The invention relates to an injection system (10) including a longitudinal barrel (11), a distally projecting tip (13) and a tip cap assembly (30), said distally projecting tip (13) being provided with a fluid passageway (14) extending therethrough, a distal surface (15) and a lateral surface (16), said tip cap assembly (30) comprising:- an elastomeric inner cap (50) having a frustoconical protrusion (54),- a rigid outer cap (40) which is or can be securely disposed around said elastomeric inner cap (50),said tip cap assembly (30) being configured so that, when said tip cap assembly closes said fluid passageway (14), said frustoconical protrusion (54) contacts said distally projecting tip (13) only at the distal surface (15).
