Liquid cooled plunger system

An apparatus, comprising:

• a plunger configured to reciprocate within a fluid end, the plunger comprising:
• a first end and an opposed second end;
• a plurality of bores formed therein;
• and
• a plurality of openings formed on the first end;
• in which the second end is configured to be attached to a power end assembly;
• in which the plunger is reciprocable between a first position and a second position;
• in which, when the plunger is in the first position, the first end of the plunger is situated within the fluid end by a distance, D1, defined from the first end of the plunger to an exterior surface of the fluid end which faces the power end assembly;
• in which, when the plunger is in the second position, the first end of the plunger is situated within the fluid end by a distance, D2, defined from the first end of the plunger to the exterior surface of the fluid end which faces the power end assembly;
• in which D1 is greater than D2;
• in which each of the plurality of openings aligns with a corresponding one of the plurality of bores formed in the plunger;
• in which each bore is at least partially surrounded by the fluid end when the plunger is in the first position and when the plunger is in the second position;
• and
• a plunger packing;
• in which the plunger packing surrounds each bore when the plunger is in the first position and when the plunger is in the second position.