Piston mounting and balancing system

A piston and drive shaft assembly for a pump, comprising at least two piston assemblies having:

• first and second pistons each having a head and a connecting rod, the connecting rods defining respective first and second openings;
• first and second bearings disposed in the first and second openings and having open centers;
• first and second eccentric elements disposed in the centers of the respective first and second bearings, said first and second eccentric elements each having an axial through bore and extending axially to one side substantially no further than a face of the corresponding piston connecting rod;
• and
• first and second mass members coupled to the respective first and second pistons having different masses essentially equal to a mass difference of the first and second pistons so as to essentially equalize the total mass of each piston assembly.

A pump, comprising;

• a motor having a drive shaft;
• a crankcase housing the drive shaft and having a pair of cylinders;
• at least two piston assemblies including:
• two pistons each having a head disposed in one of the cylinders and a connecting rod extending from the head to the drive shaft;
• two bearings disposed in openings in the connecting rods axially offset along the drive shaft;
• two eccentric elements disposed in the bearings and having axial through bores receiving the drive shaft;
• and
• two mass members coupled to the pistons having different masses essentially equal to a mass difference of the pistons so as to essentially equalize the total mass of each piston assembly.