A device according for filling a flexible container (2) with a liquid from a reservoir (3) comprises a pressurizing chamber (43), a displacement piston (41), being sealingly (42) and slideably arranged in the pressurizing chamber (43), an evacuation chamber (44), and a displacement piston (41), being sealingly (42) and slideably arranged in the evacuation chamber (44). Each chamber (43, 44) with its corresponding displacement piston (41, 41) defines an inner volume (45, 45) of the chamber (43, 44). A pressurizing conduit (51) is arranged to connect the inner volume (45) of the pressurizing chamber (43) with a reservoir adapter (13) arranged to be connected to the liquid reservoir (3) an evacuation conduit (52, 52) is arranged to connect the inner volume (45) of the evacuation chamber (44) with a container adapter (14) arranged to be connected with the flexible container (2) and a transfer conduit (53) is arranged to connect the reservoir adapter (13) with the container adapter (14). A valve (54), preferably a multiway valve, is arranged to connect the container adapter (14) either with the evacuation conduit (52, 52) or the transfer conduit (53). Advantageously in such a device the movements of the two displacement pistons (41, 41) are coupled. Preferably the movements of the two displacement pistons (41, 41) are coupled in such a way that when one displacement piston (41, 41) is shifted and de-creases the inner volume (45, 45) of the corresponding chamber (43, 44), the other displacement piston (41, 41) is also shifted and increases the inner volume (45, 45) of the corresponding other chamber (44, 43), and vice versa.
