CPV code 42511200 designates Machinery for liquefying air or other gases in the Common Procurement Vocabulary (CPV 2008), the EU classification used to describe the subject of public contracts.
42511200 is a leaf code — the most specific level of its branch — so it can be used directly as the main CPV code of a contract notice. If it does not quite fit, check the neighbouring codes under 42511000 (Heat-exchange units and machinery for liquefying air or other gases).