Injector for injecting fluid

An injector for injecting fluid, comprising:

• a valve assembly comprising a valve body and a valve needle, the valve body having a longitudinal axis and comprising a cavity with a valve seat, the valve needle comprising an armature retainer, being coupled in a fixed way to the valve needle and comprising an armature retainer constriction surface, the cavity being sized to receive the valve needle therein, the cavity and the valve needle being operable to prevent in a closing position of the valve needle, in which the valve needle is seated on the valve seat, an injection of fluid from the cavity to external to the injector, and to enable the injection of fluid when the valve needle is apart from the closing position;
• and
• an electromagnetic actuator assembly, which is operable to exert a force for influencing a position of the valve needle, comprising a pole piece and an armature, the pole piece being received in the cavity, being positionally fixed within the valve body and comprising a pole piece constriction surface facing towards the armature, the armature being received in the cavity, operable to be axially displaced relative to the pole piece and to take along the armature retainer when being displaced towards the pole piece, wherein
• a fluid channel through in which fluid which enters the cavity at a fluid inlet end of the valve body and flows to a fluid outlet end of the valve body where the valve seat is positioned is defined by the armature retainer constriction surface and the pole piece constriction surface, and
• a hydraulic diameter of said fluid channel is and at least twice as large when the valve needle is in the closing position compared to the hydraulic diameter when the valve needle is at a maximum displacement away from the closing position,
• wherein the fluid channel is configured such that all of the fluid which enters the cavity at the fluid inlet end and flows to the fluid outlet end passes between the armature retainer constriction surface and the pole piece constriction surface.