An oxygen concentrator system includes a portable unit and a base unit. The portable unit includes an air separation device. The base unit includes a vacuum pump. The portable unit is moveable with respect to the base unit between a connected position, in which the vacuum pump of the base unit is connected to the air separation device of the portable unit for applying vacuum pressure at the air separation device of the portable unit, and a disconnected position, in which the vacuum pump is not connected to the air separation device of the portable unit. The air separation device operates using a vacuum pressure swing adsorption (VPSA) cycle when the portable unit is in the connected position. The air separation device operates using a pressure swing adsorption (PSA) cycle when the portable unit is in the disconnected position.
