Mechanical dewateringcan be accomplished by applying vacuum on one side of the material. In suchapplications, the air flow accompanying dewatering can be substantial and energy-efficient operation requires accurate design and control of the vacuum system. The present study analyses one-dimensional, compressible flow through porous media.Three types of flow are investigated: isothermal, isentropic and adiabatic. The results are presented in terms of relations between dimensionless numbers. The main result is that the difference between assumptions of adiabatic andisothermal flow will be quite small for the majority of foreseeable process conditions.