Subclass 1/28: Non-positive-displacement machines or engines, e.g. steam turbines (with working-fluid flows in opposite axial directions for balancing axial thrust F01D 3/02; with other than pure rotation F01D 23/00; turbines characterised by their use in special steam systems, cycles, or processes, regulating devices therefor F01K) characterised by counter-rotating rotors subjected to same working-fluid stream without intermediate stator blades or the like traversed by the working-fluid substantially radially