The Specification applies to NRVs that are used in gas supply
installations and gas fired plants to prevent the admission of any
extraneous gases into the gas supply specified under the
requirements of the Gas Act 1986 (as amended 1995), Schedule 4,
para. 18. This applies to NRVs for the use on first and second
family gases for installations of maximum operating pressure not
exceeding 7 bar. It does not apply to valves used in oxygen or
oxygen-enriched air supplies. However, they may be used for
protection of the gas supply in oxy-gas systems provided the oxygen
pressure not exceeding 2 bar (29 lb/in2).
It also applies to both general purpose NRVs for normal low
pressure duty and also special purpose NRVs when higher operating
pressure differentials are available. The requirements for these
are identical in all respects except for the flow
This Specification applies to NRVs in the size range DN15
(nominal diameter) to DN300 (½ in NB (nominal bore) to 12 in NB)
nominal pipe size.
This Specification does not apply to NRVs using external power
sources to open or close the valve. However, the general
performance requirements may be considered relevant.