The present invention relates to cylinders for containing a gas or gas mixture under pressure.

High pressure gas cylinders have many industrial and medical applications. Gas cylinders are frequently made from steel or aluminium alloys in order to withstand internal pressures created by the gas or gases being contained, and are subsequently heavy and difficult to handle. In a medical application or hospital environment in particular this can be a disadvantage when cylinders have to be manhandled by nurses.

It is an aim of the present invention to provide a cylinder for containing a gas or gases which is relatively light and easy to handle.

According to the present invention, a gas cylinder comprises a main hollow body portion and a neck portion to which is applied an external thread for threadably receiving a collar with a co-operating internal thread, in which the collar is made from plastics material.

In a preferred embodiment the external thread is coated with an adhesive prior to receiving the collar.

The gas cylinder may be a seamless steel or seamless aluminium alloy gas cylinder.

An embodiment of the invention will now be described, by way of example, with reference to the Figure of the accompanying diagrammatic drawing which is a section through a gas cylinder according to the present invention.

As shown, an external thread 4 is precisely machined on the neck portion 6 of a seamless steel gas cylinder 2. To the thread 4 is applied a suitable adhesive after which is screwed a plastics collar 8 formed with a co-operating internal thread.

This combination is intended to replace the currently widely used heavy metallic collar which is thermo-mechanically fixed to the neck portion of a gas cylinder. When applying the above described embodiment to a 2 litre type cylinder the efficiency (weight of gas carried per unit weight of cylinder) is approximately 20% higher than that of an equivalent cylinder using the current metallic collar arrangement. This weight saving is of particular utility in an environment, for example a hospital where extra weight could be a handicap.

The collar 8 is formed with an external thread 10 for threadably receiving a plastics guard or carrying handle (not shown).

Although reference has been made to a seamless steel gas cylinder, the plastics collar could equally be applied to a welded steel cylinder or a seamless aluminium alloy cylinder.