a rear restricter or plug 205 is inserted in position as shown from inside the dome 204. This provides a cheaper alternative to a poppet valve and different flow rates may be provided for by selecting restrictors with differently sized venting holes.
Figure 6 shows a fifth preferred form of the present invention encompassing inventive features from the various embodiments described. As shown, the closure member 403 consists basically of two parts, namely an outer plastics tubular shell 404 and an inner metal lining 405 which may simply be an inexpensive pressing. The closure member 403 has been introduced into an alloy tubular member 402 and retained in place by a locking ring r. The closure member 403 is inserted into the tubular member 402 25~ axially beyond the position shown. Then the locking ring r, which is preferably a split metal ring, is inserted into the open end of the tubular member 402 and when it reaches the inner groove in the tubular member 402 it expands outwardly to seat inside the groove. The closure member 403 is thu~ allowed to move axially outwardly from the tubular member 402 until an angled bead thereon Yeats against the inclined edge of the locking ring r. Thus, the locking ring r acts as a wedge preventing further axial outward movement of the closure member 40~.

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The angle of the bead matches the angle of the inclined edge of the locking ring r an~ this angle is preferably 25 to the vertical (radial ~lane) but m2y be between 5~ and 50. The lockin~ ring r is arranged to locate some distance from the oper. end o4 the tubular member 402 and this length of the cylindrical wall of the tubular member 402 provides an additional load bearine member to resist expansion of th plastics in order to share the load. ~he modulus of elasticity of the closure member 403 is preferably about 1/7 of the modulus of elasticity of the tubular member 402. In this embodiment, the closure member 403 is provided with a poppet valve 406 and there is no continuous annular gap G formed all the way around the inner wall W provided by the closure member 403. Instead a gap ao7 is provided locally by a cut-away area of the plastics of the closure member shell 404 in such a way that under high pressure the area of the metal lining 405 underlying the gap 407 is allowed to expand into the gap 407 until it bursts allowing pressure to vent to atmosphere via the four equiangularly spaced grooves V leading from the gap 407 to atmosphere.
Advantageously, in this arrangement 9 ince the plastics shell 404 of the closure member is shielded from direct fluid pressure by the lining 405 said plastics material can be produced to a lower grade cheaper specification (i.e. the plastics need not be high strength plastics).
~igure 7 shows a si~th embodiment of a fluid container 501 comprising a body or tubular member 502 made of metal and closed at a ~irst end by a bottom and at a second end by a closure member 503 made o~ plastics. ~he tubular member 502 is, on the inner side of the second end, roughened, for SUBSTITUTE SHEET

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, W092/10702 2 ~ ~ 7 7 1 3 . PCTtGB91/02178 e~a~?' e ~ C~t WaV OL a vlurali'J- cf o~.oo~res 502'.
Ly?~call~r the grooves 502' ar~ o.~ ~ ree? 1.2 ~
wide and ~i~h a vi~ch o 1 O ~ mre c:osure me~be~
503 has ~ ~ubula- par~ 503a a subst2n- _1 portion of wr.ich is loca'e_ inside the tubul_. me~be. 502. mhr ~ubula- ~a-~ 5G~P has ar. ir...r-- eA.c s '~ated ins ce the tubular me~ber 5~2 wh.ioh is ~. ovider '~' th, an.
annular end shoulder S provided wi~h a groove which receives an 0-rin~ Lor sealing against ~he inside of the tubular me~ber 502. The outer end of the tubul2r part 503a is situated outside the tubula- member 502 wi~h e.g. 0.6 mm inter erence an~ has a domed to~
503b proviàed wi~h a heA~d ~ which. c~ Ar ies a cent.a'ly located poppet o- Pe-osol vælve 50~ a~ n~-d on the axis of the tubular ~ember 502. An outer annular shoulder 50O providing a flange is for~r-A at the portion of the comed top 503b re~ote f.om the head -.i.
An annular gap G is defined between the tubular part 503a and the tubular member 502. The gap G is closed at one end by the shoulder S with the 0-ring and communicates by vents 505 with the atmosphere. Each of the`vents 505 is composed of an axial ven~ groove opening into a radial vent groove which is situated in the flange OL the shoulder 50O and o?ens into the atmosphere. The radial grooves should have a significantly smaller cross-sectional area than the axial grooves which feed them so that they act as bottle nec~s and thus cause a pressure build-up in the long axial groove so as to prevent the carbon dioxide from becoming solid as explained above. In a typical example the axial grooves may be about 1.5 mm deep and 2 mm wide:, while the radial grooves will be SVB~T~TU~E SHE~T
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abou~ 0.3 mm to 0.5 mm de~D ~n~307~ m~ ~o 0.5 ~.
wide. Natur21~y the cros~-sectional area will depe~d on the numoer o~ grooves provided in any particular embodime.~' and or. the ~as s'ored in t'^.e con~aine~ A
localised r~ on ~ of the tu~ula- par' 503a is of reduced thic~ess and is c~s~&ned to burs' a~ a Dar ~icu12~ sa~ety pressure ~s described earlier. ~.e tubular member 502 and the closure mes'oer 50~ are at~ached together preferahl~ by ultra_onic vibration which causes the plastics material of the closure member 5~3 to be par~l~ melted or refo-med so as to flow into the grooves 502' a.~c set ~he~ein. Suitable machines are available ~or ins~ance f.^m ~orward Ultrason~ imited which is a subsid.ary of ~Se~asonics S.A. (Prance) and ~erfurth U~ Limited, which is a subsidiary of '~er~llrth Gmb'.: (Feceral Republic of Germany). ~he machine is rated at 2-3 k'~i ~nd a suitable frequency is about 20 k;iz the dwell time being approximately 1 second. The vibration t-ansmitting element of the machine is pressed in opera'tion on to the shoulder 506. An alternative is to heat the o~en end of the tubular me~ber 502, e.g.
by induction heating, flame jets, laser, or in the oven, above the melting point of the plastics and '' -then press the closure member 503 into the tubular -member 502. Another possibility is to heat the tubular member 502 to e.g. 500-C, chill the closure ' member 503 to e.g. -150C, bring the two members together ~nd allow the hot tubular mem~er 502 to shrink onto the cold closure member 503 thus causing partly melting and partly reforming of the plastics which thereby enters into the grooves.
At least one of the tubular members or closure members may alternatively be of a material, or coated with a material, such as a plastics SU~STiTUTE SHEET
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W092t10702 ~ a ~ 3 PCT/GB91/02178 _ l6 -material, which is ~oft at rcom tem~erature or when heated to enable that member to be deformed to attach the members. Instead of a screw thread, the connection may alternatively be by a means suc:- as one or more ribs or protrusions. The ribs or protrusions may be saw-teeth and may be on the ~nside of the tubular member and/or on the outside of the closure member. They are preferably arranged, by choosing the pitch or otherwise, such that there is little ratcheting effect, ie so that the ends of the teeth do not properly engage until the member is almost completely home to avoid undue wePr on the ends of the teeth.
In one example the member may be heated at lOOC for l5 minutes, preferably by immersion in boiling water, which aids the softening. Other temperatures and heating periods may be used.
The O-ring is remotely located in the closure member 503 so as to avoid the adverse effects of the nearby heating of the tubular and/or closure members.
In the above embodiments of the invention there i8 provided a gap G which may be in the form oi a single peripheral space or a plurality of peripheral spaces which communicate or communicates via suitable vents with the atmosphere and is at the inner end closed by an annular end shoulder S with the O-ring. This vented gap G then facilities the creation of a substantial pressure difference (e.g.
of 50 MPa in the case of C02) so that the greater pressure inside the container acts radially outwardly on the tubular part of the closure member which improves the sealing and causes a situation wherein the greater the pressure in the container trying to blow it apart the harder it holds itself together because this pressure improves the seal or joint between the roughened inner surface of the tubular member and the closure member. ~hi~ arrangement allows the thinned portion mentioned above to act as SUBSTITUTE SHEET

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a pressure-bursting diaphragm.
In the aforedescribed embodimer.ts none o the vents pierces the end wall of the closure member and so, advantageously, there is no necess-ty or a top shroud (as with the arrangement depicted ir.
application WO 82/03441) to prevent t~mperin~ with the pressure relief devices. Obviation of the need for a top shroud reduces the overall cost and weight of the item and tends to increase reliability. The cross-sectional area of the vents is such that when the frangible inner wall portion has burst, the pressure in the gap between the tubular part and the tubular member remains substantially above 60.4 p.s.i.g. (415 kPa) i.e. the pressure below which solid C02 can form, thus avoiding possible blocking of the vents by the presence of solid material.
With all the aforedescribed containers, advantageously, a single two-stage proof test can be applied. With a container o~ minimum burst pressure of 3000 p.s.i.g. (20684 kPa) ? proof-testing is usually done at 2000 p.s.i.g. (13790 kPa). ~hus, the container can be tested firstly with a 2000 p.s.i.g. (13790 kPa) internal pressure and with a 500 p.s.i.g. (3447 kPa) offset pressure applied to the annular gap (through the vents) between the inner wall and the container wall. ~herefore, the inner wall is tested to a pressure difference of 1500 p.s.i.g. (10342 kPa). Then the o~fset pressure is increased to 2000 p.s.i.g. (13790 kPa) and this tests ~0 the container wall. Thus, the container can be thoroughly proof-tested.
With the above embodiments, excess pressure of the container's contents is relieved by ~racturing o~ the frangible portions, which allows the contents to be relieved relatively gently through the passages - SUBSTITUTE SHEE~

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; , W092/10702 PCT/GB91/02~78 ~ 18 -and vent ori~ices. In a preferred embod~ment, two vent orifices are included, mounted diametrically opposite one another to cancel any undesired iet reaction. In some embodiments the vents are de~igned to empty the contents of a cylinder relatively slowly, ~or example ~00 gram of contents at about 10-20 grams per second. ~owever, this rate of release may not be quick enough in severe circumstances such as the cylinder being caught in a fire, in which case the pressure ma~ rise dan~erously and possibly caùse a catastrophic explosion o4 the container.
Figure 8 shows a modi~ied apparatus which attempts to solve this problem. The cylinder head includes a small bore housing a valve poppet 604 and valve spring 605, and a larger bore in which is secured a valve plug 606, retained by two snap ridges 607. The valve plug includes slots in both the axial and radial directions to enable rapid refilling and venting. The (lefthand) end of the larger bore nearest the top of the cylinder has a sharp corner 608 which aligns obliquely with the sharp corner 609 of an undercut 610 provided at the lower end of the cylinder's coupling thread 611. The sharp corners induce a stress concentration when the cylinder is under pressure, which cau~es an incipient fracture path between them. Any other means of inducing a stress concentration leading to an incipient fracture path may alternatively be used.
In use, in an extreme ~ituation, if the irangible part of parts of a cylinder have ruptured but are unable to relieve the eas pressure quickly enough then the neck will fracture along the path between corners 608 and 609. This causes the valve plug 606 to experience a large force (typically 2500 .

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N) leftwards in the figure, movin~ it to abut agains-~
the domed inner wall 612. In this position, the radial slots 613 through which the cy'inder is refilled and vented are blockeà off. Thus, the container contents can only discharge through the small axial discharge orifice 614, the size of whi Cn is chosen for a selected rate of discharee.
Typically, it is from 0.6 to 1.5 mm diameter, allowing discharge rates of 30 to 180 grams per second for example.
The top part of the cylinder head will o course, be explosively released after fracture, but the energy of this is small, since it is only due to the smaller volume of gas contained in the voids to the left (in the Figure) of the valve plug flange.
The energy of release may be for example 20 Joules, compared to the 14,000 Joules which would be released if a cylinder exploded catastrophically. This will be followed by a safe, slow, release of gas to empty the cylinder.
~he embodiment of Figure 8 also protects against other situations. For example, when the cylinder is screwed into the socket of an appliance (such as a pressurised drinks maker or a tyre unflater) an accidential large sideways force could cause a dangerous breakage of an unprotected cylinder. With the present embodiment, the neck may fracture controllably between corners 608 and 609, leading to a small controlled explosive release of gas (of for example 20 Joules as above), followed by a substantially safe discharge.

SUBSTITUTE SHEET

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Claims

- 20 -

1. A fluid container for containing a fluid under pressure, comprising a tubular member closed by a closure member, said closure member having a tubular part extending generally axially within the tubular member to form at least one peripheral space between the closure member and tubular member, the space being sealed from the inside of the container and having at least one vent passage leading from the space to outside the container.

2. A fluid container as claimed in Claim 1 wherein the peripheral space is sealed from the inside of the container by peripheral sealing means at the end towards the bottom of the container and from the outside, except for the or each vent, by a joint at the top end of the container between the closure member and tubular member.

3. A fluid container as claimed in Claim 1 or Claim 2 including a pressure-relief safety device in the form of at least one frangible wall portion of said tubular part, said frangible wall portion being arranged to break in the event that the pressure in the container exceeds a pre-determined safety limit.

4. A fluid container as claimed in Claim 1, 2, or 3 wherein the tubular part of the closure member is generally coaxial with the tubular member and has at least one localised region having a wall thickness which is thinner than the remainder of the tubular part such that under increasing pressure in the fluid container the thin wall portion is able to bulge into the peripheral space until it breaks and allows pressure to vent to atmosphere.

5. A fluid container as claimed in any one of Claims 1 to 4, wherein the peripheral space and vent or vents are designed such that the fluid pressure in the gap is substantially maintained above the level below which a chosen escaping fluid may form the solid phase.

6. A fluid container as claimed in claim 5 wherein the or each vent comprises an axial vent groove opening into a radial vent groove which is open to the atmosphere, the or each radial groove having a smaller cross-sectional area than the axial groove which feeds it, so that it acts as a bottle neck to cause the pressure in the axial groove to be maintained above the level below which the chosen escaping fluid may form the solid phase.

7. A fluid container as claimed in any preceding claim wherein the tubular member and closure member are mechanically interlocked at a joint.

8. A fluid container as claimed in Claim 7 wherein the mating surfaces of the joint between the tubular member and the closure member are provided with serrated ridges and grooves which cooperate to provide the joint.

9. A fluid container as claimed in Claim 7 wherein the mating surfaces of the tubular member and the closure member are screw-threadedly engaged to provide the joint.

10. A fluid container as claimed in any of the Claims 1 to 5 wherein the tubular member and closure member are non-mechanically bonded at a joint.

11. A fluid container as claimed in Claim 10 wherein at least one of the tubular member and closure member are deformable to provide the joint.

12. A fluid container as claimed in any one of the preceding claims, wherein the closure member includes an annular shoulder attached to the tubular part, the tubular member or tubular part having lands formed thereon to restrain the closure member from being displaced out of the tubular member.

13. A fluid container as claimed in Claim 1 wherein the closure member includes a displaceable valve plug having an orifice of chosen size and a forward portion adapted to fracture in the event that the pressure in the container exceeds a threshold limit, the valve plug being adapted to close upon fracture of the forward portion to allow controlled discharge of the contents of the container through its orifice.

14. A fluid container for containing a fluid under pressure, comprising a tubular member and a closure member wherein the closure member includes a displaceable valve plug having an orifice of chosen size and a forward portion adapted to fracture in the event that the pressure in the container exceeds a threshold limit, the valve plug being adapted to close upon fracture of the forward portion to allow controlled discharge of the contents of the container through its orifice.

15. A fluid container as claimed in Claim 13 or Claim 14 wherein the closure member has first and second axially spaced bores, the valve plug acting to close the second bore.

16. A fluid container as claimed in Claim 15, wherein the forward portion is adapted to be released in the event of a fracture, under the pressure of gas contained in the first bore only.

17. A fluid container as claimed in any of Claims 13 to 16 wherein the forward portion is adapted to fracture upon a predetermined lateral force.

18. A fluid container as claimed in any of Claims 13 to 17 wherein the closure member has a profile which induces stress concentrations on at least one internal and external surface, to create an incipient fracture path.

19. A fluid container as claimed in any preceding claim, wherein the elastic modulus of the material of the closure member is substantially lower than the elastic modulus of the material of the tubular member.

20. A fluid container for containing a fluid under pressure, comprising a tubular member which receives a closure member, said closure member being sealed to the tubular member, said container being provided with a pressure-relief safety device in the form of at least one frangible wall portion of an inner wall arranged generally axially of the container, said wall portion being arranged to break in the event that the pressure in the container exceeds a preset safety limit.