BACKGROUND OF THE INVENTION The present invention relates to gas cylinders,

modifications, and improvements thereto.

Gas cylinders are well known and are widely used in a variety of different applications. The present application is directed to making such cylinders safer to store and use.

SUMMARY OF THE INVENTION

According to the present invention there is provided a cylinder for pressurised gas, the cylinder being defined by a wall and being closed at one end and having an access valve at the opposite end, the access valve comprising a valve stem which is biased closed onto a seat by a biasing member and is openable by being displaced against the biasing member;

wherein the wall of the cylinder at the opposite end continues into an inturned portion which is an integral extension of the wall, and which defines a recess

surrounding the valve stem such that the valve stem never projects outwardly beyond the recess.

In this way, the valve stem is protected by the cylinder from knocks, accidental actuation, and/or damage. The cylinder wall may be formed as a cylindrical main body closed at one end by an end cap including the access valve. However, preferably the cylinder wall is formed from first and second shells,

the first shell comprising the one end and one part of a cylindrical side wall which terminates at an open end,

and the second shell receiving the access valve, and forming the opposite end and a second part of the

cylindrical side wall which terminates at an open end;

wherein the open end of one of the shells has a folded wall portion that is folded back on itself to create a double wall thickness in the vicinity of the open end, the open end of the other shell overlapping with the folded wall portion and the two shells being welded in the region of the folded wall portion to create a triple wall thickness in this region. The triple thickness portion provides the portion of the shells that are welded with improved

structural rigidity and mitigates the effects of any stress concentrations occurring at the interface of the two shells.

The wall may define an opening to receive a valve stem, and the valve stem seats directly onto the part of the cylinder wall which surrounds the access valve. By seating the access valve directly on the cylinder wall, rather than on an intermediary component located on the cylinder, this reduces the number of components needed in the valve, making the cylinder cheaper to manufacture.

The cylinder wall may be formed from first and second deep drawn shells,

the first shell comprising the one end and one part of a cylindrical side wall which terminates at an open end,

and the second shell receiving the access valve, and forming the opposite end and the second part of the cylindrical side wall which terminates at an open end;

wherein the first and second shells are joined at their open ends to form the complete cylinder. By being formed of two separate shells that are each deep drawn and

subsequently joined together, the cylinder is cheaper to manufacture .

The biasing member may be located within the cylinder to reduce the number of working components located outside the cylinder .

The biasing member may be a compression spring, which may be cylindrical but is preferably conical.

The first and second shells may be joined at their open ends by welding, or particularly laser welding. By laser welding the two shells together, the size of the heat affected zone around the area of the weld is reduced.

Preferably, the cylinder can contain a gas at a pressure of up to 300 bar.

The cylinder may have a water capacity less than or equal to 500ml, or more preferably less than or equal to

200ml, or even more preferably less than or equal to 100ml.

The valve stem may be arranged to be open in a direction which is outward of the cylinder, but is preferably openable by being depressed into the cylinder. This makes it easier to access. Also, by opening it in an inwards direction, the pressurised gas in the cylinder will tend to close the valve when the external force to open the valve is withdrawn, thereby providing a "fail safe" closure.

BRIEF DESCRIPTION OF THE FIGURES

The invention will now be described with reference the accompanying Figures in which:

Figure 1A shows a side view of a cylinder formed of first and second shells;

Figure IB shows a section view of the cylinder taken about the section A-A from Figure 1A; and

Figure 1C shows an enlarged section view of the valve portion of the cylinder shown in Figure IB.

Figure 2A shows a side view of the first shell from the cylinder shown in Figure 1A; and

Figure 2B shows a section view of the first shell taken about the section D-D from Figure 2A.

Figure 3A shows a side view of the second shell from the cylinder shown in Figure 1A; and

Figure 3B shows a section view of the second shell taken about the section C-C from Figure 3A.

Figure 4A shows a side view of the valve assembly used in the cylinder shown in Figure 1A; and

Figure 4B shows a section view of the valve assembly taken about the section E-E from Figure 4A.

Figures 5A-5C show various views of a first embodiment biasing member used in the cylinder shown in the Figures. Figures 6A and 6B show an alternative biasing member for use in the cylinder. DETAILED DESCRIPTION

Shown in Figure 1A is a container in the form of a cylinder 10 for storing a pressurised gas. The cylinder is formed of a first shell 12 and a second shell 14. Each of the first and second shells 12; 14 has a generally

cylindrical side wall 12C;14C comprising a first

hemispherical end 12A;14A and a second open end 12B;14B. The cylindrical side wall of each shell is approximately 1mm thick .

The size, and thus the water capacity, of the cylinder 10 can be varied depending on the intended application of the cylinder. In this example, the cylinder has a water capacity of approximately 50ml.

To join the first and second shells 12; 14, the portion of the cylindrical side wall towards the open end 12B of the first shell 12 is folded back on itself to create a double wall thickness 18 in the vicinity of the open end 12B. The portion of the cylindrical wall at the open end 14B of the second shell 14 is then overlapped with the folded wall portion 18 and the two shells 12; 14 are then welded in the region of the folded wall portion 18 to create a triple wall thickness in this region. The triple thickness portion 19 provides the welded area with improved structural rigidity and mitigates the effects of any stress concentrations occurring at the interface of the two shells 12; 14. Preferably, the weld is a laser weld to reduce the size of the heat affected zone around the area of the weld. The folded portion could equally be provided on the second shell 14 with the first shell 12 having the overlapping portion.

With reference to Figure 1C, 3A-3B and 4A-4B, an access valve 16 for controlling the amount of pressurised gas inside the cylinder 10 is located within an opening 19 in the hemispherical end 14A of the second shell 14. The access valve 16 is a deep drawn component formed generally of a cylindrical valve stem 20 which has a bulbous head 22 at its first end and a radially outwardly extending annular skirt 24 at its other end which extends back towards the head 22. The radially extending skirt contains an annular seal 26 that acts as a valve seat which is engageable against the second shell 14 to plug the opening 19 in the second shell 14. The access valve 16 is biased into sealing engagement with the second shell 14 by a biasing member 28 in the form of a conical compression spring as shown in Figures 5A-5C which acts between the bulbous head 22 of the valve 16 and the wall of the shell 14. From this closed position, the valve 16 is openable by exerting an inward force on the valve stem 20 which overcomes the opposing biasing force from the biasing member 28.

Although the biasing member 28 shown in Figures 1C, 3A- 3B and 4A-4B is located outside of the first and second shells 12; 14, the biasing member 28 could alternatively be located within the space defined by the first and second shells 12; 14, as shown in Figures 6A and 6B . In this

arrangement the biasing member 28, shown as a conical compression spring, is supported at one end on the inturned portion 18 of the cylindrical wall of the first shell 12. The other end of the spring is connected to the underside of the valve stem 20 to force the seal 26 into engagement with the second shell 14.

To prevent accidental damage or actuation of the valve 16, and to minimise the overall length of the cylinder 10, the hemispherical end 14A of the second shell 14 continues into an inturned portion 30 which is an integral extension of the shell 14, and which defines a recess within which the access valve 16 is located. Particularly, the recess is narrow enough and deep enough such that the valve stem 20 is only actuatable by a correspondingly narrow actuator (not shown), and such that the valve stem never projects

outwardly beyond the recess.

It will be appreciated that the cylinder 10 can be made of any suitable material capable of withstanding the

pressures from the gas contained within the cylinder 10. Preferably the cylinder 10 should be able to support gases contained at a pressure of up to 300 bar. Possible materials for the cylinder 10 include, but are not limited to, aluminium and steel. It will also be appreciated that the access valve could be located on the first shell 12, rather than the second shell 14.

Whilst the two shells 12; 14 have been described as cylindrical, the shape of each shell 12; 14 could be modified depending on the intended overall shape of the cylinder 10.