Precision fuel metering check valve cartridge

A diesel engine unit injector, comprising:

• a unit injector part body including a cartridge valve bore;
• a cartridge valve, including
• a valve chamber having longitudinally separated intake and outflow chamber ends in fluid communication via a chamber interior, the valve chamber including an orifice extending completely through an intake end wall to place the chamber interior in fluid communication with a space adjacent the intake chamber end, the orifice having a first cross-sectional area, and the valve chamber including a main bore extending through an outflow end wall to place the chamber in fluid communication with a space adjacent to the outflow chamber end, the main bore having a second cross-sectional area which is larger than the first cross-sectional area, and a seat area provided at a transition area longitudinally between the orifice and the main bore,
• a valve ball located within the chamber interior at a downstream position from the orifice, the valve ball being configured to selectively seal against the seat area to prevent fluid flow from entering the main bore when fluid pressure at the intake chamber end is below a predetermined cracking pressure,
• a plug located at least partially within the chamber interior and including longitudinally spaced upper and lower plug ends separated by a plug body, the upper plug end being located longitudinally adjacent, and downstream from, the valve ball and the lower plug end being located proximate the outflow chamber end, and
• a coil spring located within the chamber interior and being configured to bias the valve ball in an upstream direction toward the seat area and longitudinally away from the upper plug end, in a stable closed position, until fluid pressure at the intake chamber end reaches a magnitude greater than or equal to the predetermined cracking pressure, the coil spring laterally enclosing at least a portion of the plug body within the chamber interior,
• wherein, responsive to fluid pressure at the intake chamber end reaching the predetermined cracking pressure, the valve ball moves longitudinally in the downstream direction and into contact with the upper plug end to achieve a stable open position in which fluid is permitted to flow longitudinally past the valve ball and past at least a portion of the plug body within the chamber interior, the fluid egressing the chamber interior through the outflow chamber end;
• and
• an apertured nut configured to maintain the cartridge valve within the cartridge valve bore, the apertured nut including a longitudinally extending nut bore extending entirely therethrough to place the chamber interior of the cartridge valve in fluid communication with a fuel supply within the body of the unit injector.