Abstract: The invention concerns a three- or four-stage gas compressor comprising two interconnecting compression units operated by hydraulic pistons; the first unit comprises a central hydraulic section flanked by two identical and symmetrical lateral sections each incorporating the first and third stages and operated by an alternating hydraulic piston; the second unit comprises a central hydraulic section of lesser diameter than that of unit one but with equal volume of oil, and two lateral sections similar to those of unit one but of lesser diameter. In the four-stage embodiment the lateral sections of unit two comprise between them the second and fourth compression stages, while in the three-stage embodiment the lateral sections of the second unit comprise only a single section each of the second compression stage. The oil chambers relative to each unit's central section interconnect--in either embodiment--by way of a compensating valve.

Abstract: A four-stage gas compressor including: a double-acting piston operable by pressurized oil and provided with first and second hollow opposed piston rods the first of which is connected to a first-stage piston and the second of which is connected to a second-stage piston; said first and second-stage pistons being arranged to slide in first and second jackets respectively and being a sliding fit upon first and second cylindrical bodies respectively; said first and second cylindrical bodies respectively being fixed to first and second opposed heads; a first axial suction and delivery duct leading to an end face of said first cylindrical body, a third stage chamber being defined between said end face and one face of the double-acting piston; and a second axial suction and delivery duct leading to an end face of said second cylindrical body, a fourth stage chamber being defined between said end face of said second cylindrical body and the other face of the double-acting piston.