Double acting two stage piston type pump

A piston type pump comprising:

• a pump housing having a piston arrangement connected to a driving shaft which, when driven, sets said piston arrangement into movement;
• said piston arrangement including a first primary stage piston, a first secondary stage piston, a second primary stage piston, and a second secondary stage piston;
• said first primary stage piston being slidably seated in a first primary stage cylinder formed in said pump housing;
• said first secondary stage piston being slidably seated in a first secondary stage cylinder formed in said first primary stage piston;
• said second primary stage piston being slidably seated in a second primary stage cylinder formed in said pump housing;
• said second secondary stage piston being slidably seated in a second secondary stage cylinder formed in said second primary stage piston;
• said driving shaft including a first eccentric and a second eccentric which are phase shifted by 180°;
• said first secondary stage piston including a first secondary stage piston rod and said second secondary stage piston including a second secondary stage piston rod;
• said first primary stage piston and said second secondary stage piston rod being configured to be mounted on and directly driven by said second eccentric;
• and,
• said first secondary stage piston rod and said second primary stage piston being mounted on, and directly driven by, said first eccentric, wherein said driving shaft includes a cap screw;
• and, said first eccentric and said second eccentric are mounted on said cap screw, wherein said driving shaft and said cap screw are separate components.

A method for mounting a piston type pump, the method comprising:

• mounting a first secondary stage piston rod and a second primary stage piston on a first eccentric;
• interference mounting a driving shaft into the first eccentric;
• inserting the first secondary stage piston rod, the second primary stage piston, the first eccentric and the driving shaft into a pump housing;
• mounting a second eccentric on the driving shaft and aligning it with the first eccentric;
• and,
• mounting the first primary stage piston and the second secondary stage piston rod on the second eccentric, wherein said driving shaft includes a stud, said first eccentric and said second eccentric being mounted on said stud, and said driving shaft and said stud are separate components or wherein said driving shaft includes a cap screw;
• and, said first eccentric and said second eccentric are mounted on said cap screw, wherein said driving shaft and said cap screw are separate components.