A system including a rotary isobaric pressure exchanger (IPX) configured to exchange pressures between a first fluid and a second fluid. The rotary IPX includes a rotor and a shaft coupled the rotor. Additionally, the system includes a hydraulic drive system including a hydraulic drive device coupled to the rotor via the shaft. The hydraulic drive device is configured to receive a hydraulic fluid and to convert hydraulic energy of the hydraulic fluid into mechanical energy to rotate the rotor at a rotational speed that is based on a flow rate of the hydraulic fluid entering the hydraulic drive device.