Abstract: An energy exchanger device can be used for exchanging pressure energy from one fluid to another, or may act as a hydraulic compressor or fluid driven pump. A preferred device uses a jet nozzle to rotate a cylindrical rotor block having a number of axially oriented conduits within it. As the rotor turns, one end of each of the conduits is alternately connected, through a first set of ports, to either an inlet for a high pressure fluid, or an outlet for the high pressure fluid from which the energy has been extracted. Correspondingly, the other end of each of the conduits is alternately connected to either an inlet for a low pressure fluid or an outlet for the fluid to which the energy has been transferred. A freely sliding element, such as a ball, may be placed in each of the conduits to isolate the two fluids from each other.