The invention relates to a loading device provided with a tamping mechanism with which two or three functional operations needed in the sealing of punctures in blood vessels can be sequentially executed in one single manual operation. In a preferred embodiment of the tamping mechanism, a cam curve (15) transforms the single manual operation of a tamping button (8) being the one end of a plunger (14) into the retraction of a pusher (5), which has been used to insert an inner seal (1) into the vessel, and, then, the advancement of a tamping tube (10), which pushes an outer seal (2) into engagement with the outer vessel wall. In the end position of the tamping button (8), a recess (23) in the plunger (14) releases a thread (3), which tamps the inner and outer seals (1, 2) together around the intermediate vessel wall, from a retainer (16), thereby completing the third operation step.