Abstract: A gas supply system is described comprising: a gas capsule enclosed at one end by a pierceable diaphragm; a spacer element adjacent the pierceable diaphragm, the spacer element having a channel providing access to the pierceable diaphragm; a shaft with a piercing tip; and a seal. The shaft, spacer element and seal are arranged so that when the shaft accesses the pierceable diaphragm via the channel, the shaft is caused to enter into a sealing engagement with the spacer element via the seal before the piercing tip pierces the pierceable diaphragm. In an alternative embodiment, no spacer element is provided and instead a seal is provided in a groove in a wall defining a recess at a position so that when a gas capsule is inserted into the recess, the seal enters into a sealing engagement with the gas capsule before the piercing tip of the shaft pierces the pierceable diaphragm enclosing the gas capsule.