Vapor recovery multi-stage common-rod hydraulic compressor

A multi-cylinder fluid compressor operable to compress a working fluid, said multi-cylinder fluid compressor comprising:

• a first gas compression cylinder, divided into first and second axially aligned compression chambers by a first reciprocating gas piston, each of the first and second compression chambers of the first gas compression cylinder having an inlet and an outlet;
• a second gas compression cylinder, divided into third and fourth axially aligned compression chambers by a second reciprocating gas piston, each of the third and fourth compression chambers of the second gas compression cylinder having an inlet and an outlet;
• wherein the second gas compression cylinder has a diameter less than the first gas compression cylinder;
• wherein the first gas compression cylinder and the second gas compression cylinder are axially aligned, and substantially axially adjacent;
• wherein a second gas cylinder head of the first gas compression cylinder and a first gas cylinder head of the second gas compression cylinder are axially connected;
• wherein the first gas cylinder head of the second gas compression cylinder provides an internal inlet flow passage extending between the inlet and the third compression chamber and an internal outlet flow passage extending between the third compression chamber and the outlet,
• a common piston rod extending through said first and second axially aligned compression cylinders and operably connected with the first reciprocating gas piston and the second reciprocating gas piston;
• first and second hydraulic cylinders positioned at opposite ends of the multi-cylinder fluid compressor, with the first and second compression cylinders therebetween to axially drive the common piston rod;
• wherein the first and second hydraulic cylinders are adapted to be actuated by a hydraulic fluid supply system to reciprocally drive the common piston rod and thereby the first reciprocating gas piston and the second reciprocating gas piston.