Abstract: A safety flow limitor of modular construction for use in gas supply lines for passing a combustible natural gas from a source to a consumer comprises a cylindrical shell defining an internal passageway in which resides an axially movable valve head member having an annular surface for mating with an annular valve-seat provided along the passageway. A coil spring having its downstream portion retained in the passageway and its upstream portion abutting the valve head member serves to bias the annular surface of the valve head member away from the annular valve-seat so as to maintain the passageway open. If there is a pressure drop downstream, then the upstream pressure acts against the force of the coil spring and moves the valve head member to a downstream position where its annular surface mates with the annular valve-seat.