Cylinder

The Diving Cylinder

The invention of the high pressure compressed air cylinder allowed man to carry with him a supply of air for underwater exploration.

A charged diving cylinder contains air at a pressure of 200-300 bars. With such great pressures, safety can only be guaranteed if the cylinder is manufactured by a specialist working to stringent specifications. Only cylinders that have been manufactured for diving should be used for diving.

Diving cylinders are made from steel or aluminium alloy.

• Steel cylinders
  are usually made by a combination of drawing and spinning, and since steel is relatively strong, cylinders made from it will have a fairly thin wall of 4-5mm.
• Alluminium alloy cylinders
  are made by extrusion and forming, and since the alloy is not as strong as steel, the walls will be quite thick, possibly as much as 11mm. The result is that, although aluminium alloy is about one third of the weight of steel, steel cylinders will usually be lighter than aluminium ones of the same internal capacity.

Cylinder Capacity and Testing

In Europe, the size of the diving cylinder is classified in terms of water capacity, this being the volume of water a cylinder would hold if filled. Diving cylinders come in many sizes from 3 to 20 litres water capacity, with the most common sizes used being 10, 12 and 15 litres. The current tank Contents can easily be calculated by multiplying the Water Capacity by the current Cylinder Pressure (in bar).

C = WC * CP

All cylinders must be regularly tested by a competent test house. The relevant standard for testing cylinders is BS5430 and no other. The test covers visual inspection and hydraulic testing. With a visual inspection every two years and a hydraulic test every four.

Cylinder Valve

The cylinder valve is fitted into the neck of the cylinder and is provided with an o ring seal so that the diving regulator can be connected to it. The valve is screwed into the cylinder neck with either a taper thread seal or a parallel thread seal and o ring. It is not recommended that divers attempt to service their own cylinder valves, unless they possess specialist skills. Provided that the cylinder valve is washed in fresh water after use and is kept clean, there should be no need for it to be serviced between the intervals of cylinder test.