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(11) | EP 0 050 947 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Improvements in high pressure gas cylinders |
| (57) A one-piece high pressure impact-extruded aluminium gas cylinder has an upstanding
neck, in which is formed an auxiliary aperture, particularly intended to receive a
check valve which is depressible from its seating for normal operational release of
gas from the cylinder. An over pressure relief mechanism is fitted either in the mouth
of the cylinder or in a second auxiliary aperture in the neck, preferably diametrically
opposite the first auxiliary aperture. Where two auxiliary apertures are provided
the fitments therein are preferably axially short to permit a fitment in the mouth
to extend down through the neck into the main body of the cylinder. |
[0001] The present invention relates to gas cylinders for storage of gas under high pressure. Gas cylinders with which the present invention is concerned are one-piece cylinders without welded seams and have a generally cylindrical body or barrel having a closed bottom end and surmounted by an upstanding neck, but possibly somewhat .tapering neck, the neck being of smaller external dimensions than the body and greater wall thickness.
[0002] In almost all instances the outside dimensions of the neck are less than 50% of the diameter of the cylindrical body. Usually the overall height of the cylinder is 2-3 times the external diameter of the cylinder body although it may be in the range of 1.5 - 5 (or even more) times the diameter of the body.
[0003] The invention is particularly applicable to improvements in gas cylinders produced by impact- extrusion from an aluminium alloy blank, although it is possible to envisage its use in. single-piece, high pressure'gas containers produced by other methods and from other materials, particularly steel.
[0004] Gas cylinders for containment of gases under high pressure, for example 30 atmospheres and above, are formed in a single piece without welded seams, and are thus different in kind from containers employed for readily-liquefiable gases such as butane. Cold-impact extrusion of aluminium is a very satisfactory method for forming the bodies of one-piece high-pressure gas cylinders. It allows the cylindrical wall to be both seamless and of a thickness commensurate both with the diameter of the cylinder and the designed service pressure of the cylinder. At the same time it permits the cylinder to be formed with a relatively flat bottom end thicker than the cylindrical side wall to provide the necessary strength.
[0005] The cold-impact extrusion method has been ; employed for the production of conventional gps cylinders with a volume of as little as 0.5 litre, but in many instances the volume of known cylinders is 50 litres or higher.
[0006] In conventional high-pressure gas cylinders means are mounted on the cylinder to provide for turning on and off the flow of gas from the cylinder, either by a wheel valve or by means of a check valve, coacting with a means for displacing it from its seat.
[0007] For safety reasons a high-pressure gas cylinder is provided with an over-pressure relief mechanism which allows the gas to blow off from the cylinder when the internal pressure rises above a predetermined value. Such a device is to avoid the risk of explosion, when for example the cylinder is exposed to excessive heat and/or has been overfilled. Such a device requires that it be exposed at all times to the full gas pressure in the cylinder and thus must always be connected to a by-pass arranged upstream of the on-off valve for the cylinder.
[0008] Many forms of valve fitment have been developed for known high pressure gas cylinders. These are secured in the mouth aperture of the cylinder and project upwardly from the cylinder mouth. All these fitments include at least a shut-off valve (which may take the form of a simple unseatable check valve (non- return valve) and an over-pressure relief mechanism. Whatever is the design of an upwardly projecting fitment, it is preferable to provide a protector for it, at least during transport. It is well known to provide'a permanently attached protector, which also acts as a carrying handle. The employment of an upwardly projecting fitment for drawing off a supply of gas 'from the cylinder has certain other disadvantages and acts as a constraint on the employment of desirable internal fitments for the cylinder.
[0009] In its widest aspects the present invention contemplates a high-pressure gas cylinder having a mouth and at least one auxiliary aperture in the thickened neck. Such auxiliary aperture or apertures will usually have an axis approximately perpendicular to the axis of the cylinder, but in some circumstances it may be at an angle no greater than about 70° to the axis of the cylinder. The diameter of an auxiliary aperture preferably does not exceed 0.5 diameter of the neck (as measured at 90° to the axis of the aperture) although in some circumstances it maybe somewhat greater, particularly where the neck wall thickness is high in relation to the wall thickness of the cylinder body. The auxiliary aperture or apertures is/are internally screw-threaded to receive a fitment therein. Very preferably the screw thread is formed directly in the metal of the thickened neck. In some special circumstances the thread may be formed in a separate bush, secured in a plain aperture by welding, although the use of welding, even when localised, is considered undesirable in the construction of high-pressure gas cylinders.
[0010] In one arrangement employing a gas cylinder according to the invention a simple unseatable check-valve is secured as a fitment in an auxiliary aperture in the cylinder neck and the axis of the aperture is essentially perpendicular to the cylinder axis. Preferably the check-valve is housed in an externally- threaded fitment, which has a sealing surface on an external shoulder for sealing against a matching surface machined on the outside of the cylinder neck. The check-valve and its housing are screwed into the cylinder neck as a single assembly. This constitutes a preferred arrangement in accordance with the invention. This arrangement has the advantage of ease of connection of the cylinder without tools for supply of gas to related equipment. This can be achieved by means of a tubular probe, carried on a yoke, adapted to embrace the neck of the bottle to draw the probe into sealed relationship with the exit aperture of the check valve and to displace the valve member from its seating.
[0011] An overpressure relief mechanism may be threaded into the mouth of the cylinder or into an additional auxiliary aperture in the cylinder neck. The relief mechanism may be constructed so that its outer end projects very little, if at all, from the outer surface of the cylinder and thus does not require external protection. Where the relief mechanism is fitted in an additional auxiliary aperture, it is preferred that such aperture is arranged in a position diametrically opposed to the auxiliary aperture in which a check valve is fitted.
[0012] The fitting of the relief mechanism in an auxiliary aperture in the cylinder neck allows other types of desirable fitments, such as a probe or dip tube to be inserted into the mouth of the cylinder. Such a position is very desirable for any fitment which will operate most efficiently when located in alignment with the axis of the cylinder.
[0013] . A cylinder made in accordance with the invention requires a different external shape and a somewhat revised production technique, as compared with a conventionally produced cylinder.which employs an on-off valve fitment secured in the mouth of the cylinder and . projecting upwardly therefrom.
[0014] In conventional gas cylinders, the neck is made as short as possible to hold down the weight of metal in relation to the rated capacity of the cylinder. The length of the neck of a conventional cylinder need not be longer than is required to secure an on-off valve fitment to it. For the cylinder of the present invention it is necessary for the neck to extend upwardly from the shoulders of the cylinder for an extent sufficient to permit one or more auxiliary apertures to be formed in it while leaving sufficient length of neck above such aperture(s) to permit some other device to be fitted into the neck and secured by internal or external thread on the neck without prejudicing the effective operation off the device(s) in the additional aperture(s). However the overall length of the neck of a gas cylinder of the present invention may be less than the length occupied by the neck and a conventional valve fitment having a laterally directed gas outlet. This provides an opportunity for fitting a cylinder of greater capacity within a given space.
[0015] The manufacture of high-pressure gas cylinders by impact extrusion of aluminium is well suited to take advantage of the novel gas cylinder/valve combination provided by the invention. The initial body, formed by impact extrusion, has a mouth of an internal diameter equal to the diameter of the internal wall of the main body of the completed cylinder, since it is necessary to withdraw the extrusion ram through the mouth. The cylindrical wall surrounding the mouth is then reduced in diameter to provide a neck and mouth of desired final dimensions. This reduction may be achieved by pressing the mouth end of the initial extruded body, after heating to an appropriate temperature, into a female die to form the shoulders and neck of the body to the desired profile. The forming operation results in a thicknening of the wall at the shoulders and neck and results in an overall decrease in height of the initial extrusion by an amount up to about half the outside diameter of the cylindrical wall of the initial body.
[0016] As an alternative to the above procedure the neck may be formed by a metal-spinning operation.
[0017] A gas cylinder of the present invention requires a longer neck than is required for a conventional gas cylinder. In producing an aluminium alloy gas cylinder with an extruded neck in accordance with the . invention from an initial impact-extruded body the overall. reduction of the length of the initial extrusion is usually about 0.25 - 0.4 of the external diameter of the body and this is accompanied by a somewhat greater thickening over the shoulders and on the outside of the neck because of the greater extent of the initial body to which post-forming is applied. The overall length of the neck (as judged from the outside of the bottle) will in nearly all instances be at least 3 cms and will be somewhat greater than the external diameter of the neck as measured immediately surrounding the bottle mouth. To form a thus elongated neck the female die has a slight internal taper, to permit easy withdrawal at the end of the 'operation. A taper of as little as 1 has been found adequate for this purpose in most instances, but in some instances it is found desirable to provide larger tapers, even as high as 10 .
[0018] In most instances it is acceptable to bore out the auxiliary aperture(s) directly through the formed neck in spite of the slight taper of its outer surface.
[0019] In some instances it will be preferred to machine the outer surface of the neck to reduce it to a true cylindrical external shape. This option may be employed where it is desired to clamp a fitment onto the neck. Where the neck is machined or otherwise formed it may be convenient to provide a lip at the upper end of the neck. Such lip can improve the manual grippability of the neck.
[0020] Although there is a generally continuous transition from the shoulders into the neck, the bottom end of the neck may be considered to be at the point where the angle between the outer surface of the bottle neck and the axis of the cylinder increases above 15°.
[0021] In many instances a fitment to be threaded.into an auxiliary aperture in the bottle neck includes a head which seats against the external surface of.the- cylinder. In such circumstances it is preferable to provide a flat surface on the exterior of the cylinder neck. Such flat surface can be achieved by machining the neck. However it is greatly preferred to produce such a surface in the course of'forming the neck and the neck is preferably somewhat thickened at the locality of such a flat surface, so that the depth of the threaded aperture can be such as to give fully secure retention of the fitment in such aperture, while allowing for maximum economy in the use of metal in the remainder of the neck.
[0022] On a cross section of the neck the flat surface preferably makes an angle in the range of 50 - 75° with the axis of the neck. At the middle of the flat surface the wall thickness is preferably at least as thick as and preferably somewhat exceeds the wall thickness at a position at 90° to the middle of the flat surface.
[0023] In another modification such flat surfaces and thickened neck portions may be provided at diametrically opposite positions. This has the two-fold advantage of allowing two auxiliary apertures to be formed in the neck, if desired, and making the neck symmetrical so as to render the neck forming operation easier to perform.
[0024] The provision of flat surfaces in the neck in the course of the forming operation renders it unnecessary to machine a flat surface on the neck and consequently avoids the thinning of the neck that would arise in such a machining operation.
[0025] While it would be possible to provide three, four or even more flat surfaces angularly spaced around the neck there is little apparent advantage from so doing and it is currently preferred to provide a pair of flat surfaces arranged diametrically opposite to each other.
[0026] With this arrangement a fitment-receiving threaded aperture can be provided perpendicular to the flat surface without requiring any external machining of the neck, even though such flat surface may be slightly inclined to the neck axis for ease of removal of the neck from the female forming die.
[0027] The provision of one or more locally thickened portions of the neck is useful also where the head of the fitments is partially received into the neck and a sealing surface for the head of the fitment is machined in the course of drilling the aperture passage through the wall of the neck. This applies both in the case where the outer surface of the neck is as formed or has been subsequently machined.
[0028] In the accompanying drawings:-
Figure 1 is a side view, partly in section of sn aluminium high pressure gas cylinder in accordance with the invention.
Figure 2 is a section on a larger scale of the neck of the gas cylinder of Figure 1.
Figure 3 is a section of an alternative arrangement of the neck.
Figure 4 is a top end view of a cylinder with a modified neck form and
Figure 5 is a top end view of a cylinder with another modified neck form.
Figure 1 shows a side view of a cold-impact extruded aluminium cylinder intended to contain 1 kg of liquefied C02 gas.
[0029] The cylinder 1 illustrated in Figures 1 and 2 has a conventional base 2 and cylindrical side walls 3. The shoulders 4 merge into a machined truly cylindrical elongated neck 5 having an overall length of about 4 cms and has a mouth 6, which is internally screw-threaded to receive an over-pressure relief device 11 (Figure 2). The device 11 comprises a housing 12, having an internally screw-threaded bore, holding a perforated plug 14 to support a burst disc 15, which will rupture when the gas pressure in the cylinder exceeds a predetermined value. The gas then blows off to atmosphere through vent passages 16.
[0030] In accordance with the invention the elongated neck 5 has an auxiliary aperture 20 formed therein. The diameter of this aperture is about 1.5 cms and it is screw-threaded to receive a check valve 21 comprising a valve seat member 22, having a sealing rib 23 at its inner end for engagement by a sealing washer 24, carried by a plunger 25. The plunger 25 is held against its seating by a light spring 26 when the cylinder is empty but it is the gas pressure which holds it in position when the cylinder is full.
[0031] The plunger has flutes or wings 27, which guide it in the internal bore 28 of the member 22. When sufficient axial force is applied to the end button 29 of the plunger, the washer 24 is unseated and gas under pressure can pass out.
[0032] The gas cylinder is intended for use with a device, in which a pressure reduction valve is clamped to the cylinder neck, the clamp engaging in a depression 30 - diametrically opposite to the check valve.. The device carries a probe member, concentric with a take-off tube.
[0033] Tightening the clamp results in the unseating of the valve by the probe and the sealing of the take-off tube to the bore 28.
[0034] Figure 3 shows an alternative form of cylinder. In this drawing like parts are indicated by the same reference numerals as in Figure 2. In this instance there are two auxiliary apertures 20, arranged at 180 to each other. In one auxiliary aperture 20 there is a check valve 32 of reduced overall length.' It comprises a body 33, threaded into the auxiliary aperture 20 and a plunger member 34. The plunger member 34 is guided in an annular bore 35 in body 33 and is held against a seal 36 by a light spring 37, which seats against a shoulder 37' at the inner end of the auxiliary aperture 20. When adequate pressure is applied to the plunger button 38, it is unseated and gas can pass out through ports 39 in the wall 40 of the member 34.
[0035] An over pressure relief device 41, constructed similarly to the device 11 in Figure 1, is secured in the second auxiliary aperture 20.
[0037] Both the pressure check valve 32 and the over pressure relief device are made axially short so as to leave clear the axial passage in the neck 5. The wall of the cylindrical neck has a thickness of the order of 1 cm and thus the two devices are miniaturised to fall within the required length. In some circumstances the wall thickness of the neck may be as little as 0.5 cm, but in general the wall thickness of the neck of an aluminium alloy cylinder requires to be at least 1 cm and indeed the miniaturisation of the fitments to fit into an aperture, of less than 1 cm in the axial direction, presents considerable practical difficulty.
[0038] In this construction the axial passage in the neck is entirely unobstructed and is thus available for a probe or dip tube 43, extending into the lower part of the cylinder and permanently secured in the mouth 6 of the cylinder.
[0039] It is one of the advantages of the present arrangement that the check valve may be arranged at an exact distance from the lower end of the cylinder. It is difficult to achieve equal precision where the check valve is located in the side of an upwardly extending fitment threaded into the mouth of the cylinder.
[0040] The location of the check valve and pressure relief device in the cylinder neck avoids the provision of a separate fitment possibly requiring a brass or plated body and thus achieves a substantial cost saving in addition to the advantages afforded by greater compactness.
[0041] In Figures 4 and 5 an over pressure relief device 11, constructed as shown in Figure 2 is fitted , into the mouth of the cylinder and an auxiliary fitment 49, which may take the same form as the check valve 32, is fitted into an auxiliary aperture 50 in the neck. The axis of the auxiliary aperture 50 is perpendicular to the plane of a flat surface 51 on the neck of the bottle which is locally thickened at this locality.
[0042] In Figure 4 the surface 51 merges into a neck of generally circular profile. In section the surface 51 makes an angle of about 65° with the axis of the cylinder, but may make a larger or smaller angle as already explained. The surface 51 is preferably inclined at a small angle of about 1° to the axis of the cylinder, although the angle of inclination may be up to 100 as already explained.
[0043] The generally D-shaped section of Figure 4 allows the neck to be formed with maximum economy of metal. However it is frequently preferable for ease of production to adopt the neck shape of Figure 5 in which two diametrically opposite flat faces 51 are provided on the neck. In both.Figure 4 and 5 the distance d of the mid-point of surface 51 from the axis of the cylinder slightly exceeds the distance d', so that axial length of the thread in aperture 50 is sufficient on the one hand and the wall thickness in a direction at right angles to surface 51 is no more than sufficient on the other hand . It will be understood that a second screw-threaded aperture may be provided diametrically opposite the aperture 50 shown in Figure
1. A one-piece gas cylinder for containment of gas under high pressure comprising
a generally cylindrical body having a closed lower end surmounted by a thickened neck
of smaller dimensions than said generally cylindrical body, said neck having an upwardly
open mouth characterised in that at least one auxiliary aperture, adapted to receive
a fitment therein, is provided in said thickened neck.
2. A one-piece gas cylinder as claimed in claim 1 further characterised in that said
thickened neck is of at least 3 cms length in the axial direction.
3., A one-piece gas cylinder as claimed in claim 1 or 2 further characterised in that
a second auxiliary aperture is located diametrically opposite said auxiliary aperture
in said neck.
4. A one-piece gas cylinder as claimed in claim 1, 2 or 3 further characterised in
that the diameter of said auxiliary aperture is less than half the external diameter
of said neck at 90° to the axis of said aperture.
5. A one-piece gas cylinder as claimed in any preceding claim further characterised
in that the wall thickness of the neck in the region of the auxiliary aperture is
at least 1 cm.
6. A one-piece gas cylinder as claimed in any preceding claim further characterised
in that the external surface of the neck is cylindrical and is provided with - an
outwardly directed lip in the region surrounding the mouth of the cylinder.
7. A one-piece gas cylinder as claimed in any of claims 1 to 5 further characterised
in that said neck has at least one locally thickened portion having a flat external
surface, said auxiliary aperture being arranged within said flat external surface
and having its axis substantially perpendicular to the plane of said flat external
surface.
8. A one-piece gas cylinder as claimed in any of claims 1 to 6 further characterised
in that said neck has a plurality of locally thickened portions, each having a flat
external surface and at least one of said flat external surfaces having an auxiliary
aperture arranged within it, said auxiliary aperture having its axis substantially
perpendicular to the plane of said flat external surface.
9. A one-piece gas cylinder as claimed in claim 8 further characterised in that said
neck has two locally thickened portions arranged substantially diametrically opposite
one another in relation to the axis of said neck.
10.. A one-piece gas cylinder as claimed in claim 9 further characterised in that an auxiliary
aperture is arranged within the flat external surfaces of both said locally thickened
portions.
11. A one-piece gas cylinder according to any preceding claim further characterised
in that each auxiliary aperture is provided with screw thread cut directly into the
metal of the thickened neck.
12. A one-piece gas cylinder for containment of gas under high pressure comprising
an impact-extruded aluminium body, having a hollow cylindrical body portion and an
integral bottom eid, and an upstanding neck formed by reworking the upper end of said
hollow cylindrical body portion and having a maximum external diameter less than 50%
of the external diameter of said body portion, said neck having a wall thickness greater
than the wall thickness of said hollow cylindrical body portion, said neck having
a central passage therethrough terminating in a mouth at a upper end thereof, an auxiliary
internally screw-threaded aperture of a diameter of less than 50% of the external
diameter of said neck being formed in the wall of said neck and communicating with
said central passage.
13. A one-piece gas cylinder for containment of gas under high pressure as claimed
in claim 12 further characterised in that the neck tapers upwardly towards its upper
end, the taper angle being less than 10°.
14. A one-piece gas cylinder as claimed in claim 12 or 13 further characterised in
that said neck has at least one or more locally thickened portions each having a flat
external surface, an auxiliary aperture being arranged within at least one flat external
surface and having its axis substantially perpendicular to the plane of said flat
external surface.
15. A one-piece gas cylinder as claimed in claim 14 further characterised in that
said neck has two locally thickened portions arranged substantially diametrically
opposite one another in relation to the axis of said neck, and both said flat external
surfaces having an auxiliary aperture arranged within it.
16. A one-piece gas cylinder for containment of gas under high pressure comprising
a generally cylindrical body having a closed lower end and merging at its upper end
into an upstanding thickened neck, said neck having a central passage therethrough
terminating in a mouth at the upper end thereof, an internally screw-threaded auxiliary
aperture being formed in the wall of said neck to communicate with said central passage,
an unseatable check valve being secured in said auxiliary aperture and a second fitment
for performing a different function from said check valve being secured in said mouth.
17. A one-piece gas cylinder as claimed in claim 16 further characterised in that
said second fitment is an over pressure gas relief mechanism.
18. A one-piece gas cylinder for containment of gas under high pressure comprising
a generally cylindrical body having a closed lower end and merging at its upper end
into an upstanding neck, said neck having a central passage therethrough terminating
in an -internally screw-threaded mouth at the upper end thereof, a first auxiliary
internally screw-threaded aperture being formed in the wall of said neck to communicate
with said central passage at a location beneath the screw-threaded mouth, an unseatable
check valve being secured in said first auxiliary aperture, a second auxiliary internally
screw-threaded aperture formed in the wall of said neck, an over pressure gas relief
mechanism being secured in said second auxiliary aperture and a fitment, performing
a different function from said check valve and said over pressure gas relief mechanism,
being secured in said screw-threaded mouth.
19. A one-piece gas cylinder as claimed in claim 18 further characterised in that
the fitment secured in said mouth extends downwardly through said neck past the location
of said check valve.
20. A one-piece gas cylinder as claimed in claim 18 or 19 further characterised in
that said first auxiliary aperture and said second auxiliary aperture in said neck
are located in diametrically opposed positions.
21. A one-piece gas cylinder as claimed in claim 18 further characterised in that
said over pressure gas relief mechanism presents a seating for a clamp screw at a
position on the axis of said check valve.
22. A one-piece gas cylinder as claimed in claim 20 further characterised in that
said first and second auxiliary apertures are formed in locally thickened portions.