Abstract: Disclosed herein is a steam engine suitably constructed to serve as a prime mover. The device includes a furnace in which a liquid can be heated so as to change its phase, the thus formed gas directed to an engine whereupon its expansion within piston/cylinder arrangements provides useful work. The exhausted steam, still endowed with extractable energy, is passed through various regenerative pump mechanisms and the like for very efficient utilization of much of the inherent energy.