Abstract: A pressure exchange apparatus includes a main section having a plurality of internal chambers and a piston disposed in each of the chambers. The apparatus also includes a pair of fluid distributor assemblies fixed to the main section and co-axial therewith. Each of the distributors include inlet and outlet ports for communicating with one of the internal chambers and sealingly separated from the other chambers. A pair of dual disk controller assemblies each of which includes a fixed disk and a moveable disk housed in a dual disk holder for directing fluid streams from one of the ports into and out of one of the chambers is also provided.