Abstract: An external infusion device system for infusing a fluid into a patient, the system including a reusable infusion device housing, a gas power source and disposable reservoir. The disposable reservoir is insertable into the reusable infusion device housing to infuse the fluid into the patient. The gas power source is for generating a gas to expel the fluid from the fluid reservoir. The disposable reservoir includes a reservoir housing, a fluid reservoir, an outlet, a gas power source, an expansion chamber and a regulating valve assembly. The fluid reservoir is within the reservoir housing for containing the fluid to be infused into the patient. The outlet is in the reservoir housing and provides a path through which the fluid is expelled to be infused into the patient. The expansion chamber is disposed between the gas power source and the fluid reservoir to receive the gas from the gas power source. The expansion member expands into the fluid reservoir to expel the fluid from the fluid reservoir.