Air Lock 3 : (1) Trapped air that prevents complete priming of a centrifugal pump. See also: Air Bound. (2) A dual passage used for clear access to hermetically sealed chambers
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}