A medical device (100. 100', 100", 100"') for trans-dermal infusion of a medicament, wherein the medical device is configured to be removably fixed to the skin of a patient and the medical device is provided with an internal energy source or it is configured to receive energy from an external handheld device, comprising - a housing comprising a base and a cover, the housing enclosing: - a reservoir (20, 20', 20") for holding a medicament to be infused, - a tubing (40, 40', 40") connecting the reservoir to an infusion element, wherein the infusion element is a hollow fluid transport conduit configured to be displaceable to penetrate the skin of the patient, - a reservoir push element adapted to push a volume of medicament out of the reservoir (20, 20', 20") and - a pump (50, 50', 50") comprising a piston pumping system comprising a plurality of pistons, rods, bars and pins adapted as tubing push elements for pumping the medicament from the reservoir (20, 20', 20"), wherein the device (100, 100', 100", 100'''), comprising the reservoir, the tubing, the reservoir push element and the pump, is assembled in at least one first pre-operational arrangement and is configured to be rearranged from the at least one first pre-operational arrangement into a second pre-operational arrangement that is pre-operational assembled, wherein in the at least one first pre-operational arrangement the pump (50, 50', 50") is in a mechanically distressed condition preventing functional operation of the pump (50, 50', 50"), and the reservoir (20, 20', 20") is in an unplugged condition in order to be physically disconnected from the tubing (40, 40', 40") in order to isolate the medicament within the reservoir, wherein upon being converted from the at least one first pre-operational arrangement into the second pre-operational arrangement the reservoir (20, 20', 20") becomes fluidically connected to the tubing (40, 40', 40") by a fluidic connector of the septum-piercer type and the reservoir push element is used to fill at least a part of the inner volume of the tubing and/or of the infusion element, and wherein the medical device is configured to be converted from the second pre-operational arrangement into an operational arrangement by triggering a triggering element coupled to the infusion element by the rearrangement of the device components, wherein in the operational arrangement the pump (50, 50', 50") is enabled in a mechanically stressed condition for functional operation of the pump (50, 50', 50"). - a housing comprising a base and a cover, the housing enclosing: - a reservoir (20, 20', 20") for holding a medicament to be infused, - a tubing (40, 40', 40") connecting the reservoir to an infusion element, wherein the infusion element is a hollow fluid transport conduit configured to be displaceable to penetrate the skin of the patient, - a reservoir push element adapted to push a volume of medicament out of the reservoir (20, 20', 20") and - a pump (50, 50', 50") comprising a piston pumping system comprising a plurality of pistons, rods, bars and pins adapted as tubing push elements for pumping the medicament from the reservoir (20, 20', 20"), wherein the device (100, 100', 100", 100'''), comprising the reservoir, the tubing, the reservoir push element and the pump, is assembled in at least one first pre-operational arrangement and is configured to be rearranged from the at least one first pre-operational arrangement into a second pre-operational arrangement that is pre-operational assembled,