A pressure exchange device is provided that utilizes a rotor assembly inside a housing to transfer the pressure of a fluid from one high pressure fluid to another low pressure fluid. The housing may comprise a pressurized fluid contained therein to provide a sealing force to reduce fluid leakage between the spinning rotors and the housing. The sealing force and wear characteristics may be controlled to reduce leakage and wear of the pressure exchange device. The rotor assembly may be driven in either direction and the high pressure ports may be switched with the low pressure ports if desired.