This part of ISO 23551 specifies safety, constructional and performance requirements for manual gas valves intended for use with gas burners and gas-burning appliances, hereafter referred to as ‘valves’, unless otherwise specified. This International Standard applies to following types of manual gas valves: – manual gas shut-off valve; – gas burner valve; – appliance connector valve; – “delta C” valve. This part of ISO 23551 applies to valves for gas burners and gas-burning appliances of nominal connection size up to and including DN 100 that can be used and tested independently of these appliances using fuel gases, as natural gas, manufactured gas or liquefied petroleum gas (LPG) at inlet pressures up to and including 500 kPa. It is not applicable to corrosive and waste gases. This International Standard covers type testing only.