Needle Valve 4 : A valve, installed in the line connected to a pressure gage, whose purpose is to dampen vibration and thus allow a more accurate reading.
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}