Fluid transfer devices for filling a drug pump cartridge with liquid drug contents for administration purposes. Fluid transfer device includes a dual open ended barrel partitioned by a transverse partition into a drug vial port for telescopic mounting on a drug vial and an open ended piston cylinder for slidingly receiving a piston head including a drug pump cartridge port for telescopic mounting on a leading cartridge end of a drug pump cartridge. Sliding insertion of the piston head into the piston cylinder to butt against the transverse partition urges air trapped in the compression chamber into the drug vial which in turn urges its liquid drug contents into the vented drug pump cartridge.
