Posted By Graham Baldwin Does anyone know how to calculate the maximum capacity of a air cylinder? At present we use 9 litre cylinders pressurised to 200 bar, we are considering changing to 6 litre cylinders pressurised to 300 bar. I'm aware of the equation used to calculate the working duration but I don't have any explaination of how the figure for the maximum capacity of the cylinder is calculated. Thanks in anticipation Graham

Posted By Stuart Nagle Go to the cylinder manufacturers. Cylinders are tested (See HSAW Act 1974) as are all bits of equipment supplied for use at work. The pressure of a cylinder will be that determined by it's construction and allowing a safety margin. The calculus explained by J Joshi is fine, but only arrives at the same answer as calculating the cylinder contents in compressed litres in relationship to the bar pressure. This could be more easily done by saying: 300 bar X 6 (litres)(cylinder capacity) x 2 = 1800 !! I dont really understand why you need this information if changing sets (or cylinders on the sets), as the main area of importance surely, is the duration of the set itself. Will the new cylinder provide the longer duration you are after, if so, whats the problem. If weight is a factor (using steel cylinders) try using carbon fibre wrapped cylinders (lighter - but not a lot). Please explain the reasons why you want this information ? stuart nagle

Posted By Jay Joshi The reason for giving the calculus was that you probably cannot consider the final pressure as 1 bar--although a simple calculation of volume x pressure will give the available volume at 1 bar. As the BA will have resistance to flow etc, the BA supplier will give information on the minimum supply cylinder pressure below which the set will not work properly etc etc. Then, you will have to use that pressure value as the final pressure to calculte the volume