A power turbine is provided in the form of a set of plates that cooperate to form a housing, with a set of spaced apart disks mounted on a shaft within the housing. Some of the plates and disks cooperate to allow gas or steam to be injected to provide a driving force on the shaft, while others of the disks and plates cooperate to form one or more integral pumps. The pumps are used to pull cooling liquid or water into the housing, and to cool the driving disks. In this way, the steam that drives the disks is condensed while still in the housing, with a water level maintained on the driving disks. In operation, the steam directly acts on the disks toward the outer circumference of the disks, but more toward the center of the disk, the steam transfers its energy to the water, and the water transfers the energy to the disk. Since water is less compressible and able to efficiently transfer energy to the disks, the power turbine is able to operate at relatively slow speeds, has good low-speed torque, and still has excellent conversion efficiency.