Abstract: A fluid transfer device for use in wellbore drilling includes at least one pressure vessel having a fluid port at a bottom thereof for entry and discharge of one of a working fluid or a power fluid and a fluid port at a top thereof for entry and discharge of the other of the power fluid or the working fluid. The pressure vessel has a barrier fluid between the power fluid and the working fluid. Valves are coupled to the power fluid port for selective introduction of the power fluid into the at least one pressure vessel. Valves are coupled to the working fluid port such that the working fluid is constrained to flow in only one direction.