I have a storage tank of 40 litres with compressed air, compressed to 9 bar (absolute), which is then fed through 8mm diameter pipe to a motor. The final pressure of the air is atmospheric (1 bar). The system is run until the storage container is depleted. Is there an equation that can find the time to take until the air runs out? Also i would like to plot this as a function of time, is there an equation to do this? I am assuming that temperature is constant.