A pressure regulator comprises a primary fluid inlet for connection to a source of high pressure fluid, a fluid outlet for connection to a space to receive the high pressure fluid, a convergent-divergent nozzle having an upstream convergent section, a throat and a downstream divergent section, the primary fluid inlet being in fluid communication with the convergent section of the nozzle; and an outlet pipe having an upstream end arranged around but radially spaced from the outlet of the divergent section of the nozzle, the outlet pipe arranged to receive fluid flow from the outlet of the divergent section of the nozzle and conduct the fluid flowing from the nozzle to the fluid outlet.