Fuel injector having valve stack with vented back-up plate for check seal retention

A valve stack assembly for a fuel injector comprising:

• a plurality of coaxially arranged valve stack pieces positionable within a fuel injector body and including a check guide piece, a piston guide piece, and a back-up plate positioned axially between the check guide piece and the piston guide piece;
• an outlet check movable within the valve stack between an advanced position and a retracted position, for opening and closing a plurality of spray orifices formed in the fuel injector body;
• a check seal positioned in sealing contact with the outlet check;
• the check guide piece forming a check guide that guides the outlet check between the advanced position and the retracted position, and the piston guide piece forming a drain for draining fluid displaced during movement of the outlet check within the valve stack between an advanced position and a retracted position;
• the check guide piece and the back-up plate together defining a seal cavity receiving the check seal, and the valve stack further including a back-up plate trapping the check seal within the seal cavity, such that a crevice is formed within the seal cavity between the check seal and the back-up plate;
• and
• the back-up plate having a vent formed therein that fluidly connects the crevice to the drain.

A back-up plate for trapping a check seal in a valve stack assembly of a fuel injector comprising:

• a disc-shaped plate body having an outer perimetric edge, and an inner perimetric edge, the inner perimetric edge defining a central aperture structured for receiving an outlet check in the fuel injector and defining a longitudinal center axis extending between a first plate body side and a second plate body side;
• the disc-shaped plate body further having formed therein a plurality of dowel holes and a plurality of fuel holes, and the plurality of dowel holes and the plurality of fuel holes are arranged in a trapezoidal pattern;
• the disc-shaped plate body further having a chamfer located on the first plate body side and extending radially and axially outward from the inner perimetric edge, and a vent extending between the first plate body side and the second plate body side;
• and
• the vent including a plurality of vent holes, at least a majority of which are positioned within the trapezoidal pattern, structured for venting a fluid pressure from a crevice formed between the check seal and the back-up plate in the valve stack assembly.