Regulator 3 : A device that controls pressure, usually by changing high pressure to fairly constant low pressure; it is most commonly seen on breathing apparatus and emergency care oxygen equipment
Ralph W. Burklin & Robert G. Purington, Fire Terms: A Guide to Their Meaning and Use, National Protection Association, Boston, MA 1980 USA. (Guide: Meaning and Use, Nat Prot Association Fr Srvc - Amer) {457}