Abstract: A rotary compressor or expander include a cylindrical housing chamber, a rotatable cylindrical rotor mounted eccentrically with respect to housing chamber center, a cylindrical rotor liner free to move around the rotor, and a pivoting generally circular arc vane hinged to the rotor liner. Cavity or buckets engraved to the outer surface of the rotor liner together with corresponding inlet nozzle flow provide additional momentum impulse transfer from working fluid to expander eccentric rotor. The inlet of the rotary expander is equipped with a rotating valve synchronous to the eccentric rotor, regulating the admission time and duration of the entering working fluid. The exhaust of the rotary compressor is equipped with either a check valve or a rotating valve synchronizing the fluid discharge time and duration.