Compressor and/or expander device

A compressed gas energy storage system comprising:

• a hydraulic vessel adapted to contain a heat transfer liquid and comprising a piston disposed therein for reciprocating movement;
• a pressure vessel fluidically coupled to the hydraulic vessel and adapted to contain the heat transfer liquid and a gas in direct contact;
• and
• a heat transfer device coupled to and disposed within the pressure vessel,
• wherein the piston is moveable in a first direction to displace at least some of the heat transfer liquid from the hydraulic vessel to the pressure vessel to contact a surface of the heat transfer device and compress gas in the pressure vessel.

A method of compressing and expanding gas using a compressed gas energy storage system, the method comprising:

• providing a hydraulic vessel adapted to contain a heat transfer liquid and comprising a piston disposed therein for reciprocating movement;
• fluidically coupling a pressure vessel to the hydraulic vessel, the pressure vessel adapted to contain the heat transfer liquid and a gas in direct contact;
• coupling a heat transfer device to an interior of the pressure vessel;
• and
• moving the piston in a first direction to displace at least some of the heat transfer liquid from the hydraulic vessel to the pressure vessel to contact a surface of the heat transfer device and compress gas in the pressure vessel.