This part of ISO 23551 specifies safety, constructional and performance requirements for pressure regulators intended for use with gas burners and gas-burning appliances. It also describes the test procedures for checking compliance with these requirements and provides information necessary for the purchaser and user. This part of ISO 23551 applies to pressure regulators for gas burners and gas-burning appliances of nominal connection size up to and including DN 250 that can be used and tested independently of these appliances. These regulators are suitable for fuel gases, such as natural gas, manufactured gas or liquefied petroleum gas (LPG) at inlet pressures up to and including 50 kPa. This part of ISO 23551 covers type testing only. This part of ISO 23551 does not cover a) regulators connected directly to the mains pipe work or to a container that maintains a standard distribution pressure; b) regulators installed outdoors and exposed to the environment; c) regulators which use electrical auxiliary energy.