ISO 2503:2009 specifies requirements for single or two-stage pressure regulators without flow-metering devices for connection to gas cylinders used for

• compressed gases up to 300 bar (30 MPa),
• dissolved acetylene,
• liquefied petroleum gases (LPG),
• methylacetylene‑propadiene mixtures (MPS), and
• carbon dioxide (CO₂)_,

for use in welding, cutting and allied processes. It does not cover pressure regulators having a nominal outlet pressure p₂ > 20 bar.

ISO 2503:2009 also specifies requirements for single or two-stage pressure regulators with flow-metering devices for connection to gas cylinders used for

• compressed gases or mixtures up to 300 bar (30 MPa), and
• carbon dioxide (CO₂),

for use in welding, cutting and allied processes. Typical processes using this equipment are: tungsten inert-gas arc welding (TIG), metal-arc inert-gas welding (MIG), metal-arc active-gas welding (MAG), plasma arc welding, tubular-cored-wiretubular-cored-wire welding and plasma cutting. Annex B gives examples of flow-control systems and their flow-measuring devices.