ISO 15996:2005 specifies requirements for residual pressure valves, with or without a non-return function, for gas cylinders and the methods of testing such valves, for type approval. ISO 15996:2005 is applicable to valves to be fitted to gas cylinders of up to 150 l water capacity, intended to contain compressed, liquefied or dissolved gases. ISO 15996:2005 does not cover valves for fire extinguishers, cryogenic equipment or liquefied petroleum gas.