Pressure Device

A vessel for use in a compressor, the vessel comprising:

• at least one first wall that defines an enclosed first internal area defining a fixed volume;
• at least one second wall that at least partially defines an enclosed second internal area located in the enclosed first internal area, the enclosed second internal area being configured to hold a gas;
• at least one entry port in the at least one first wall for introducing gas into the enclosed second internal area of the vessel;
• at least one exit port in the at least one first wall for releasing gas from the enclosed second internal area of the vessel;
• at least one heating element located in the enclosed second internal area;
• an insulation layer lining an inner surface of the at least one first wall;
• and
• a controller for causing the at least one heating element to heat gas held in the enclosed second internal area of the vessel, and
• wherein the or each entry port is configured to only allow gas to enter the vessel and the or each exit port is configured to only allow gas to be released from the vessel.