A fluid transfer device comprising a first reservoir (1) having a predetermined sub ambient pressure and volume and a presealed opening (1a) a second reservoir (2) containing a predetermined volume of a fluid (M) and having a presealed opening (2a) and a chamber (3) having an internal space (6) and an inlet (4) to the space (6) adapted to be connected to the opening (2a) of the second reservoir (2) and an outlet (5) from the space (6) adapted to be connected to the opening (1a) of the first reservoir (1).