This document specifies safety, construction, performance and testing requirements for pressure regulators and pneumatic gas/air ratio pressure regulators intended for use with gas burners and gas-burning appliances. This document applies to pressure regulators and pneumatic gas/air ratio pressure regulators of nominal connection size up to and including DN 250 at inlet pressures up to and including 500 kPa, for use with natural gas, manufactured gas or liquefied petroleum gas (LPG). It is not applicable to corrosive and waste gases. This document is specifically applicable to: — positive, zero and negative pressure regulators which can use auxiliary energy to change the outlet pressure setting; — pneumatic gas/air ratio pressure regulators, which function by controlling a gas outlet pressure in response to an air signal pressure, air signal differential pressure, and/or to a combustion chamber pressure signal; — gas/air ratio pressure regulators, which function by controlling an air outlet pressure in response to a gas signal pressure or a gas signal differential pressure. This document does not cover: — pressure regulators connected directly to gas distribution network or to a container that maintains a standard distribution pressure; — pressure regulators intended to be installed in the open air and exposed to the environment; — mechanically linked gas/air ratio controls; — electronic pressure regulators and gas/air ratio regulators, which are contained in ISO 23552-1. This document covers type testing only. NOTE Annexes A to H reference the relevant annexes of ISO 23550, general requirements and are applicable where required.