One embodiment of the invention provides a method to purge air or liquid from a powered injection system. In this embodiment, the method includes driving a first pumping device in a first operational mode to inject an amount of a first liquid medium through disposable tubing and a disposable valve, driving the first pumping device in a second operational mode to deform the disposable valve, and driving a second pumping device to inject an amount of a second liquid medium through the disposable tubing and the deformed valve. In one embodiment, the first pumping device comprises a first syringe, the second pumping device comprises a second syringe, and the disposable valve comprises an elastomeric valve.