The present paper deals with the improvement to modelling of pneumatic systems. The thermal air process inside the pneumatic chambers is modelled without using the polytrophic exponent to relate the pressure-density relationship. The model takes into account the real gases behaviour and the thermal constant time for estimating heat transfer. The polytrophic exponent is used only for adjusting the data and to improve the understanding of the system. The validity of this method is demonstrated by experiments.

Keywords: pneumatics, gas compression process, compressible fluid-flow, polytrophic index, simulation