Elementary compressible flow problems of granular materials have been analyzed in the past few years (Ocone, R.; Astarita, G. J. Rheol. 1993, 37, 727-742), and even only moderately complex problems present subtle difficulties, because of inelasticity of particle-particle collisions. Some analogies with classical gas dynamics exist, and those make it possible to approach basic problems using tools used there. Some results can be obtained from such an approach: standing compression and rarefaction waves, thermal relaxation tails, and the like.